thermal spray deposition of metals on polymer substrates€¦ · characterization of metal-to...

Thermal Spray Deposition of Metals on Polymer Substrates

by

Bobby Anand

A thesis submitted in conformity with the requirements for the degree of Master of Applied Sciences

Department of Mechanical & Industrial Engineering University of Toronto

© Copyright by Bobby Anand, 2019

ii

Thermal Spray Deposition of Metals on Polymer Substrates

Bobby Anand

Master of Applied Sciences

Department of Mechanical and Industrial Engineering University of Toronto

2019

Abstract

Aluminum and zinc were deposited using a twin-wire arc thermal spray torch onto smooth

(Ra ~0.20 µm) and rough (Ra ~ 1.60 µm) samples of polytetrafluoroethylene

(PTFE/Teflon®) and ultra-high molecular weight polyethylene (UHMW PE/ HDPE).

Aluminum coatings did not adhere to the HDPE samples, however coatings roughly 300

to 400 µm thick were obtained on PTFE. Zinc adhered well to both surfaces. Adhesion

tests and SEM imaging were performed to determine the strength and adhesion

mechanism of the coatings. Increasing surface roughness enhanced coating adhesion

strength. Additionally, deposition onto polymer substrates that were heated close to their

glass-transition/softening temperatures resulted in increased adhesion strengths. SEM

imaging suggested that mechanical interlocking increased with the metal onto a rough

surface. Heating PTFE resulted in softening, increasing Interlocking, and the PE surface,

with lower softening temperature, eroded by the impact of hot aluminum particles which

removed the surface roughness and prevented adhesion.

iii

Dedication

To My Mother and Father,

Sarita & Sunil Anand

The journey towards achieving my goals

has always been rocky, and even when

everything is working against me… I know,

without a doubt that you two will be there

to support and encourage me, as the man I am.

iv

Acknowledgments

First, I would like to express my gratitude to my supervisor, Professor Sanjeev Chandra

for offering me this amazing opportunity, and for the all his guidance throughout the

course of this project. I am sincerely grateful for the person I am today, thanks to

Professor Chandra’s insight, and approach towards research in the engineering field.

I would also like to thank my colleagues and friends, the members of the Centre for

Advanced Coating Technologies (CACT) for their constant support and encouragement

these last two years. Thank you, Dr. Larry Pershin, for teaching me everything about

thermal spraying, and showing me the organization and resourcefulness needed in

engineering. This journey would not be the same without the help and support of Chen

Feng, Michael Gibbons, Jordan Bouchard, Khalil Sidawi, Sudarshan Devaraj, and the

great Ramgopal Varma Ramaraju.

Additionally, I would like to thank Professor André McDonald for his guidance and insight

throughout this project, and N.S.E.R.C Strategic Network: Green Surface Engineering for

Advanced Manufacturing (Green S.E.A.M). Thank you, for the opportunity to learn more

about environmental solutions and practices conducted by my fellow Canadian

researchers.

Finally, thank you to the members of the MIE Machine Shop; Ryan Mendell, Shawn

Miehe, and Jeethendra Anayat for giving me the opportunity to master machining and to

bring my own designs to life.

v

Table of Contents

Abstract .......................................................................................................................... ii

Dedication ..................................................................................................................... iii

Acknowledgments ........................................................................................................ iv

List of Tables .................................................................................................................. x

List of Figures ............................................................................................................... xi

Nomenclature/Notation ............................................................................................... xv

Chapter 1 Introduction ..................................................................................................... 1

Metallization of Polymers .......................................................................................... 1

1.1 Motivation .............................................................................................................. 1

1.1.1 Why Metal Coated Polymers? .................................................................... 1

1.1.2 Industrial Appeal and Environmental Impacts ............................................ 1

1.2 Literature Review .................................................................................................. 3

1.2.1 Surface Modifications of Carbon Fiber Reinforced Polymers ..................... 3

1.2.2 Metal Bond-Coats to Aid in Polymer Metallization ...................................... 4

1.2.3 Manufactured Fiber Reinforced Polymer Matrices ..................................... 5

1.3 Research Objectives ............................................................................................. 7

1.4 Thesis Organization .............................................................................................. 8

Chapter 2 Experimental Method ..................................................................................... 9

Polymer Metallization Methodology ......................................................................... 9

2.1 Introduction ........................................................................................................... 9

2.2 Substrates, Surface Preparation and Analysis ...................................................... 9

2.2.1 The Polymer Substrates (PTFE & HDPE) .................................................. 9

2.2.2 Surfometer Measurements and Data Collection ....................................... 11

vi

2.2.3 Sand Blasting Apparatus and Procedure .................................................. 13

2.2.4 Pre-Spraying Chemical Treatment ........................................................... 15

2.3 Thermal Spray Techniques and Coating Deposition ........................................... 15

2.3.1 What is Thermal Spraying? ...................................................................... 15

2.3.2 Thermal Spray Process: Twin-Wire Arc .................................................... 16

2.3.3 Spraying Apparatus and Procedure.......................................................... 17

2.4 Adhesion Apparatus ............................................................................................ 18

2.4.1 PosiTest™ Adhesion Pull-Test Device ..................................................... 18

2.4.2 Pull-Test Methodology .............................................................................. 19

2.5 SEM Imaging and Cold-Mount Polishing ............................................................. 20

2.5.1 Cold-Mounting and Polishing .................................................................... 20

2.5.2 Scanning Electron Microscopic (SEM) Imaging ........................................ 22

2.6 Substrate Heating Methods ................................................................................. 23

2.6.1 Wire-Arc Heating Apparatus ..................................................................... 23

2.6.2 Substrate Surface Heating Equipment ..................................................... 25

2.6.3 Thermal Data Collection Set-up ............................................................... 26

Chapter 3 Wire-Arc Deposition onto Polymers .............................................................. 27

Characterization of Metal-to-Polymer Adhesion ................................................... 27

3.1 Introduction ......................................................................................................... 27

3.2 Deposited Metal Wires ........................................................................................ 27

3.2.1 Properties of Metal Coatings .................................................................... 27

3.3 Surface Roughness ............................................................................................. 28

3.3.1 Uniform Roughness Profiles ..................................................................... 28

3.3.2 SEM-Images of Surface Topography ....................................................... 29

vii

3.4 Thermal Wire-Arc Coatings ................................................................................. 31

3.4.1 Coating Deposition and Limitations .......................................................... 31

3.4.2 SEM-Images of Coating Interface ............................................................ 34

3.5 Adhesion Pull-Test Results and Analysis ............................................................ 38

3.5.1 Polymer Sample Data ............................................................................... 38

3.5.2 Sample Delamination ............................................................................... 40

3.5.3 Results and Discussions .......................................................................... 42

Chapter 4 Coating onto Heated Substrates ................................................................... 43

Temperature Analysis of Wire-Arc Deposition onto Polymers ............................ 43

4.1 Introduction ......................................................................................................... 43

4.2 In-situ Temperature Measurements during Thermal Spraying ............................ 45

4.2.1 Thermal Spraying: Aluminum onto PTFE and PE .................................... 45

4.2.2 Thermal Spraying: Zinc onto PTFE and HDPE ........................................ 46

4.3 Polymer Substrate Topography: Furnace Heated ............................................... 47

4.3.1 Furnace Heated: Surfaces of PTFE/Teflon® ............................................ 47

4.3.2 Furnace Heated: Surfaces of HDPE ......................................................... 51

4.3.3 Furnace Heated: Results and Discussion ................................................. 55

4.4 Polymer Substrate Topography: Heat Gun ......................................................... 56

4.4.1 Heat Gun: Temperature Measurements and Air Jet Impingement ........... 56

4.4.2 Heat Gun: Surfaces of PTFE/Teflon® ...................................................... 58

4.4.3 Heat Gun: Surfaces of HDPE ................................................................... 61

4.4.4 Heat Gun: Results and Discussion ........................................................... 66

4.5 Heated Substrate Characterization ..................................................................... 67

4.5.1 Aluminum onto Heated PTFE and HDPE ................................................. 68

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4.5.2 Zinc onto Heated PTFE and HDPE .......................................................... 70

4.5.3 SEM-Imaging of Coating-Substrate Interface ........................................... 72

4.5.4 Adhesion Results and Discussion ............................................................ 76

Conclusions ............................................................................................................. 80

5.1 Summary and Final Remarks .............................................................................. 80

5.2 Future Work ........................................................................................................ 83

References ................................................................................................................... 84

Appendix A ................................................................................................................... 89

SEM Imaging: Porosity of Aluminum and Zinc Coatings ........................................... 89

Appendix B ................................................................................................................... 91

Temperature Measurements: Room Temperature Substrates .................................. 91

Zinc onto PTFE ................................................................................................... 91

Zinc onto HDPE .................................................................................................. 92

Aluminum onto PTFE .......................................................................................... 93

Temperature Measurements: Heated Substrates ...................................................... 94

Zinc onto Heated PTFE ....................................................................................... 94

Zinc onto Heated HDPE ...................................................................................... 95

Aluminum onto Heated PTFE .............................................................................. 96

Temperature Measurements: Heat Gun .................................................................... 97

Substrate Heating for HDPE and PTFE .............................................................. 97

Appendix C ................................................................................................................... 98

Roughness Data: Furnace Heating of PTFE & HDPE ............................................... 99

Roughness Data: Heat Gun test of PTFE & HDPE ................................................. 101

Combined Roughness Data for Heating Tests ........................................................ 102

ix

Appendix D ................................................................................................................. 103

Adhesion Pull Tests: Room Temperature Samples ................................................. 103

Adhesion Pull Tests: Coated Heated Substrates ..................................................... 105

Appendix E ................................................................................................................. 111

Design Drawings for Heating Unit ............................................................................ 111

x

List of Tables

Table 2.1: Mechanical, Thermal, and Visual Properties of HDPE & PTFE [18, 19, 21]. 11

Table 2.2: Surfometer + Piloter Parameters for Roughness Testing [22] ...................... 13

Table 2.3: Thermal Wire-Arc Spray Parameters [27]. ................................................... 18

Table 2.4: Maximum Adhesion Strength per Dolly Size for PosiTest Adhesion Tester . 19

Table 2.5: Buehler AutoMet 250 Polishing Parameters [32] ......................................... 22

Table 3.1: Overview of Metal-To-Polymer Tests ........................................................... 27

Table 3.2: Mechanical, and Thermal Properties of Aluminum and Zinc [42, 43] ........... 28

Table 3.3: Coating Deposition Per Pass on Rough & Smooth Polymer Surfaces ......... 32

Table 3.4: Adhesion Test Results of Aluminum and Zinc Coated, PTFE and HDPE ( "0"

= delaminated) .............................................................................................................. 40

Table 4.1: Adhesion strengths of tests (1-8) for room temperature (RT) and heated

substrates (HT). Samples that could not achieve coatings are indicated with (-). All

adhesion strength values are in MPa. ........................................................................... 79

xi

List of Figures

Figure 2.1: Surfometer Set-up with PTFE Sample ........................................................ 12

Figure 2.2: Roughness Testing Schematic for Standard 2x2 Samples of PTFE/HDPE 13

Figure 2.3: Econoline Sandblast Cabinet DP 36-1 [23] ................................................. 14

Figure 2.4: Sample Holder Designed (Left) and Physical Apparatus (Right) ................ 15

Figure 2.5: Wire-Arc Thermal Spray Schematic ............................................................ 16

Figure 2.6: Thermion Auto Arc, AVD 456-HD System on top of Miller Deltaweld® 652. 17

Figure 2.7: PosiTest AT-M20 Manual Adhesion Tester next to a prepared sample, and a

diagram for the self-aligning mechanism [28, 29].......................................................... 19

Figure 2.8: (Left) Buehler AutoMet 250, (Right) Polished Sample: Al coated PTFE ..... 21

Figure 2.9: (Left) Hitachi High-Tech Tabletop Microscope TM3000, (Right) Cold-

Mounted Sample Centered in SEM ............................................................................... 23

Figure 2.10: Smooth PTFE Samples inside Heating Set-Up ......................................... 24

Figure 2.11: POWERSTAT® variable transformer (Left) attached to 3 Heat cartridges

(Right) ........................................................................................................................... 24

Figure 2.12: Despatch LAC Series 2 Forced Air Oven, (Right) Mastercraft 3-Switch Heat

Gun ............................................................................................................................... 25

Figure 3.1: Uniform Substrate Surface Roughness Averages (0 = Smooth, 20 = Rough)

...................................................................................................................................... 29

Figure 3.2: x200 magnification SEM-Image of PTFE/Teflon®, Smooth (A) and Rough

(B) ................................................................................................................................. 30

Figure 3.3: x200 magnification SEM-Image of HDPE, Smooth (A) and Rough (B) ....... 30

xii

Figure 3.4: (Left) SEM Cross-sectional View of ~260 µm thick aluminum coating onto

roughened PTFE, (Right) ImageJ processed visualization of pores (white) on the top

surface of the coating (black). ....................................................................................... 32

Figure 3.5: (Left) SEM Cross-sectional View of ~260 µm thick zinc coating onto

roughened PTFE, (Right) ImageJ processed visualization of pores (white) on the top

surface of the coating (black). ....................................................................................... 33

Figure 3.6: x250 Magnification Overview (OV1-2) SEM images of ~260 µm Thick

Coating Aluminum onto PTFE (20), Along with x1.0k Magnified Images (A-D) of

Specified Interlocking Mechanisms. .............................................................................. 35

Figure 3.7: x250 Magnification Overview (OV1-2) SEM images of ~260 µm Thick Zinc

Coatings onto PTFE (20), Along with x1.0k Magnified Images (A-D) of Specified

Interlocking Mechanisms. ............................................................................................. 37

Figure 3.8: Adhesion Strength Pull-Test Data on Tests 1-8. ......................................... 39

Figure 3.9: SEM-image of aluminum delamination on right, and on left a photo of the

delamination specimen. ................................................................................................ 41

Figure 4.1: A typical temperature profile for Electric Wire-Arc Spraying using a Guided

Arm ............................................................................................................................... 44

Figure 4.2: Temperature data of a 10 Pass Electric-Wire Arc Deposition of Aluminum

onto Roughened PTFE Substrate at Room Temperature ............................................. 45

Figure 4.3: Temperature data of a 10 Pass Electric-Wire Arc Deposition of Zinc onto

Roughened PTFE Substrate at Room Temperature ..................................................... 46

Figure 4.4: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin

PTFE, and Smooth Furnace Heated PTFE ................................................................... 48


PTFE, Sandblasted Rough PTFE, and Furnace Heated Rough PTFE ......................... 50

xiii


HDPE, and Smooth Furnace Heated HDPE ................................................................. 51


HDPE, Sandblasted Rough HDPE, and Furnace Heated Rough HDPE ....................... 53

Figure 4.8: Evaluated Ra Values of Various Polymer at virgin, sand blasted, and heated

conditions. Heating Method: Furnace. (0 – Smooth, 20 – Rough) ................................ 55

Figure 4.9: Standard Temperature Profile for All Heat Gun Tests performed on Smooth

PTFE Substrate ............................................................................................................ 57

Figure 4.10: 200x and 400x Magnification SEM Images of the Surfaces of Smooth

Virgin PTFE, and Gun Heated Smooth PTFE ............................................................... 58


Virgin PTFE, Sandblasted Rough PTFE, and Gun Heated Rough PTFE ..................... 60


Virgin HDPE, and Gun Heated Smooth HDPE ............................................................. 62


Virgin HDPE, Sandblasted Rough HDPE, and Gun Heated Rough HDPE ................... 64

Figure 4.14: Evaluated Ra values of specified polymers (0 – smooth, 20 – rough) at the

virgin, sand blasted, furnace heated, and post-heat gun states. ................................... 66

Figure 4.15: Temperature verse time graph of aluminum depositing onto a roughened

PTFE substrate heated to roughly 100 °C, via heat cartridges and a variable transformer

...................................................................................................................................... 68

Figure 4.16: Temperature verse time graph of zinc depositing onto a roughened PTFE

substrate heated to roughly 106 °C, via heat cartridges and a variable transformer ..... 70

Figure 4.17: Temperature verse time graph of zinc depositing onto a roughened HDPE

substrate heated to roughly 55 °C, via heat cartridges and a variable transformer ....... 71

xiv

Figure 4.18: x250 Magnification Overview (OV1-2) SEM images of Aluminum onto

Heated PTFE (20), Along with x1.5k Magnified Images (A,C, and D) and x800

Magnification for (B) of Specified Interlocking Mechanisms. ......................................... 73

Figure 4.19: x250 Magnification Overview (OV1-2) SEM images of Zinc onto Heated

PTFE (20), Along with x1.5k Magnified Images (A-D) of Specified Interlocking

Mechanisms. ................................................................................................................. 75

Figure 4.20: Adhesion Strength Values for Room Temperature and Heated Polymers

coated with Zinc and Aluminum, at varying surface roughness averages. .................... 77

xv

Nomenclature/Notation

This section will list the acronyms used throughout the thesis, along with their

descriptions. The acronyms will be re-established within the literature, as the report

progresses.

Acronym Description

SEM Scanning Electron Microscope

ISO International Organization for Standardization

PTFE Polytetrafluoroethylene or Teflon®

PE Polyethylene

ABS Acrylonitrile Butadiene Styrene

UHMW PE Ultra-High Molecular Weight Polyethylene

HDPE Alternative to UHMWPE, High Density Polyethylene

ASTM American Society for Testing and Materials

DAQ Data Acquisition Module

DC Direct Current

AC Actual Current

IPA Isopropyl Alcohol

NIST National Institute of Standards and Technology

RA Arithmetic Mean Roughness Average

LED Light Emitting Diode

PC Personal Computer

EWA Electric Wire-Arc Spray

PMC Polymer Matrix Composites

1

Chapter 1 Introduction

Metallization of Polymers

1.1 Motivation

1.1.1 Why Metal Coated Polymers?

The metallization of polymers is a relatively new field of study that focuses on taking

advantage of the useful properties of both metal coatings and plastic substrates. The

materials selected for a large variety of modern manufactured products are chosen for

their primary attributes, that would best fit the products intended purpose. However, the

material used may have other drawbacks. Iron and steel are used in many manufactured

products but suffer from corrosion, costing Canada billions of dollars a year in repairs and

requires preventative measures such as cathodic deposition or thermal spray coatings

[1]. Polymers are not only corrosion resistant but also resist many common chemicals [2,

3]. Additionally, polymers are light weight, thermally insulating, and electrically insulating

[2]. However, they do not have the hardness of metals or high thermal conductivity. The

possibilities of cheap, light weight, corrosive resistant, intricately design products that

possess thermal, and electrical conductivity can be achieved with a commercially

available polymer coated with a thin layer of aluminum to achieve electrically conductivity

[2, 3]. The metallization of polymers will allow industries to create novel products at

potentially lower cost than conventional methods.

1.1.2 Industrial Appeal and Environmental Impacts

There has been a rising interest in several industries in the applications of metallized

polymers, as there are many possibilities with each and every combination of polymer

and metallic coating [4]. One example is in the aerospace and aviation industries that

require components that are lighter weight for fuel efficiency, but demand that the material

be corrosion resistant, thermally insulating, and flame/smoke resistant. The automotive

industry is also looking for a lighter-weight vehicle design and replacing metal parts by

polymers [2, 4]. The medical and life sciences industries desire to experiment with using

2

metal coated polymers in applications such as creating equipment that is light weight and

easy to sterilize compared to its metal counterpart [3]. There have been investigations on

using thin metal reinforced polymers stents for releasing therapeutic drugs in patients

where polymers are used for absorbing and releasing the drugs, and the metal is a

strengthening material to compensate for the weak polymer body [5].

Consequently, along with the aerospace, aviation, automotive, and medical industries

several others such as the electrical, military, and recreational industries are

investigating the use of coated polymers in their products [2]. However, polymers are

increasingly been viewed as environmentally polluting artificial resources created as a

substitute for their natural counterparts [6]. Although this may be true, polymers were

originally created as a response to environmental degradation caused by natural resource

excavation and collection [6, 7], and efforts are being made to recycle polymers [8].

As modern society desires to prevent further environmental degradation, pressure has

increased on manufacturing companies to reduce their ecological footprint [9]. There have

been incentives to switch to non-fossil energy-based products [9]. These companies

desire to adopt the metallization of polymers to reduce overall degradation through

recycling of polymers and reducing metal use [8, 9]. The benefits of using metal coated

polymers over the materials separately has already been established in Section 1.1.1,

however, the overall environmental impact of extraction either material is an increasing

concern for society, because…

• Mining operations to collect metals creating waste rock, typically 3x more

than the collect ore [10].

• Waste rock destroys wildlife habitats and pollutes recreational areas [10].

• Oxidation of Pyrite (Iron Sulfide) associated with the extraction of several

metals, pollutes water sources and soil, by producing acidic compounds

[10].

• Trapped gases within the earth are released during excavation increasing

global emissions [10].

• Mining employees are at health risks during prolonged exposure to polluted

waste rock, and trapped gasses [10].

3

The previously stated affects caused by metal extraction can be reduced by prioritizing

the recycling of polymers and minimizing metal production. In general, polymers play a

vital role in a range of materials used in society today [11]. Reuse of plastics through

mechanical and chemical recycling are the two most widely practiced methods to

reincorporate plastics back into the manufacturing system without increasing the use of

oils and gas [8]. Mechanical recycling having low cost, and high reliability (also known as

physical recycling) paired with the low cost, and reliability of thermal spray metallization

can result in a method that will ultimately improve overall product design and reduce

environmental degradation [8]. Therefore, industries should focus on metallization of

polymers in order to advance towards a more environmentally sustainable future [11].

1.2 Literature Review

Studies have been conducted on the metallization of different polymers using various

coating techniques. These studies focus on surface preparation, polymer manufacturing,

and metal depositing techniques in order to establish optimal metallic coatings on various

polymers. Common techniques such as cold spraying is often used to create metal coated

polymers, however this section will focus on thermal spray techniques that rapidly heat

the metal particles and the polymer substrate in order to establish metallic coatings. Due

to novelty of thermal spraying onto polymers, this section of the report will be divided to

focus on the aspects of successfully coated polymers, and the properties behind strong

adhesion for metal-to-polymer adhesion. The polymers that will be examined are ones of

interest to the industries mentioned in Chapter 1.1, polymers such as treated carbon fiber

reinforced polymers, and fiber reinforced polymer matrices that incorporate different

metallic components.

1.2.1 Surface Modifications of Carbon Fiber Reinforced Polymers

Ganesan et al. [2] examined the effects of surface treatment on carbon fiber reinforced

polymers (CFRP), specifically how it would affect the coating adhesion strength and splat

morphologies after plasma spraying copper. Several CFRP samples were treated using

mechanical, chemical, and thermal surface treatments. The mechanically treated

samples were prepared in a grit-blasting machine using steel sand with average diameter

of 0.71 mm. Chemically treated samples were submerged in 2-(2-butoxyethoxy)ethanol

4

for 10 minutes, then the samples were placed in trichloro-triazine (in toluene) for 24 hours,

finally the sample was treated with a alkali water solution for 2 hours. Lastly, the thermally

treated samples were exposed to plasma spray plume at 200 mm from the substrate face,

just moments prior to coating them.

The samples had roughness average values (Ra) for the untreated, chemically,

mechanically, and thermally treated samples were 6.6, 7.8, 9.3, and 6.8 µm, respectively.

The samples were then organized into two groups; samples with 100-200 µm copper

coatings, and samples with 50-60 µm copper coatings. It should be noted that the virgin

untreated sample was unable to acquire a copper coating, whereas all other surface

treated samples achieved the required thickness with little signs of delamination. Results

gathered through adhesion testing on the previously specified sampled groups, proved

that coatings were achievable through surface treatment and that mechanically and

chemically treating the surfaces resulted in the largest adhesion strengths. However, as

you increase the coating thickness overall adhesion strength decreases and mechanically

treated samples become the superior substrate.

Ganesan et al. [2] explain that chemical treatment provides higher adhesion strengths at

lower coatings because of micro keying/anchoring created by etching the surface.

However, as the coating thickness increases thermal stresses overcome these micro-

anchors and mechanical treatment prevails as the most effective means of surface

treatment for higher adhesion. Additionally, further quantitative study is needed to

ascertain various hidden physical, chemical, and mechanical phenomena between the

polymer and sprayed metal particles.

1.2.2 Metal Bond-Coats to Aid in Polymer Metallization

Gonzales et al. [12] reviewed metallizing polymer-based substrate using thermal spraying

and describe certain processes required to better improve the capabilities of metallization

for the polymer substrates. Specifically, when reviewing electric arc-wire thermal spraying

Gonzales et al. [12] referred to various experiments that found metal bond-coats allow

for deposition of thermally resistant top coatings.

5

Although, there is limited research in the field of wire-arc metallization of polymers,

Gonzales et al. [12] examined the metallization of polymer matrix composite (PMC)

substrates conducted by Lie et al. [13]. In this study, a PMC substrate was examined for

erosion resistance applications in the aerospace industry. Graphite fiber reinforced

thermo-setting polyimide, the PMC substrate, was coated with a thin layer of pure zinc as

a bond coating for a low carbon steel (filled with Ni-Cr-B-Si powder), because of its low

melting point and good wettability for polymers. All polymer samples were first coated

with 100 µm of pure zinc, and then 50 µm of carbon steel [13]. Gonzales et al. [12] points

out localized degradation that occurs on polymer substrates due to high temperature

metal particle deposition. Studies that monitor and control the polymer substrate

temperature during deposition are of interest, but very limited, hence fabrication of an

intermediate metal coating is advantageous.

Additionally, Gonzales et al. [12] examined the study performed by Guanhong et al. [14]

where they deposited an aluminum bond coat to protect the PMC-substrate from an Al2O3

ceramic coating. In this study, Guanhong et al. [14] sprayed a 40 µm aluminum bond coat

at different stand-off distances (length from spray nozzle to substrate surface) and topped

it with the 20 µm of the ceramic. The study determined that the bond-coat protected the

polymer substrate from abrasion which resulted in significant improvement to the

hardness of the coating. The bond-coat allowed the deposition of the topcoat (Al2O3

ceramic), however, to improve overall adhesion strength cooling of the substrate should

be examined.

1.2.3 Manufactured Fiber Reinforced Polymer Matrices

Rezzoug et al. [15] conducted a similar experiment to that of Ganesan et al. [2] while

adapting the concept of interlayers described by Gonzales et al. [12]. Rezzoug et al. [15],

examined the coating adhesion and mechanical properties of metallization of CFRPs with

top surface modifications during polymer manufacturing. CFRP samples were

manufactured with different upper layers that would focus on improving adhesion. Four

layers were examined within this work; a pure epoxy overflow layer (S1), pure copper

powder filler layer (S2), mixture copper and stainless-steel powder filler layer (S3), and

an aluminum mesh layer (S4). All samples were mechanically treated via sand blasting

6

using alumina sand. The arithmetic average roughness (Ra) values for these sandblasted

samples were averaged out through 10 measurements of 2 mm line scans, which resulted

in 3.2 µm for S1, 3.9 µm for S2, 4.7 µm for S3, and 3.7 µm for S4.

Adhesion tests were performed on the zinc coated CFRP samples which resulted in

adhesion strengths of 4.2 MPa for S1, 2.7 MPa for S2, 5.1 MPa for S3, and 6.5 MPa for

S4. These adhesion results were compared to zinc coated onto 1035 steel with an

adhesion strength of 7.6 MPa. Rezzoug et al. [15] reached the conclusion that S2

(Copper-filled CFRP) has the lowest adhesion strength and S4 has the highest due to the

addition of an aluminum mesh (50% increase on S1). It was concluded from this result

that good cohesion in the upper layer of CFRP provides higher adhesion strengths for

metallic coatings. Furthermore, the introduction of metallic filler powder increased the

chances of successful coatings without damaging the polymer fibers. However, this layer

does not provide as much adherence than implementation of an aluminum mesh layer,

where the aluminum mesh increases overall adhesion by 50% and causes no changes

to the polymer’s mechanical properties. Further investigation of the impact of varying

spray parameters on coating adhesion should be conducted.

7

1.3 Research Objectives

In this study the results of an experimental examination of adhesion properties for

aluminum and zinc metal coating on polytetrafluoroethylene (PTFE/Teflon®) and ultra-

high molecular weight polyethylene (PE) polymer substrates. Aluminum was selected

because of its high electrical and thermal conductivity, corrosion resistance, sound and

shock absorption, and because of it is non-toxic, light weight, and easy to recycle [16,

17]. Zinc was selected because it has a low melting point and adheres easily to most

polymers; the objectives of this study are listed below.

❖ Develop a repeatable wire-arc thermal spraying procedure to create aluminum and

zinc coatings without delamination

❖ Create a methodology to achieve uniform surface roughness on soft polymer

substrates and determine its effect on metal-to-polymer adhesion

❖ Measure adhesion strengths of metal coatings on polymers for substrates coated

at both room, and elevated temperatures.

❖ Measure the substrate temperature during spraying and evaluate causes of

delamination

❖ Determine if the glass transition temperature/range of the polymer is a significant

factor in metal-to-polymer adhesion.

8

1.4 Thesis Organization

This thesis consists of five chapters, these chapters will be described below.

Chapter Description

1 This chapter will outline the motivation of the work by proving the benefits

of the study for material considerations, industrial interests, and

environmental rehabilitation. A literature review of the current state of

research on the topic will be provided, concluding with a list of goals for the

work.

2 The procedures and equipment used through this work will be described

and explained in this chapter.

3 This chapter will describe the properties of the metal coatings and polymer

substrates, and describe the methodology developed to obtain uniform

surface roughness on polymer surfaces. Then, thermally wire-arc coatings

of both aluminum and zinc will be examined using SEM-micrographs of the

cross-sectional interface. Finally, adhesion pull tests will be used to

determine the strength of the coatings, and the effects of mechanically

treating the surfaces.

4 Temperature measurements of the substrate were done during the

spraying process, and changes in the surface topography were studied.

Coatings were applied with the polymer’s substrates maintained either

above or below the glass transition temperature to determine its effects on

polymer adhesion. SEM-micrographs of the cross-sectional interface will

be analyzed to determine adhesion mechanisms.

5 Conclusions and summarizations of the contents of chapters 3 and 4 will

be illustrated along with recommendations for future work.

9

Chapter 2 Experimental Method

Polymer Metallization Methodology

2.1 Introduction

Several different experiments were conducted to deposit thick metallic coatings on

polymer substrates. These experiments and the procedure associated with them will be

described below, along with any data collection instruments and their use. Section 0 will

examine the mechanical and thermal properties of the polymer substrates. Then, a short

description of surface preparation and examination prior to thermal spraying will be

illustrated, which include mechanical, and chemical treatment. Next, section 0 will

describe thermal spray processes with a focus on the specific process used in this

research. Subsequently, section 2.4 will present the device and procedure used to

determine adhesion strengths of the coated polymers. Then, section 2.5 will describe the

procedure for taking SEM-images of the polymer-to-metal interfaces. Finally, section 2.6

will describe the substrate heating apparatus and data collection system used during the

final testing phase.

2.2 Substrates, Surface Preparation and Analysis

2.2.1 The Polymer Substrates (PTFE & HDPE)

The two polymers used throughout this study are ultra-high molecular weight polyethylene

(PE) and polytetrafluoroethylene (PTFE/Teflon®) purchased from McMaster-Carr. The

manufacturing process used to create the polymers is skiving, a technique that prevents

work hardening while slicing thin sheets from bulk material. Precision slotted tools are

designed to the appropriate thickness and flatness to achieve a completely uniform

surface upon slicing the bulk material [18, 19].

Polyethylene is one of the most widely used polymers in the world as It can undergo many

different manufacturing processes which create a wide selection of ethylene

homopolymers and copolymers [20]. Ultra-high molecular weight polyethylene

(UHMWPE), the polymer used in this study, is a linear polymer formed through the

10

polymerization of ethylene gas in low pressure, air and moisture deficient environments.

This polymer is especially attractive for industrial use because it is:

• chemically resistant

• an electrical insulator

• has low water absorption

• is wear and impact resistance

• and finally has low water absorption.

Comparatively, PTFE/Teflon® has high heat resistance and a non-stick nature, which is

useful in coating cooking equipment. Unlike PE, tetrafluoroethylene (TFE) can rapidly

decompose during the production of PTFE, so the polymerization process must be

performed in a carefully controlled environment with a special apparatus to prevent

overheating [19]. Although, more difficult to produce, this polymer has many attractive

properties for industrial application such as…

• chemical resistance,

• electrical insulation,

• high temperature insulation,

• impact resistance,

• wear resistance,

• weather resistance,

• and low water absorption.

The following table illustrates all the mechanical and thermal properties of both polymers

(UHMWPE & PTFE), not previous stated. This figure will be referred to, throughout the

report.

11

Table 2.1: Mechanical, Thermal, and Visual Properties of HDPE & PTFE [18, 19, 21]

Properties UHMW PE / HDPE PTFE

Construction Solid Solid

Texture Smooth Smooth

Polymer Chain -(CH2-CH2)n- -(CF2-CF2)n-

Polymer Type Thermoplastic Thermoplastic

Coefficient of Friction (rating)

0.1 – 0.2 (Very Slippery) 0.05 – 0.08 (Very Slippery)

Thickness (in) 0.125 ± 0.007 0.125 ± 0.007

Width (in) 2 ± 0.02 2 ± 0.02

Length (in) 2 ± 0.02 2 ± 0.02

Color White White

Clarity Opaque Opaque

Density (g/cm3) 0.93 – 0.95 2.1 – 2.2

Linear Thermal Expansion (x 10-5 K-1)

14.0 – 19.8 11.2 – 12.6

Glass Transition/Softening (°C)

< 80 (undefined) 115 – 125

Thermal Conductivity (W/m·K)

0.41 0.25

Specific Heat (J/kg·°C) 1900 970

Thermal diffusivity (mm2/s)

0.24 0.12

Melting Point (°C) 125-138 320 - 330

Minimum Operating Temperature (°C)

-40 -212

Specifications Met

3-A Certified, ASTM D4020, ASTM D4976, ASTM D6712, Made of

FDA Listed Material

ASTM D3294, ASTM D3308, Made of FDA

Listed Material, UL 94V0

2.2.2 Surfometer Measurements and Data Collection

The arithmetic mean roughness value (Ra) will be used to represent the surface

profile [22]. This value is calculated automatically by a model 830 skid-reference piloter

equipped to a digital surfometer created by Precision Devices, Inc (PDA-400ao, Milan,

Michigan, USA) [22]. The Ra value is determined with equation 2.2 below, which is based

on American standard ASME B46.1-1995 for surface texture. The evaluation length, L,

also known as the assessment length, is the range for which values of the surface

12

features are evaluated. The function Z(x) is the profile roughness which filters spatial

frequencies along the length x ranging from 0, the starting point specified by the evaluator,

to the evaluation length. This function calculates by default the Gaussian filter with a cut-

off length of 0.80 mm, which reduces the noise in the system resulting from the curvature

of the samples, and the flatness of the testing area.

(Eq 2.1)

Figure 2.1: Surfometer Set-up with PTFE Sample

When determining average roughness of the surface, a methodology was created

according to the specific samples used in the study. According to American standard

ASME B46.1-1995 and for the 2 by 2 inch samples (50.8x50.8 cm) at least 5 sample

lengths must be taken to give an appropriate representation of the surface [22]. It was

determined that appropriately dividing the area into 9 sections will provide a satisfactory

representation of the roughness profile for the samples in this study. These sections are

dimensioned below, and parameters used in the surfometer can be found in Table 2.2

below.

13

Figure 2.2: Roughness Testing Schematic for Standard 2x2 Samples of PTFE/HDPE

Table 2.2: Surfometer + Piloter Parameters for Roughness Testing [22]

Parameter (unit) Value

Piloter Stylus PDK

Piloter Skid Mount SMT

Piloter Speed (mm/sec) 2.54

Number of Data Readings per Sample 9

Evaluation Length, L (mm) 10.16

Cutoff Length (mm) 0.080

Total roughness recordings per L 127

Roughness Filter 2RC

Pc Threshold (µm) 0.25

2.2.3 Sand Blasting Apparatus and Procedure

In this study, comparisons will be made between the smooth/slippery polymer provided

by the manufacturer and substrates mechanically treated with an aluminum-oxide

abrasive. Mechanically treating the polymer substrates was a concern addressed by

Ganesan et al. [2] when they experimented with CFRP’s and their adhesion strengths

towards thin (50-60 µm) and thick (100-200 µm) copper coatings. Sand blasting the CFRP

14

substrate resulted in localized destruction on the surface of the polymer. Sand-blasting

pressure was therefore controlled to prevent substrate degradation and copper coatings

of the desired thicknesses were achieved. Ganesan et al. [2] concluded that mechanical

treatment of the surface provided the most adhesion when creating thick coatings. This

method was implemented into this study, however modifications to the preparation

method was considered as the substrate significantly differs from the examined CFRP.

Figure 2.3: Econoline Sandblast Cabinet DP 36-1 [23]

Tests were conducted in a Econoline Sandblast Cabinet DP 36-1 (see Figure 2.3 above)

[23] using grit #20 aluminum oxide hard blasting media purchased from McMaster-Carr

(Grand Haven, Michigan, USA). The sand-blasting method required careful consideration

to prevent any damage to the polymer surface and to maintain uniform surface profiles.

First, mechanical treatment was performed on a spare aluminum sheet, this determined

the conical area of spray consistency for the tungsten carbide blast nozzle. Once the area

of consistency was determined an apparatus that can maintain repeatable nozzle-to-

substrate distances was constructed (see Figure 2.4 below). It was concluded that with

#20 Grit aluminum oxide and a consistent air pressure of 100 psi, the average roughness

15

of the samples would prove consistent at Ra = 1.58 – 1.60 µm at a nozzle spray distance

of 4 inches from the substrate.

Figure 2.4: Sample Holder Designed (Left) and Physical Apparatus (Right)

2.2.4 Pre-Spraying Chemical Treatment

Teflon® and Polyethylene are both chemically resistant to most products that clean

surfaces and according to the supplier both polymers are registered for use with isopropyl

alcohol, acetone, and most oils. In this study, two cleaning methods were used to prepare

the surface for spraying [24]. The first, used 99% ethanol and air-blasting, while the

second method used 99% Isopropyl alcohol and drying by natural convection. Both

methods and their effects on the adhesion strengths for both polymers will be examined

further in the report.

2.3 Thermal Spray Techniques and Coating Deposition

2.3.1 What is Thermal Spraying?

Thermal spraying is a material deposition process which can be achieved using several

different technologies. Typically, a high temperature heat source is used to melt or heat

particles of the desired coating material, which are then accelerated and focused in a fluid

stream through a spray nozzle directed at the selected substrate [12]. The heating

process supplies enough energy for the metallic particles to melt or soften and deform

upon impacting the surface of the substrate. A lamellar structured splat is formed on the

16

substrate surface, and any proceeding layer of molten particles will stack on the previous

deposit creating a metal coating [12]. The three most prominent methods of thermal

spraying are (i) flame, (ii) plasma, and (iii) electrical arc. These methods are named after

the heating method used, and characterized by their heat, mass, and momentum transfer

[12]. Flame spraying uses combustion as a heat source with temperatures ranging from

2000 to 3000 °C to melt and accelerate feedstock material towards the substrate. This

method is relatively inexpensive, but demands sensitive control as high thermal loads

may be experienced by the polymer substrates [12, 25]. Plasma spraying uses an ionized

gas jet that reach temperatures of 14,000 °C to melt and propel feedstock powder usually

between 160 and 2000 m/s onto polymer substrates. This method can efficiently deposit

metals with high melting temperatures; however, plasma spray metallization must be

careful carried out to avoid degradation of the substrates.

2.3.2 Thermal Spray Process: Twin-Wire Arc

Electric wire-arc thermal spraying is attractive for thermal spray coating in industrial

applications because of its low-cost operation, high spray rates, portability, easy-of-use,

and simplicity. Only compressed air is required to operate a wire-arc thermal spray,

without need of water or other gases [26].

Figure 2.5: Wire-Arc Thermal Spray Schematic

17

The electric wire-arc generates an electric arc discharge that can achieve temperatures

beyond 5000 °C with particle speeds up to 300 m/s [12, 26]. The spraying process is

depicted in Figure 2.5 above, where two feedstock wires of the same material are given

opposing electrical polarities and feed, at the same velocity, through a nozzle to create

an electric arc where the wires converge. Then, as the arc melts the two wires a carrier

gas, typically compressed air, atomizes the melted particles and accelerates them

towards a substrate [12, 26].

2.3.3 Spraying Apparatus and Procedure

A high-density arc spray coating system manufactured by Thermion (Model 57456,

Silverdale, Washington, USA) was used as the thermal spraying method for metallization

of Teflon® and Polyethylene. As illustrated by Thermion, the Jet Force AVD 456HD Arc

spray system can provide precise and continuous wire feed rates. The control unit is

equipped with digital volt and amp meters that are adjustable using dials located

underneath the appropriate displays [27].

Figure 2.6: Thermion Auto Arc, AVD 456-HD System on top of Miller Deltaweld® 652.

When performing any spray operation, all parameters of the wire-arc must be checked to

prevent overheating of the thermal spray nozzle and damaging of the unit. The required

voltages and currents for the specified spray metals are listed below in Table 2.3. These

parameters were kept constant consistent throughout all tests performed throughout this

report.

18

Table 2.3: Thermal Wire-Arc Spray Parameters [27].

Parameter Zinc Aluminum

Torch ValuArc 200 ValuArc 200

Atomizing Gas Dry Air Dry Air

Air Cap HV Cap HV Cap

Wire Feed Rate (m/min)

7 7

Input Voltage (V)

28 32

Input Current (A)

200 200

Inlet Pressure (Psi)

100 100

Spray Distance (in)

6 6

2.4 Adhesion Apparatus

2.4.1 PosiTest™ Adhesion Pull-Test Device

The PosiTest™ AT-M Manual Tester was manufactured by DeFelsko (AT-M, St.

Catherines, Ontario, Canada) [28]. This specific adhesion tester conforms to international

standards such as ASTM D4541/D7234/D7522/, ISO 4624/16276-1, AS/NZS

1580.408.5, and others [29]. As the tester uses a manual hydraulic pump, a pull-rate

indicator is displayed on the monitor to adjust the rate of pulling. There is an internal

memory for the device that can store up to 200 pull tests, which can be extracted to

DeFelsko desktop software (PosiSoft Desktop). The requirements to use the pull tester

are relatively in-expensive and the standard dolly size used in this research was the

ATM20 (20 mm aluminum dolly), however dollies of sizes 10, 14, and 50 mm can be used

depending on the requirement pressure. The device has a self-aligning feature as

illustrated in Figure 2.7. The adhesion tester provides a uniform pull-off force that will

remove the coating of the sample normal to the surface, regardless of the uniformity of

the coated surface [28, 29]. All pull tests will have a resolution of 0.01 MPa (1 psi) with an

accuracy of ± 1% [28, 29]. The preparation and pulling of the samples will be explained

in the next section, while maximum pull-of pressures are displayed in Table 2.4 below.

19

Figure 2.7: PosiTest AT-M20 Manual Adhesion Tester next to a prepared sample, and a diagram for the self-

aligning mechanism [28, 29].

Table 2.4: Maximum Adhesion Strength per Dolly Size for PosiTest Adhesion Tester

Dolly Size Max Pull-Off Pressure

10 mm 10,000 Psi 70 MPa

12 mm 6,000 Psi 40 MPa

20 mm 3,000 Psi 20 MPa

50 mm 500 Psi 3.5 MPa

2.4.2 Pull-Test Methodology

First, polymer samples are coated with either aluminum or zinc to an appropriate

thickness. Then, samples are examined for any signs of delamination and if any cracks

or lifting is noticed the samples will not be used for adhesion testing. Typically, several

passes will be examined where delamination is most likely to occur, and the samples will

be sprayed below that delamination limit. Once, appropriate samples have been selected,

20 mm aluminum dollies, will be sand blasted to improve adhesion. Devcon No.19770

‘plastic steel’ two-part epoxy (Model 19770, Aurora, Ohio, USA) is used to adhere the

dollies to the substrate. The epoxy begins to harden after 1 hour and reaches maximum

strength after 16 hours of rest [30]. Next, a 20 mm hole saw is used to isolate the area of

the dolly to limit the pull-off zone; without the hole saw larger areas may be pulled from

the sample increased the experimental error. Finally, the operator will check for the

appropriate settings, and begin to engage the hydraulic pump until the coating has been

removed.

20

2.5 SEM Imaging and Cold-Mount Polishing

2.5.1 Cold-Mounting and Polishing

Considerable caution must be taken when attempting to analyze interfacial features for

metal-to-polymer coatings. In this study, cold mounting was the procedure used as it is

the preferred method for temperature and pressure sensitive materials. In some cases,

the epoxy and hardener mixture can give off heat during solidification due to

polymerization, however the heat is not comparable to alternative methods of mounting

(i.e. Hot Mounting) [31]. The cold mounting method is typically lengthy but can be modified

depending on the requirements of the operator. First, the quality of the coated polymer

samples should be examined for any signs of delamination, the effects might develop

during the epoxy solidification process. Once, an appropriate sample void of

delamination, has been selected, it is cut with a diamond saw to the appropriate length

that would sit within the cold-mounting mold. A small plastic holder maintains the

orientation of the sample, while preventing delamination during the epoxy polymerization

process. Second, an EpoxiCure™2 hardener and resin are mixed together at a ratio of 1

parts hardener to 4 parts resin. Then, the epoxy mold is sprayed with a Sprayway®

Industrial Silicone lubricant to help release the hardened sample from the mold. Third, the

resin is poured in and around the epoxy mold holding the coated polymer. Finally, after

solidifying for 24 hours the sample is removed from the mold and is ready for the polishing

process. An AutoMet™ 250 Grinder-Polisher by Buehler® (Model 49-7257, Lake Bluff,

Illinois, USA) was utilized to acquire uniform polishing on the epoxy imbedded samples.

The grinder-polisher can be used either manually or automatically, however, to maintain

consistency in the preparation of the samples all tested polymers were prepared

automatically according to the machines requirements (see Figure 2.8 and Table 2.5).

Once, the machine has been turned on, the base and head speeds must be calibrated to

150 and 50 rpm, respectively. Then, the samples are placed inside the 6-piece holder

and placed just above the grinding plate. The grinding plate is selected and placed

manually by the operator; the order of grinding is listed below.

21

1. 240 Grit [P280] BuelhlerMet™2 Abrasive Paper

2. 320 Grit [P400] CarbiMet™ SiC Abrasive Paper




6. 1200 Grit [P2500] MicroCut™ Discs PSA Backed

7. 9 Micron [Water Base] Buehler Metadi® Diamond Suspension

8. 3 Micron [Water Base] Buehler Metadi® Diamond Suspension

9. 0.04 Micron Colloidal Silica, Precision Surfaces International Polishing Suspension

The grinding operations were completed for a 120 second cycle, and the samples were

rinsed with water to remove any debris remaining on the surface. Special consideration

was taken when moving to steps 7 to 9, where an appropriate plate (based on the micron

size) was selected in replace of the standard Buehler® base plate used from steps 1 to

6. Thus, after step 9, the sample is gently washed with water to reveal the glass-like finish

(see Figure 2.8), which is ready for SEM-Imaging.

Figure 2.8: (Left) Buehler AutoMet 250, (Right) Polished Sample: Al coated PTFE

22

Table 2.5: Buehler AutoMet 250 Polishing Parameters [32]

Parameter (units) Value

Machine Power (VAC, Hz, Phase)

100-240, 50/60, 1

Motor Power (W)

750

Platen Wheel Speed (RPM)

10-500

Operation Head Speed (RPM)

150

Operation Base Speed (RPM)

50

Head Rotation (CW/CCW)

CW

Base Rotation (CW/CCW)

CW

Specimen Load (Lbs [N])

6 [27]

Base Power Usage (kW, A @ VAC)

1.1, 9.6/4.8 @ 115/230

Base & Head Power Usage (kW, A, VAC)

1.73, 15/7.5 @ 115/230

Weight (kg)

77

2.5.2 Scanning Electron Microscopic (SEM) Imaging

Analysis of the topography of the interfacial surfaces of the samples was performed with

the Hitachi High-Tech TM3000 Tabletop Scanning Electron Microscope (see Figure 2.9).

The Hitachi system utilizes multiple features in order to establish focused optical images

of complex specimens [33]. Imagining of non-conductive specimens is priority for this

study and is optimized in this SEM system. Optical magnifications of x15 to x30,000 are

available with slight adjustments on the company supplied desktop interface. As the

substrates are non-conductive and white in colour, a conductive tape is attached to the

front and back of the samples in order to achieve higher resolution SEM images. After

placing the substrate in the center of the vacuum platform, the hatch is closed and air is

evacuated, beginning the scanning process.

23

Figure 2.9: (Left) Hitachi High-Tech Tabletop Microscope TM3000, (Right) Cold-Mounted Sample Centered in

SEM

2.6 Substrate Heating Methods

2.6.1 Wire-Arc Heating Apparatus

A heating unit that would be capable of reaching temperatures above the melting point of

the polymer substrates during a thermal spraying operation was constructed. This

apparatus consists of 4 major components: the heating block, heater cartridges, a

variable transformer, and a cover plate (see Figure 2.10). First, the heating block was

machined from a ½ inch thick low-carbon steel sheet. The steel sheet was cold worked

during fabrication to retain its hardness (Rockwell B80) with a general thermal

conductivity and coefficient of thermal expansion of 50.45 W/m·K and 13 x 10-6 per °C,

respectively [34]. The steel block was machined to hold 3 cartridge heaters to heat the

system to the desired temperature. The cartridge heaters were 2 inches in long with 1/8-

inch diameters and were rated for a maximum temperature of 760 °C. Power to the

heaters was controlled by a Powerstat® variable transformer that controlled the voltage

supplied to them. A constant current is supplied depending on the series of the Variac,

for the experiments performed in this report the series selected was Series 126 (120 Volts,

constant current of 15 A, and constant impedance of 20 ohms) [35]. Finally, to reduce

contact resistance with the polymer substrates, an aluminum cover plate was

manufactured to maintain a constant spray area and hold all sample firmly against the

heater block to prevent any bending that may occur due to thermal expansion.

24

Thermocouples are attached to the substrates through holes drilled in the heater block,

and thermocouple junctions were placed flush with the substrate surface. The

thermocouple bead diameters ranged from 0.80 to 1.00 mm. The thermocouples were

purchased from McMaster-Carr and are K-Type FEP insulated (+Jacket) 20 Gauge

(0.032 inch diameter) wires with maximum temperatures of approximately 200 °C and a

0.2 second response time [36].

Figure 2.10: Smooth PTFE Samples inside Heating Set-Up

Figure 2.11: POWERSTAT® variable transformer (Left) attached to 3 Heat cartridges (Right)

25

2.6.2 Substrate Surface Heating Equipment

Two methods were used to mimic the polymer substrate response to high temperature

distributions during thermal spraying. The first method utilizes the Despatch LAC series

2 forced air oven (see Figure 2.12) that can reach temperatures up to 260 °C [37].

Polymer samples are placed face up towards the ceiling of the furnace with all air vents

closed. Once the samples are heated for 5 minutes, they are examined under the

surfometer and SEM. The second method requires the MasterCraft 3-position heat gun

[38], which has two operation settings, low and high. The low setting reaches to

temperatures up to 260 °C, while the high setting reaches temperatures up to 400 °C.

The Mastercraft heat gun is mounted on a stand directly facing a polymer sample that is

mounted to the stand in Figure 2.10 with perforated sheet and metal wires.

Thermocouples are attached to the polymer substrate and monitored during testing to

ensure desired temperatures are reached and not exceeded.

Figure 2.12: Despatch LAC Series 2 Forced Air Oven, (Right) Mastercraft 3-Switch Heat Gun

26

2.6.3 Thermal Data Collection Set-up

All temperature measurements recorded and analyzed throughout this study was

performed using the data acquisition modulus (DAQ) purchased from Omega® (OMB-

DAQ-2408, Saint-Eustache, Quebec, Canada). The OMB-DAQ-2408 Series Multifunction

USB DAQ has sampling rats up to 1000 samples per second, with 16 single-ended (SE)

inputs and 8 differential (DIFF) 24-bit analog inputs [39]. These analog inputs come in 8

ranges from ± 10V down to ± 0.078 V (at factors of ½). This system is compatible with

two software programs that were used for all temperature recording sessions: InstaCal

and TracerDAQ. The first program, InstaCal was created by MC, measurement

computing™ as a software to detect and configure any DAQ hardware system connected

to a testing PC. The software can test the system both internally and externally, and is

supported by most operating systems (Window® 10/8/7/CP,32-bit or 64-bit) [40]. The

second program, TracerDAQ was also created by MC, measurement computing™ to use

in conjunction with InstaCal for data acquisition. The program can generate strip chat,

oscilloscope, function generator, and rate generators based on the user requirements.

The program can organize and display data, and provide different saving configurations

(.sch, .bin, .txt, and .csv), all data used in this report was saved as text in .csv and

exported into standard Excel files [41].

27

Chapter 3 Wire-Arc Deposition onto Polymers

Characterization of Metal-to-Polymer Adhesion

3.1 Introduction

This chapter focuses on characterizing the properties of both the metallic coated layer

and the polymer substrate. First, the properties of the deposited wires will be discussed

to introduce variables of interest that may prevent or support adhesion with the polymer

substrates. Second, using the mechanical treatment methodology developed in Section

2.2.3 the roughness of the polymer surfaces will be characterized for each consecutive

test, and the surface topography will be examined. Third, wire-arc coatings will be

deposited and examined using SEM imaging of the metal-to-polymer interface. Finally,

this section will conclude with adhesion data collected from the several tests performed

through this study (see Table 3.1 below).

Table 3.1: Overview of Metal-To-Polymer Tests

Test Polymer Substrate Surface Grit # Coating

1 PTFE Rough 20 Aluminum

2 PTFE Smooth 0 Aluminum

3 PTFE Rough 20 Zinc

4 PTFE Smooth 0 Zinc

5 HDPE Rough 20 Aluminum

6 HDPE Smooth 0 Aluminum

7 HDPE Rough 20 Zinc

8 HDPE Smooth 0 Zinc

3.2 Deposited Metal Wires

3.2.1 Properties of Metal Coatings

The mechanical and thermal properties of both aluminum and zinc may contribute

significantly to the strength of adhesion on a polymer substrate. The properties will be

illustrated below in Table 3.2, along with a standard range of bond strengths provided by

the manufacturer Oerlikon Metco, of the metal deposited onto grit-blasted steel substrate.

28

Table 3.2: Mechanical, and Thermal Properties of Aluminum and Zinc [42, 43]

Properties (unit) Aluminum Zinc

Density (g/cm3)

2.41 6.36

Composition (%) 99.5 Al (0.5 other) 99.9 Zn (0.1 other)

Diameter (mm) 1.42 1.62

Thermal Conductivity

(W/m·K)

210 112

Thermal Expansion Coefficient (x 10-5 K-1)

2.31 3.02

Specific Heat Capacity (J/g·°C)

0.9 0.39

Melting Point (°C) 660 419

Bond Strength (MPa)

[On Rough Steel]

7.0 – 30.0 6.9 – 15.0

According to Gonzalez et al. [12], deposition of metal bond-coats are required when

depositing high melting point metals such as aluminum. As stated above in Table 3.2,

aluminum melts at around 660 °C. However, due to strong exothermic oxidation that is

promoted by the pressurized air jet and the small size of the droplets (roughly 30-40 µm)

the temperature of the particles is believed to be higher than the melting temperature. In

the case of PTFE, with a thermal decomposition temperature of 470 °C, metal bond coats

with lower melting temperatures such as zinc may be better in achieving adhesion with

plain polymer substrates. Chen et al. [44], successfully sprayed a 400-700 µm layer of

zinc onto untreated and grit-blasted ABS substrates which possess similar molding

temperatures (glass-transition range) of HDPE. Since Chen et al [44], have demonstrated

that zinc can adhere to plain thermoplastic amorphous polymer like ABS, adhesion on

HDPE and PTFE will be examined.

3.3 Surface Roughness

3.3.1 Uniform Roughness Profiles

As previously stated in Section 2.2.3, samples were prepared using the grit size 20

aluminum oxide blasting media, sprayed at 100 kPa. The arithmetic mean roughness (Ra)

values are presented for the first 20 samples of HDPE and PTFE in Figure 3.1; all

29

subsequent samples showed similar trends for surface topography and roughness. The

mechanical treatment methodology was able to produce Ra values of roughly 1.60 ± 0.05

µm with the 20 sized aluminum grit. The polymers received from McMaster-Carr had Ra

values, along the direction of spraying, of approximately 0.20 ± 0.05 µm. Furthermore,

throughout the remainder of this study, all samples mechanically treated to the

appropriate Ra value will be considered rough (labelled #20), whereas all samples

provided by the manufacturer will be considered smooth (labelled #0).

Figure 3.1: Uniform Substrate Surface Roughness Averages (0 = Smooth, 20 = Rough)

The roughness averages presented in the figure above, demonstrate the consistency of

the generated mechanical treatment methodology.

3.3.2 SEM-Images of Surface Topography

Analysis of the substrate surfaces before and after mechanical treatment was done to

determine the existence of any polymer ‘damage’. As the roughness values for both PTFE

and HDPE were within ± 0.05 µm for both the smooth and rough surfaces, examination

of the microstructure was performed to understand the topography of each specimen.

30

Figure 3.2: x200 magnification SEM-Image of PTFE/Teflon®, Smooth (A) and Rough (B)

Figure 3.3: x200 magnification SEM-Image of HDPE, Smooth (A) and Rough (B)

Figure 3.2 (A), shows a smooth PTFE surface provided by the manufacturer at Ra values

of roughly 0.20 µm. The surface prior to mechanical treatment is clear of liquid or solid

contaminants. Any water remaining on the surface dried at room temperature, and

contaminants such as grease and dust were cleaned using a 99% isopropyl wash. As the

specimen was produced through a skiving process small lines can be seen that are

directly correlated to the flatness of the extrusion blade in the manufacturing process.

These small lines do not interfere with the overall surface roughness but may play a small

role in overall adhesion. In contrast, for Figure 3.2 (B) the roughened surface averages

at an Ra value of approximately 1.60 µm. The small white particles seen in the SEM-

image, of Figure 3.2 (b) are embedded aluminum oxide abrasive media, that reduce

31

overall adhesion between the polymer and metal coating. Valleys and peaks have

appeared on the roughened sample which will aid in mechanical interlocking and lead to

higher adhesion strengths.

Similar results as the PTFE sample can be witnessed for the HDPE in Figure 3.3 above.

The smooth HDPE substrate is seen in Figure 3.3 (A) where the skiving patterns similar

to that in Figure 3.2 (A) can be observed. The magnitude of the skive marks are slightly

higher than that of the smooth PTFE surface, and will be considered when examining

adhesion strength with the metallic coatings. However, as the overall roughness average

evaluated along the spray direction, parallel to the skive imprints, remains within the

smooth criteria the sample is considered suitable for metallization. Only a few dust

particles are observed on the substrate, along with a few indentations from handing the

specimen, that will be cleaned using the same procedure as described for smooth PTFE

samples. Conversely, the rough sample HDPE sample in Figure 3.3 (B) exhibits a similar

average roughness as the rough PTFE sample in Figure 3.2 (B) however, there is

significantly more residue remaining after the mechanical treatment. Additional

consideration must be taken when chemically cleaning and preparing the samples for

metallization.

3.4 Thermal Wire-Arc Coatings

3.4.1 Coating Deposition and Limitations

Thick zinc coatings of approximately 260 µm were obtained on all PTFE and HDPE

samples, regardless of the specimen’s surface Ra value. Aluminum coatings were

obtained on the smooth and rough PTFE substrates, but the coatings delaminated from

HDPE substrates within the first two passes of the wire-arc spray. The coating deposition

rate for these tests will be measured by the increase in coating thickness per pass of the

wire-arc spray, as the samples are significantly smaller than the spray area of 1 total pass

(Sample Area = 25.81 cm2). The deposition rates for the smooth virgin specimens and

their mechanically treated counterparts vary slightly, as the roughened surfaces will

capture a higher volume of metal on the first pass. The coating thickness per pass of the

spray are listed below.

32

Table 3.3: Coating Deposition Per Pass on Rough & Smooth Polymer Surfaces

Substrate Coating Coating Deposition (µm per pass)

PTFE Al 44.0 ± 1.00

PTFE Zn 37.0 ± 1.00

HDPE Al 0

HDPE Zn 38.0 ± 0.50

For consistency within the adhesion pull tests, all tests were performed once the overall

coating thickness had reached 260 ± 10 µm. Therefore, 6 passes of aluminum spray and

7 passes of the zinc spray were enough to reach the desired coating thickness. If any

alterations to the coating was performed, it will be illustrated in subsequent section of this

study, along with the coating deposition per pass.

Figure 3.4 and Figure 3.4 are SEM images of the coating surfaces of aluminum and zinc

respectively. For consistency, only coatings on roughened PTFE will be examined. The

calculated porosity for the following sections is dependent on the polishing procedure

after cold mounting the coated samples. The number of detectable pores will increase as

the polishing process is further refined. All porosity measurements and calculations can

be found in Appendix A.

Figure 3.4: (Left) SEM Cross-sectional View of ~260 µm thick aluminum coating onto roughened PTFE,

(Right) ImageJ processed visualization of pores (white) on the top surface of the coating (black).

In Figure 3.4, the thick aluminum coating completely covers the entire PTFE substrate,

and exhibits interesting splat behaviors. According to Hale et al. [45] , in the study of in-

flight particle measurements for aluminum particles, the average size of the particles

33

projected from a thermal wire-arc would be 33 to 53 µm, and splats with diameters ranging

from 100 to 400 µm can be observed on the outer most layer. Porosities of the coating

must also be evaluated, according to Oerlikon Metco, the supplier of the wire-arc and

coating material, the typical porosity of aluminum coatings should be 1 - 2 vol.% [43].

However, the porosity of the coating was by examining an imaging processing software,

ImageJ. SEM images were taken of the coating cross-section and it was determined that

the porosity based was approximately 10 ± 2.5 %. This porosity result is expected to

remain consistent throughout the report, as the spraying parameters will remain

consistent in all tests.

Figure 3.5: (Left) SEM Cross-sectional View of ~260 µm thick zinc coating onto roughened PTFE, (Right)

ImageJ processed visualization of pores (white) on the top surface of the coating (black).

The zinc coating on roughened PTFE is shown in Figure 3.5. According to Johnston et

al. [46], air-borne zinc droplets at the appropriate arc current and air pressure can have

particle diameters varying between 28 – 37 µm. However, in the SEM of the zinc topcoat,

it can be noted that splats with diameters of 50-250 µm are produced. The existence of

these splats is predicted to be caused by similar effects experienced in the aluminum

coating. The main cause of increase droplet size would be splashing due caused by low

substrate temperatures and molten droplet accumulation on the substrate surface. The

porosity is predicted to be higher than that of the aluminum coating by Oerlikon Metco,

approximately 4 vol.% [42]. Using ImageJ, the porosity determined by analyzing the

cross-sectional areas was roughly 4.8 ± 1.1%. However, this porosity percentage will vary

34

based on the degree of polishing done to the cold-mounted sample. Refining the polishing

process will increase the number of visible pores in the cross-sectional view, therefore

the calculated porosities are estimates of the overall coating.

3.4.2 SEM-Images of Coating Interface

In this section, samples from tests 1 – 8 illustrated in Table 3.1 will be cut, and polished

to examine their interfacial features. The SEM described in Section 2.5.2 will be used to

understand any significant differences or patterns that may contribute to enhancing or

reducing adhesion capabilities between the metal coating and polymer substrate. SEM

images of the metal-to-polymer interface will be presented below, followed by an

explanation of any notable features or properties that should be highlight for analysis.

First, comparisons between zinc coatings and aluminum coatings will be made on a

roughened PTFE surface, as coatings were not achievable with aluminum onto HDPE.

35

Figure 3.6: x250 Magnification Overview (OV1-2) SEM images of ~260 µm Thick Coating Aluminum onto PTFE (20), Along with x1.0k Magnified Images (A-D) of Specified Interlocking Mechanisms.

The SEM image in Figure 3.6 (OV1 & OV2) captures interesting features in the interface

between the metal and polymer. The image does reveal evidence of micro-scaled

delamination that was not visible prior to cold mounting. The existence of small pores or

36

cracks may come from the coating process as wire-arc deposition typically results in

highly porous coatings.

Nevertheless, it can be observed that a large amount of interlocking has occurred

between the metal and polymer substrate. Figure 3.6 (A to D) closely examines

significantly deeper interlocking that occurs throughout the length of the boundary. The

existence of these deep interlocking areas will greatly increase the overall adhesion

strength between the coating and substrate. Additionally, from images (B) and (C) in

Figure 3.6, the deep interlocking suggests that the metal coating may be flowing deeper

into the polymer substrate, as the overall temperature of the system increases. If the

sample was polished further, image (B) would expose the complete metal link witnessed

in the image, this is evident as for image (C) the interlocking completely encapsulates the

polymer substrate. Images (A) and (D) represent typical cases of mechanical interlocking

that is witness on metal-to-metal surfaces after thermal coating, however image (D) does

support the suggestion of polymer flow, as witnessed in images (B) and (C). Finally, the

entire length of the boundary shows signs of minor and major interlocking occurring

between the metal and polymer that will increase the adhesion strength of the overall

thick coating.

37

Figure 3.7: x250 Magnification Overview (OV1-2) SEM images of ~260 µm Thick Zinc Coatings onto PTFE (20),

Along with x1.0k Magnified Images (A-D) of Specified Interlocking Mechanisms.

38

Similar to the interlocking mechanisms found between the aluminum coated rough PTFE

in Figure 3.6, interlocking also occurs with the zinc coated roughened PTFE samples,

thought to a lesser extent. In Figure 3.7, four areas were examined for the interlocking

phenomena and overall boundary adhesion condition. Immediately, it should be noted

similar patterns of micro-delamination can be observed on the coating-to-substrate

interface. These patterns would most likely arise due to similar reasons, previously

discussed for the aluminum coated samples, delamination due to the coating process and

polymerization during cold mounting. However, and more importantly, the microscopic

imaging reveals that the amount of interlocking occurring at the interface between metal

and polymer is significantly lower than with the aluminum coating. This observation may

result in a lower adhesion strength with the zinc coated polymers, which may provide

evidence that temperature plays a significant role in the adhesion process between metal

coatings and polymer substrates. In Figure 3.7, images (A) and (B) show deep

interlocking zones that were similar to the zones found on the aluminum coating in Figure

3.6. However, the interlocking found on the zinc coated images (A) and (B) suggest that

the particles adhered to the surface at significantly colder temperatures than that of

aluminum which represents the properties as mechanical interlocking. Chen et al., [44]

produced zinc coated ABS coupons using an electric wire-arc and presented a similar

interlocking phenomenon. However, in their results adhesion was further promoted by an

increased surface roughness in the polymer substrate which resulted from the 3D printing

manufacturing process. The overall interlocking achieved by Chen et el, was similar to

that of images (C) and (D) in Figure 3.6 where micro level adhesion occurs between the

metal and polymer substrate, but without the deeper hooks found with the aluminum

coating. Thus, according to Table 3.2, the temperature of the impacting zinc particles may

play a significant role in the existence of these deep hooks.

3.5 Adhesion Pull-Test Results and Analysis

3.5.1 Polymer Sample Data

Adhesion pull-tests were performed on samples from tests 1-8, that achieved

approximately 260 µm thick coatings, and that did not show delamination. The data of all

adhesion tests performed can be found in the figure below.

39

Figure 3.8: Adhesion Strength Pull-Test Data on Tests 1-8.

Figure 3.8 presents the adhesion strength data for all the tests with the blue bars

representing zinc coated samples and the orange representing aluminum coated

samples. The error bars in the figure represents the standard deviation from the average

determined from the pull tests performed on 5 samples. Therefore, a total of 40 samples

were tested, of which only 30 achieved a metal coating. Additionally, all substrates are

labelled on the x-axis starting with smooth PTFE and ending with Rough PE. On the

smooth PTFE samples the wire-arc spray was able to deposit thick aluminum and zinc

coatings.

The zinc coating onto smooth PTFE with an Ra value of approximately 0.20 µm had an

adhesion strength of 0.43 MPa. In comparison, the aluminum coating on the same

substrate had almost double the adhesion strength, approximately 0.76 MPa. The

aluminum coating has significantly higher adhesion strength than the zinc on the same

substrate, which is most likely induced by the higher degree of mechanical interlocking.

Additionally, this trend is exhibited on the mechanically treated PTFE samples with an Ra

value of about 1.60 µm. The zinc coated rough PTFE exhibited an adhesion strength of

about 0.85 MPa, and the aluminum coated sample produced roughly 1.37 MPa. The

40

aluminum coating generated almost double the adhesion strength than the zinc

specimen, and the mechanical treatment of the substrates increased overall adhesion in

both the aluminum and zinc coatings. The adhesion strength of the zinc coating increased

by 98% (factor of 2.0) when introducing mechanical treatment, and the aluminum coating

by roughly 80% on PTFE samples. Thus, introducing a roughened surface increased the

overall hooking phenomena evaluated in Section 3.4, which resulted in a significant

increase in the overall adhesion strength of the system regardless of the metallic coating.

For the HDPE samples, the coatings demonstrated similar results with a contrast to the

aluminum tests. All smooth HDPE samples had an Ra value of approximately 0.20 µm

and their rough counterparts, an Ra of roughly 1.60 µm. Now, thick zinc coatings were

achieved on both smooth and roughened HDPE, however aluminum was unable to

adhere regardless of the surface preparation. The zinc samples produced adhesion

strengths of roughly 0.49 MPa and 0.72 MPa, on the smooth and roughened samples

respectively. The increase in adhesion strength contributed by the mechanical treatment

is present in the HDPE samples, at approximately 47 % increase from the smooth sample

to the roughened sample. Nevertheless, mechanical treatment of both polymers resulted

in higher adhesion strength.

Table 3.4: Adhesion Test Results of Aluminum and Zinc Coated, PTFE and HDPE ( "0" = delaminated)

Substrate PTFE/Teflon® HDPE

Smooth Rough Smooth Rough

Zinc 0.43 0.85 0.49 0.72

Aluminum 0.76 1.37 0 0

3.5.2 Sample Delamination

The HDPE substrates experienced delamination between the first and second pass of the

electric wire-arc. The SEM image below in Figure 3.9 illustrates aluminum delaminating

on a roughened HDPE, and an SEM image of the substrate after removing all delaminated

aluminum pieces.

41

Figure 3.9: SEM-image of aluminum delamination on right, and on left a photo of the delamination specimen.

It should be noted that in Figure 3.9, droplets have deposited onto the specimen roughly

where there were peaks and valleys generated by the mechanical treatment. However,

one very important feature should be recognized between the delaminated sample and

the mechanically treated one presented in Figure 3.3. Specifically, in the smooth HDPE

surface the presence of grooves generated through the skiving process used by the

manufacturer vanish upon mechanical treatment. However, these grooves are faintly

observed after delamination of aluminum, which suggests that the sample becomes

smoother after thermally spraying the aluminum. As aluminum is at a significantly higher

temperature than zinc, especially due to the rapid oxidation of the air-born aluminum

particles, the HDPE may be melting during deposition causing delamination of the

coating.

42

3.5.3 Results and Discussions

All presented in section 3.1 were evaluated using SEM imaging of the interface between

the metallic coating and polymer substrate. From these eight tests, the following results

were achieved.

• A thick aluminum coating on smooth PTFE was obtained

• Aluminum was not able to adhere to HDPE

• Aluminum coatings have roughly double the adhesion strength of zinc,

regardless of the substrate roughness.

• Mechanical treatment of the polymer substrates enhanced the adhesion

strengths of all tests

• Mechanical treatment of HDPE did not aid in achieving an aluminum coating

The results of the microscopic imaging and adhesion tests had suggested that the

temperature of deposition and substrate may play significant roles in promoting or

reducing adhesion capabilities. As discussed in section 3.4.2, a significantly higher

degree of hooking may have been influenced by metal deposition close to the glass-

transition temperatures of the polymer substrates where there was enhanced mechanical

interlocking induced by flow of the polymer substrate. Temperature measurements and

examination at elevated substrate temperatures must be conducted to determine if there

are any thermal influences on metal-to-polymer adhesion.

43

Chapter 4 Coating onto Heated Substrates

Temperature Analysis of Wire-Arc Deposition onto Polymers

4.1 Introduction

Results have shown that a thick coating of aluminum can be deposited on PTFE, in

contrast to HDPE where, regardless of surface preparation, aluminum will not adhere.

However, zinc coatings are obtained on both polymers and no delamination is seen on

the smooth HDPE and PTFE substrates. The polymers have similar thermal properties;

however, PTFE has a glass-transition temperature of 115-125 °C and HDPE has a

maximum operation temperature of roughly 80 °C. Additionally, the HDPE surface

experiences melting around 125 – 138 °C, suggesting that the PTFE begins to experience

plastic behavior while HDPE begins to melt. Results in Chapter 3 have suggested that

aluminum coated PTFE experiences a high degree of hooking, which may be a result of

deposition near the glass transition of the material. Thus, this section will examine the

influence of manipulating substrate temperature to determine the associated effects on

metal-to-polymer adhesion.

First, temperature measurements will be collected with 4 K-type thermocouples capable

of a 0.2 second response time connected to a DAQ as described in Section 2.6.3. As

mechanically treated and smooth polymer substrates will experience the same

temperature profile, only temperature measurements on the roughened samples will be

taken. Once the temperature data is acquired during deposition of zinc and aluminum

coatings onto both substrates, observation of the substrate topography will be conducted

with a 2-mode thermal spray gun and furnace, at temperatures simulating spray

conditions. Then, adhesion pull-tests will be conducted on all samples listed in Table 3.1

at elevated substrate temperatures. Specifically, rough and smooth PTFE samples will

be heated slightly below the glass transition temperature of 115 °C, and HDPE will be

heated to between 40-50 °C, half of the maximum operation temperature instructed by

the manufacturer. Cross-sectional SEM images of the interface between the heated

44

substrate and metallic coatings will be compared to the room temperature SEM images

presented in Section 3.4.2.

Figure 4.1: A typical temperature profile for Electric Wire-Arc Spraying using a Guided Arm

Figure 4.1 above, represents a zoomed in temperature profile of one complete pass of

the electric-wire arc torch over a substrate initially at room temperature that is sprayed

with aluminum. All figures examined later will have compressed profiles, because of the

increased number of passes shown. The temperature profile has been divided into 4

sections, starting off with section (A) pre-spraying conditions. In (A), the substrate

temperature prior to thermal spraying will be illustrated to define the heated or room

temperature samples. Then, section (B) presents a sudden increase in temperature

induced by introducing the air jet and electric arc within 6 inches of the sample surface.

The temperature of the substrate reaches a maximum during deposition in section (C),

and temperature fluctuations are observed that represent alternate heating and cooling

caused by progressive passes of the guiding arm for the wire-arc spray gun. The 3 peaks

will be consistent throughout the temperature profiles as the number of passes the guiding

arm requires to obtain 1 full coating on the polymer samples. Finally, Section (D)

illustrates the cooling phase between spraying, additionally, examination of any signs of

delamination is performed at this time. The time for cooling between samples vary based

on the heated and room temperature substrates and will be defined for each test.

45

4.2 In-situ Temperature Measurements during Thermal Spraying

The temperature data presented below is for mechanically treated substrates initially at

room temperature. Upon examination, it was determined that differences between smooth

and rough samples were negligible. However, the temperature profiles of the smooth

specimens will only be examined if there are any significant changes to the

measurements. Additionally, both smooth and mechanically treated temperature

measurements and figures can be found in the appendices.

4.2.1 Thermal Spraying: Aluminum onto PTFE and PE

Figure 4.2 shows the temperature variation of the roughened PTFE/Teflon® surface

during ten passes of the wire arc spray torch depositing aluminum.

Figure 4.2: Temperature data of a 10 Pass Electric-Wire Arc Deposition of Aluminum onto Roughened PTFE

Substrate at Room Temperature

First, the substrate starts at an atmospheric temperature of approximately 25 °C, then

during the first pass, as aluminum is deposited onto the polymer surface temperatures

reach a maximum of approximately 86 °C. A constant cooling period of 2 minutes is

maintained between coatings to permit complete solidification of the most recently

deposited layer. The minimum temperature after the cooling period of the first pass was

roughly 33 °C. However, with each proceeding pass of the spray gun there exists residual

46

thermal energy prior to the next coating. This residual thermal energy stabilizes within the

testing parameters between the 3rd and 4th coating. The maximum achievable

temperature during the testing period was recorded as approximately 88 °C, with a

minimum resting temperature after cooling of roughly 39 °C. All recorded temperatures

have exhibited behavior within the maximum of 88 °C, similarly the minimum temperature

after cooling maintained at roughly 39 °C on the 10th and final pass for the test. Finally,

similar results were obtained for the PE samples, however a complete aluminum coating

was not achieved.

4.2.2 Thermal Spraying: Zinc onto PTFE and HDPE

Figure 4.3 illustrates a ten-pass coating process of zinc deposited on a roughened

PTFE/Teflon® surface. Deposition on the HDPE samples will not be examined, as the

thermal properties are like that of PTFE, besides HDPE having double the specific heat

of PTFE. However, the deposition of zinc onto HDPE can be found in Appendix B.

Nevertheless, some discrepancies in the temperature measurements will be described

further in the explanation.

Figure 4.3: Temperature data of a 10 Pass Electric-Wire Arc Deposition of Zinc onto Roughened PTFE

Substrate at Room Temperature

47

Similar to the previous specimen in Figure 4.2, the test begins at an atmospheric

temperature of approximately 24 °C, then as the first coating of zinc is deposited onto the

polymer the temperature reaches roughly 36 °C. As the maximum temperature of the

substrate while depositing zinc is lower than the maximum temperature during aluminum.

Additionally, as zinc has a lower thermal conductivity than aluminum and the peak

temperatures during deposition are relatively low, the cooling period was adjusted to

roughly 30 seconds between passes. The minimum temperature achieved after the first

pass was roughly 27 °C, almost 3 degrees higher than ambient temperature. Patterns like

that of the aluminum deposition is observed while spraying zinc onto the polymer

substrates. The minimum temperature after the cooling phase, and maximum

temperature upon deposition of the metal gradually increases with proceeding passes.

The highest temperature, obtained at the 8th pass was roughly 44 °C, and the maximum

temperature after cooling obtained at the 10th and last pass was approximately 34 °C.

Thus, the polymer substrates are experiencing significantly different thermal cycling when

depositing zinc or aluminum. Although the temperatures of the substrates after cooling

only vary by 4-5 degrees, the maximum temperature experienced during deposition of

aluminum is almost double that when depositing zinc. Returning to results of chapter 3,

zinc has little trouble adhering to both polymer substrates, however, regardless of surface

preparation aluminum was not able to adhere to the HDPE. Thus, using the temperature

profiles examined above, the polymer substrates will be heated with two different methods

that mimic the thermal spray conditions.

4.3 Polymer Substrate Topography: Furnace Heated

In this section, examination of the polymer surface topography using SEM was conducted

for two heating tests. These two tests will attempt to characterize any surface differences

or changes in surface morphology using surface roughness testing.

4.3.1 Furnace Heated: Surfaces of PTFE/Teflon®

First, to determine the effects of surface heating during aluminum deposition, samples of

PTFE and HDPE were mechanically treated and placed within a furnace (see Figure 2.12)

at a resting temperature of 90 °C. Then, the samples were placed horizontally inside the

furnace for 30 minutes. Placing the samples horizontally prevented any gravitational

48

effects that may displace some of the polymer substrate while heating. After 30 minutes,

the substrates were taken out and immediately tested to determine their average Ra

values.

All SEM-images below were captured at relatively the same location, additionally all

figures will be organized under the same testing specimen. Specifically, if a figure

examines the virgin surface of a polymer, mechanical treatment of the polymer will be

conducted, and examination will be performed at the same location to maintain accuracy.

Each proceeding image will be the next step in the samples testing method (i.e. a PTFE

sample will be purchased as virgin smooth, then mechanically treated, and finally heated).

Figure 4.4: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin PTFE, and Smooth

Furnace Heated PTFE

49

The first observation from Figure 4.4 is the skiving pattern obtained during processing of

the material sheet. These patterns do not impact the roughness of the surface but aid in

observation of topography changes on the substrate after furnace heating. Nevertheless,

when comparing the virgin sample to the furnace heated counterpart no differences can

be observed. The average roughness values of the virgin samples were roughly 0.22 µm,

and after heating for 30 minutes at 90 °C, the resulting Ra value was 0.20 µm, both with

a 0.02 µm deviation. Thus, the temperature alone had negligible effects on the surface

roughness under thermal spray conditions.

In the next test, the virgin smooth PTFE sample illustrated in Figure 4.4, has a noticeably

higher roughness average. The roughness of the previous smooth samples was

approximately 0.22 ± 0.02 µm, but for the smooth samples for this specific test the Ra

values were roughly 0.68 ± 0.03 µm. This increase in virgin roughness is an uncontrollable

variable resulting from discrepancies in the manufacturing process. The discrepancies

have created a deep wave-like pattern on the virgin polymer substrate that has

contributed to the overall surface roughness. However, as these samples will be

mechanically treated, the roughness of the virgin polymer will not affect the analysis of

the test.

50

Figure 4.5: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin PTFE, Sandblasted

Rough PTFE, and Furnace Heated Rough PTFE

51

The relatively smooth PTFE samples are taken and mechanically treated with aluminum

abrasive, which result in samples with RA values of 1.58 ± 0.06 µm. Small white particles

can be observed on the ‘sand-blasted’ SEM images, which are residual sand and dust

from the surface treatment. These samples are then placed in furnace and allowed to

heat for 30 minutes at 90 °C, resulting in the ‘Heated + SB’ SEM images. The PTFE

roughened substrate experienced negligible changes to the surface roughness and

observed topography. Specifically, the roughened samples were scratch tested and

determined to have RA values of approximately 1.54 ± 0.06 µm.

4.3.2 Furnace Heated: Surfaces of HDPE

The HDPE substrate will be examined in this sub-section. Furthermore, all results

determined for both polymers will be summarized at the end of Section 4.3.3.

Figure 4.6: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin HDPE, and Smooth Furnace Heated HDPE

52

The tests performed on the roughened and smooth PTFE samples of the last section,

were repeated for the HDPE samples under the same conditions. This surface

examination will attempt to reveal temperature influences on the HDPE polymer, in

contrast to the negligible effects on the PTFE.

Accordingly, in Figure 4.6, SEM imaging of the surface topography of the smooth virgin

HDPE and smooth furnace heated HDPE are presented. All images in the figure above

will focus in the same relative area, specifically an observable ripple in the substrate

surface. First, it was observed that the non-heated virgin HDPE clearly defines the

irregularities in the rippling area. Additionally, this distortion in the polymer runs parallel

to the skiving patterns which are visually distinguishable when examining the surface at

400x magnification. Measuring the roughness parallel to the surface irregularities, the Ra

value was determined to be approximately 0.16 ± 0.01 µm.

Then, the smooth virgin samples were heated under the same conditions previous

described (30 mins at 90 °C) for the PTFE samples. The first noticeable difference in the

SEM images between the non-heated and heated surfaces is that the ripple and skiving

patterns are less visible under similar SEM parameters. The main stem of the ripple,

which is parallel to the skiving patterns, remains detectable, however, many of the smaller

features illustrated in the non-heated images become undetectable. Despite these

observations, the average roughness value for the heated substrates were roughly 0.15

± 0.01 µm. Therefore, although the analysis of the SEM imaging provided some evidence

that HDPE may be subject to softening at elevated temperatures, the roughness tests

deem the results inconclusive. The investigation of the mechanically treated substrates

may provide enough evidence on this claim.

53

Figure 4.7: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin HDPE, Sandblasted

Rough HDPE, and Furnace Heated Rough HDPE

54

A new smooth virgin HDPE sample was selected to examine the surface topography at

elevated temperatures. First, in Figure 4.7, surface images of the smooth virgin sample

were captured to highlight skiving patterns and any discrepancies that may be used to

distinguish between the surface preparation methods. Additionally, it should be noted that

the prevalent feature of the virgin samples; the skiving pattern, has proven present in all

tested polymer specimens. Diagnosis of the virgin surface roughness provided an Ra

value of roughly 0.24 ± 0.01 µm, parallel to the skiving pattern. Although slightly higher

than the roughness of the previous sample, the difference is negligible after mechanical

treatment.

The sand-blasted samples contain small ripples and debris, generated by the aluminum

oxide abrasive, that will be used to interpret any changes in surface topography. All

skiving marks, indicating smooth regions of the polymer, prior to mechanical treatment

have vanished and been replaced with the course and rugged exterior, expected of

sandblasting. Furthermore, the roughness average of the mechanically treated HDPE

substrates was 1.59 ± 0.06 µm, virtually identical to the sand-blasted PTFE samples.

Finally, after heating the samples for the specified time and temperature, the heated SEM

images were produced. However, similar conclusions to the smooth heated HDPE are

examined in the topography. Very little can be concluded besides small signs of softening

at the rippling areas, but there is a significant change in the overall roughness. The

evaluated Ra value for the rough heated HDPE was approximately 1.31 ± 0.05 µm, almost

0.28 µm lower than the non-heated rough samples. This decrease in roughness is roughly

18% lower than the roughened surface but is the highest change in topography examined

out of all tested samples. The influence of elevated temperatures does influence

roughened PTFE surfaces, but is this effect is difficult to detect in an isolated environment.

55

4.3.3 Furnace Heated: Results and Discussion

The figure below summarizes the roughness data acquired in the tests performed in

Sections 4.3.1 and 4.3.2. Each test was performed with 3 different samples, which were

all characterized at the virgin, sand blasted, and heated conditions. The roughness data

for each test can be found in Appendix C.

Figure 4.8: Evaluated Ra Values of Various Polymer at virgin, sand blasted, and heated conditions. Heating

Method: Furnace. (0 – Smooth, 20 – Rough)

In Figure 4.8, roughness data is separated in order of the tests performed starting with

the rough samples (#20) of a specified polymer, then the smooth samples (#0).

Additionally, the small error bars on top of the colored bars indicated the standard

deviation of 9 measurements per sample in a set of 3 per test. Furthermore, the black

bars represent the roughness of the virgin polymer purchased from McMaster-Carr [18,

19], the gold bars represent sand blasted samples, and the red represents the roughness

of heated samples. Now, as previously stated, the roughness of the PTFE 20 sample

prior to mechanically treating was significantly higher due to the existence of waves

created by errors in the manufacturing process. However, after mechanically treating the

surface via sandblasting, the overall roughness of the PTFE 20 was identical to the sand

blasted HDPE 20. The conclusions reached from the furnace heating test were:

56

1. No noticeable changes to surface topography and roughness were

observed for the PTFE samples, regardless of surface preparation.

2. Smooth Heated HDPE displayed small noticeable physical changes in the

surface topography that had no effect on overall surface roughness.

3. Heating a Roughened HDPE specimen in an isolated environment resulted

in approximately 18% reduction of surface roughness.

The examination of the influence of temperature on the smooth and roughened polymer

surfaces provided evidence of small surface changes that governs the need for further

investigation. As these tests were performed in an isolated environment, where only

temperature was the governing variable for surface alterations, the influences of the air-

jet and metal droplet impingement were omitted. An alternate test that evaluates the same

parameters examined above was constructed using a MasterCraft™ 3-Position Heat

Gun. This new test will mimic similar temperature conditions like the electric wire-arc,

while providing a low air-jet impingement on the substrate surface.

4.4 Polymer Substrate Topography: Heat Gun

4.4.1 Heat Gun: Temperature Measurements and Air Jet Impingement

Furnace heating the polymer substrates provided information on the effects of

temperature on polymers, now, this section will focus on using a MasterCraft™ 3-Position

heat gun to determine the effects of substrate heating via a heated air jet. The heat gun

has built in fans that will be used to mimic the wire-arc’s air jet, however at a lower air

velocity.

Now, a brief explanation of the typical temperature profile that will be experienced by the

polymer substrates via the heat gun will be provided below. This specific test was

performed on roughened HDPE; however, all tests have experienced similar temperature

profiles with negligible variations. Temperature data along with roughness data for the

preceding section can be found in the Appendix C.

57

Figure 4.9: Standard Temperature Profile for All Heat Gun Tests performed on Smooth PTFE Substrate

In Figure 4.9, the temperature profile of 5 heating intervals are examined starting at an

ambient temperature of approximately 23 °C. These heating intervals will mimic the

heating and cooling periods experienced by the electric wire-arc during deposition.

Generally, the heat gun will attempt to heat the substrate for roughly 14 seconds, this is

the approximate time it takes to reach the first peak of roughly 84 °C. The cooling phase

will be maintained at roughly 2 minutes in between each heating interval, this will allow

the temperatures to reach below glass transition for PTFE and below melting for HDPE.

In this specific test, the only discrepancy from the remaining temperature profiles, is the

reduced cooling phase in the first heating interval. However, this can be ignored, as the

profile is for smooth PTFE which has proven to show negligible affects below its glass

transition temperature evaluated during furnace testing. Nevertheless, the temperature of

the substrate immediately after the first cooling phase is roughly 55 °C, and the

temperature increases by 3 degrees to 58 °C at the final cooling phase. Additionally, from

the first heating phase to the last there is an increase of roughly 10 degrees resulting in

roughly 94 °C. These heating results will vary depending on the polymer; however, the

overall patterns will remain the same. Furthermore, these temperature profiles replicate

the nature of the temperature profile presented in Figure 4.2 and Figure 4.3, the aluminum

and zinc sprayed roughened PTFE, respectively.

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4.4.2 Heat Gun: Surfaces of PTFE/Teflon®

As previous stated in Section 4.4.1, the heating tests performed for the furnace heated

samples will be conducted using the described heat gun. The following tests will begin

with the PTFE samples, then HDPE, and will conclude with a summarization of results of

both heating methods. Finally, overall test conclusions will be made on the effects of

isolated heating, and heating aided with an air jet onto the specified polymer substrates.

Figure 4.10: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin PTFE, and Gun

Heated Smooth PTFE

59

In the figure above, a smooth unheated virgin PTFE specimen has been examined for

skiving marks that will aid in the observation of topographical changes after heating. The

Ra value of the surface was approximately 0.14 ± 0.01 µm, therefore smooth with very

faint features that can be seen in the 400x magnified images. Then, after performing the

heat test at 5 intervals of 80-90 °C, the previously faint skiving marks became more

defined. However, heating the substrate successfully defined deep markings, but the

remainder of the surface discrepancies remained the same in comparison to the unheated

virgin sample. This observation is further supported, as the average roughness of the

heated area was roughly 0.19 ± 0.02 µm. Thus, regardless of the heating aided with an

air-jet, the PTFE smooth substrate experiences negligible effects on the surface

topography. Additionally, the results of both heating tests; furnace heating, and the heat

gun, provided enough evidence that the smooth PTFE surface does not experience

significant change to the surface topography.

60

Figure 4.11: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin PTFE, Sandblasted Rough PTFE, and Gun Heated Rough PTFE

61

SEM images of smooth ‘virgin’ PTFE substrates were taken, then the samples were

mechanically treated until an average roughness of 1.55 ± 0.07 µm was achieved. As

expected, rippling occurred throughout the surface where valleys and peaks can be seen

in the ‘sand-blasted’ SEM images. Finally, after heating the substrate, the final SEM

images were captured, and the roughness analyzed. No conclusions could be made after

observation of the ‘heated + sb’ SEM images, this is consistent with the other furnace and

heat gun tested PTFE samples. The determined Ra value for the heated surface was

roughly 1.45 ± 0.11 µm, this test had the largest deviation of all heated PTFE samples.

Additionally, the overall roughness decreased by 0.10 µm, however, with a slight increase

in the surface deviation of 0.04 µm. The furnace heated samples experienced a drop of

only 0.04 µm from the unheated and heated samples, however with the introduction of an

air-jet increased that difference by 0.06 µm. This suggests that the substrate is beginning

to exhibit slight plastic behavior the closer the overall temperature gets to the materials

glass transition temperature.

4.4.3 Heat Gun: Surfaces of HDPE

Two HDPE samples were examined before and after the heat gun experiment under the

SEM. In the furnace test previously discussed, the existence of softening patterns was

observed correlating to the substrate temperature rise. Now, with the introduction of the

air-jet and thermal cycling, which more accurately represents the electric wire-arc, the

emphasis will be on examining any enhancement to this softening phenomenon.

62

Figure 4.12: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin HDPE, and Gun

Heated Smooth HDPE

First, the examination of an extremely smooth HDPE virgin sample was conducted and

in Figure 4.12 above, virtually no skiving marks can be identified. However, instead of the

typical skiving marks that are present in almost all virgin smooth polymer samples, there

ripples that can be seen at 200x and 400x magnification. Additionally, the surface

roughness after SEM examination of the surface was identified as approximately 0.15 ±

0.02 µm. Notice, that this Ra value is almost identical to the value determined for the

smooth PTFE sample in Figure 4.10, where virtually no surface features were observed.

Now, after subjecting the smooth virgin polymer to the heat gun procedure, the gun

heated smooth HDPE SEM- images were acquired. Immediately, distinct differences are

examined on the substrate surface where previously no prominent feature could be

examined. Clearly defined skiving marks oriented parallel to one another are visible

63

throughout the substrate surface. These emerging features clearly indicate softening of

the heating zone, where the temperature creates a viscous surface that the air-jet

modifies. However, the average roughness of the substrate after heating was

approximately 0.21 ± 0.03 µm, slightly higher than the unheated counterpart. The

appearance of these skiving features on the sample upon heating may contribute to this

minor change in surface roughness. Nevertheless, the observations of the furnace heated

HDPE suggested evidence that softening, and material flow was occurring on the

substrate surface. Now, with the addition of focused jet impingement, distinct differences

are recognized with developing skiving features. This emerging pattern suggests possible

material flow aided by the air-jet, along with supporting the softening concept described

previously. Finally, examination of the effect of the heat gun on the roughened HDPE

samples will resolve any concerns surrounding the discrepancies in these predictions.

64

Figure 4.13: 200x and 400x Magnification SEM Images of the Surfaces of Smooth Virgin HDPE, Sandblasted

Rough HDPE, and Gun Heated Rough HDPE

65

Finally, the last heat gun experiment will start by examining the smooth virgin PTFE

surface prior to any heating. In the figure above, in the virgin row, the presence of many

deep and faint skiving marks can be identified throughout the substrate surface. Following

the trends previously described, the presences of these markings will slightly increase the

overall surface roughness but will not attribute to any influence on the analysis of the gun

heated rough HDPE sample. Nevertheless, the virgin smooth surface of the HDPE

sample was approximately 0.16 ± 0.02 µm. Then, the substrate was sand blasted until a

uniform surface roughness of 1.59 ± 0.09 µm was achieved. In the ‘sand blasted’ row of

the figure, the common rippling pattern is observed on the surface that represent peaks

and valleys generated through the mechanical surface treatment. These observable

surface features will be the primary focus, that will provide indication for softening and top

surface material flow. The heat gun experiment on the smooth virgin HDPE suggested

that the skiving patterns created by the manufacturer, that represent a ‘slippery’ surface

will appear after the heating experiment. Therefore, attention to any presence of skiving

patterns will be taken after completing the 5-interval heat test at 90 °C. Finally, after

heating the substrate, SEM imaging of the substrate surface were taken and presented

in the ‘Heated’ row of the figure. Ripples are observed throughout the substrate surface,

as expected from the roughened sample, however as anticipated, skiving marks have

begun to emerge across the heating zone of the sample. In the figure above, you can see

in the ‘Heated’ row, skiving marks like that of the smooth virgin sample prior to any

mechanical treatment or heating. Additionally, the presence of these features suggest

that the surface roughness has drastically reduced, which can be verified with the

examined Ra value of approximately 0.34 ± 0.08 µm. Thus, upon heating the sample in

a procedure mimicking an electric wire-arc spray test, the roughened HDPE surface

experiences approximately 79% reduction in overall surface roughness. Additionally, this

provides evidence that softening of the substrate surface does exist for rough HDPE

surfaces when spraying aluminum via electric wire arc.

66

4.4.4 Heat Gun: Results and Discussion

The following figure is collection of the roughness data of the furnace heating and heat

gun tests examined throughout Chapter 4. Additionally, as the virgin and sand blasted

samples differ depending on the test, all presented values for those sets derive solely

from the heat gun procedure. Finally, the roughness data associated with the figure can

be found in the Appendix C.

Figure 4.14: Evaluated Ra values of specified polymers (0 – smooth, 20 – rough) at the virgin, sand blasted,

furnace heated, and post-heat gun states.

In Figure 4.14, like Figure 4.8, the polymers are organized starting with the roughened

PTFE (#20) substrate, followed with its smooth virgin counterpart (#0). Then, the HDPE

samples were illustrated in similar fashion, starting with roughened and ending with

smooth. Additionally, the black bars represent the virgin samples of the heat gun test,

prior to any heating or mechanical treatment. The orange bars represent the average

roughness of the surface after mechanically treating the substrates, these bars are only

present for samples indicated with the grit size of 20. Finally, the two heating bars are

represented as red for furnace heating examined in Section 4.3.3, and the blue bar

representing the heat gun results in the most recent analysis. Any error bars in the

experiment are associated with the standard roughness deviation evaluated for a sample

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set of 3 polymers per test. Summarizing points made in the furnace heating section, along

with the ones created for the heat gun during its analysis, the conclusions are:

1. Negligible differences in the surface topography and roughness were

observed for all PTFE samples, regardless of surface preparation and

heating method.

2. Smooth HDPE experiences no change in surface roughness or topography

when furnace heated, however small increases in Ra are examined after

Heat gun testing, along with emerging skiving features.

3. Roughened HDPE experiences an 18% reduction in surface roughness

with furnace heating, and an almost 79% decrease when introducing an

air-jet

These concluding points help emphasis the existence of surface modification on HDPE

during thermal spraying. The HDPE substrate experiences softening during deposition,

which results in higher possibilities of coating delamination. This occurs because the

temperature of depositing aluminum droplets onto the HDPE softens the outer layer,

preventing any mechanical interlocking at the interface. The possibility of manipulating

this substrate temperature will be evaluated, as heating the samples close to their

respective softening/glass-transition temperatures may affect adhesion at the metal-to-

polymer interface.

4.5 Heated Substrate Characterization

Now that the temperature effects on the topography of the polymer have been

established, this section will focus on the manipulating the temperature of the substrates

during the spraying procedure. Specifically, the average temperature of the polymers will

be raised to specific temperature zones. These zones are, the glass-transition

temperature of PTFE, and a high operation temperature where softening occurs for

HDPE. In Chapter 3, it was discovered that interfacial hooking aided in higher adhesion

between aluminum and PTFE. Examination of the effects of manipulating substrate

temperature on adhesion strength and interlocking properties will be the primary focus

that builds on the temperature and air-jet influences constructed in the previous section.

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Additionally, the differences between coating metal onto room temperature and heated

substrates will be established with examination of the interface through SEM-imaging.

4.5.1 Aluminum onto Heated PTFE and HDPE

In this section, only the heated rough PTFE temperature profile will be examined, as all

HDPE samples at elevated temperatures delaminated prior to establishing an aluminum

coating. Additionally, it should be assumed that all PTFE samples experience a relatively

similar profile, regardless of surface roughness, while spraying aluminum. Furthermore,

the number of achievable coatings has increased from the room temperature tests

performed in Chapter 3, which arises due to a slight change in the surface preparation.

Specifically, iso-propyl alcohol was left on the substrate longer which allowed it to

evaporate naturally resulting in a higher coating thickness. In contrast, the room

temperature samples were sprayed with pressurized air to remove any excess iso-propyl

on the surface. However, examination of the adhesion strength of the first bonding layer

will be conducted at the point of delamination mimicking the conditions of the room

temperature tests. Finally, the variable transformer used to power the heater cartridges

were adjusted to 70 Volts, in order to establish a substrate temperature of 100 °C, only

about 15°C below the glass transition temperature of PTFE (it ranges from 115°C to

125°C, see Table 2.1).

Figure 4.15: Temperature verse time graph of aluminum depositing onto a roughened PTFE substrate heated to roughly 100 °C, via heat cartridges and a variable transformer

69

In Figure 4.15 above, the rough substrate (Ra ~ 1.58 µm) was heated and stabilized at

an elevated temperature of roughly 96 °C. This temperature was achieved by setting up

the Powerstat® variable transformer [35] to regulate the voltage at 70 – 75 Volts,

increasing the substrate temperature gradually until the desired temperature was

achieved. Then, the electric wire-arc procedure for aluminum was conducted to achieve

a thick metal coating prior to the delamination conditions.

First, a sudden drop in temperature from 96 °C to roughly 90 °C was observed, and as

previously stated, this is caused by the air-jet hitting the substrate surface prior to the

molten aluminum droplets. However, as PTFE has a thermal conductivity of 0.25 W/m·K,

much lower than that of the thermocouple 1 mm bead, this sudden 6-degree temperature

drop does not signify a significant drop in the substrate temperature. Thus, ignoring the

sudden dip in temperature at the start of the first pass, the temperature of the substrate

rapidly increases to roughly 127 °C, slightly above the glass transition temperature of

PTFE (see Table 2.1). Then, after a 2-minute cooling period, the temperature rapidly

drops to approximately 98 °C, closer to the desire substrate temperature. However, the

maximum temperature after the second pass drastically decreases to roughly 115 °C,

which better represents the substrate temperature as we observe it gradually increase to

126 °C at the final pass. Therefore, the first pass did not appropriately indicate the

substrate temperature, but the second pass will be considered a more accurate

measurement. Nevertheless, we observe patterns that are comparable to the aluminum

deposition onto room temperature PTFE in Figure 4.2 and Figure 4.3. Specifically, that

the temperature of the substrate after the cooling phase gradually increases from roughly

96 °C to 104 °C at the last pass. This occurs due to the low thermal conductivity of the

substrate, as the sample is heated and cooled, progressively higher residual thermal

energy is maintained within the polymer. Additionally, we see the same increase in the

peak temperature after each pass of the wire-arc like depositing zinc onto HDPE at room

temperature. Finally, as the substrate’s base temperature remained within the specified

condition, and an approximately 425 ± 10 µm aluminum coating was achieved.

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4.5.2 Zinc onto Heated PTFE and HDPE

A zinc coating of 10 passes was achieved on both PTFE and HDPE substrates,

regardless of surface roughness, and just prior to any signs of delamination. The following

are the temperature measurements of the heated substrates, and the effects of molten

zinc on the surface temperature.

Figure 4.16: Temperature verse time graph of zinc depositing onto a roughened PTFE substrate heated to

roughly 106 °C, via heat cartridges and a variable transformer

In the figure above, zinc was deposited roughened PTFE surface (Ra ~ 1.59 µm) initially

at 106 °C which immediately experienced a temperature drop of roughly 16 °C. The

substrate experiences a decrease in overall substrate temperature because of impinging

air. Once the spray moves away the substrate heats up again and after approximately 1

minute the temperature of the substrate increases from 89 °C to roughly 103 °C.

Furthermore, the temperature of the substrate progressively drops until a minimum

temperature of roughly 84 °C is recorded as the substrate temperature. Similar patterns

are examined for the minimum spray peak, as the first pass resulted in an 89 °C substrate,

the final pass decreased the temperature to exactly 80 °C. The most important

observation is that, as we increase the number of passes the overall temperature

difference form the heated substrate to the valleys during spraying are gradually

71

decreasing. The 16-degree difference after the first pass, gradually decreased to an

almost 4 °C difference between the spraying condition and after the ‘heating’ phase.

In conclusion, the high temperature PTFE substrate experiences a cooling effect when

zinc is being deposited onto it. Additionally, this phenomenon did not prevent the zinc

from adhering to the surface, which achieved a thick coating. The average coating

thickness of the zinc onto the roughened and smooth PTFE substrates is approximately

370 ± 10 µm.

Figure 4.17: Temperature verse time graph of zinc depositing onto a roughened HDPE substrate heated to

roughly 55 °C, via heat cartridges and a variable transformer

In contrast to the zinc deposition on the heated PTFE substrate in Figure 4.16, the

roughened HDPE substrate does not experience cooling. Rather, the substrate

experiences a stabilized heating pattern with a reduction in cooling rate. First, the HDPE

substrate’s temperature is increased by the heating plate with a variable transformer set

to 55 volts. The plate raises the temperature of the samples to roughly 55 °C, a

temperature where softening of the polymer occurs, and the spray test begins with the

first coating only increases the temperature of the substrate by half a degree to 55.5 °C.

This pattern is like the zinc deposition onto heated PTFE, as the first pass does not

accurate depict the substrate temperature, however in the second pass a sudden

increase is observed to almost 57 °C. The temperature of the substrate peaks at the 5th

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pass at roughly 60 °C during spraying, however after the 1-minute cooling phase, the

temperature drops to 50.6 °C. This decrease in substrate temperature is consistent

throughout all heated substrates, as the number of passes increase, the substrate

temperature after cooling decreases which indicates a reduction in the magnitude of

thermal energy contained within the system. However, as the passes increase beyond

the 5th, the temperature of the substrate slightly decreases during zinc deposition.

In conclusion, the zinc deposited onto the HDPE substrate surface increases the overall

substrate temperature by roughly 5 °C at the 5th pass. Then, the substrate experiences a

loss of residual thermal energy resulting in a minor decrease of 2.5 °C from the maximum

peak achieved at the final coating. However, a thick coating was achieved on the smooth

and roughened HDPE surface of approximately 380 ± 10 µm.

4.5.3 SEM-Imaging of Coating-Substrate Interface

Specimens from all 8 tests described in Table 3.1 were performed with the heated

polymer substrates for 10 passes of the electric wire-arc with both metals. The average

calculated thickness of the aluminum and zinc coatings, as previously described, are…

• 425 ± 10 µm for… PTFE (Smooth and Roughened)

• 370 ± 10 µm for… PTFE (Smooth and Roughened)

• 380 ± 10 µm for… HDPE (Smooth and Roughened)

The SEM-imaging of aluminum onto heated rough PTFE and zinc onto heated rough

PTFE will be examined thoroughly, as these samples experienced the most significant

difference in adhesion strength in the testing performed in Chapter 3. However, a brief

examination of all successful tests will be provided after evaluating the roughened PTFE

samples.

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Figure 4.18: x250 Magnification Overview (OV1-2) SEM images of Aluminum onto Heated PTFE (20), Along

with x1.5k Magnified Images (A,C, and D) and x800 Magnification for (B) of Specified Interlocking

Mechanisms.

74

The interface between aluminum and the rough heated PTFE was examined in Figure

4.18 (OV1 and OV2) at x250 magnification. The SEM images presented were separated

into two sections, the image to the left represents the typical pattern observed throughout

the cross-section. The image on the right was selected, as it illustrates an uncommon

region in the interface where the intensity of ‘hooking’ is low, but still present.

Starting with the image to the left, it is apparent that the substrate-to-metal interface

experiences a high degree of mechanical interlocking. There are several locations in this

selected zone, that experiences a very deep hooking phenomenon. This deep hooking

was present in the room temperature samples, but at a lower degree as observed in

Section 3.4.2. However, this degree at which mechanical interlocking occurs on a room

temperature versus a heated substrate will be evaluated when examining the adhesion

strength associated with the heated sample. Now, the cross-sectional image to the right

inspects a low mechanical interlocking area that is relatively uncommon throughout the

examined sample. Although, this sample differs from the rigid curling patterns examined

in the previous image, deep interlocking can be observed throughout the length of the

interface. A deeper examination of these interlocking zones is illustrated in Figure 4.18,

images (A) to (D).

Starting with Figure 4.18 (A), the polymer and metal overlap and become tangled similar

to interlocking that was examined previously in Figure 4.6 (C). This ring-like interlocking

mechanism occurs instantaneously during deposition, as the molten metal droplets

redistribute the softened polymer substrate. Then, as a single branch of the molten metal

plunges deep within the specimen and intersects with another branch of a different or the

sample droplet, they combine to make the ring-like interlock. This pattern can also be

observed on image (B), where almost 5 branches are penetrating deep within the

polymer. Starting from the left of image (B), the first two branches have begun to create

a ring-like structure, and the two branches following them appear to have solidified just

prior to intersecting. Finally, a large aluminum fragment appears to be separated from the

coating itself, however if further polishing was performed on the cold-mounted specimen,

a connection would be found between the large fragment and the coating. Thus, these

zones indicate areas which the adhesion strength of the coating a significantly higher than

that of smoother samples. Analysis of images (C) and (D) do not provide any evidence of

75

‘deep’ hooking, or ring-like structures, however aluminum branches can still be observed

throughout the interface. These interlocking locations will aid overall adhesion strength,

but not to the extent observed in images (A) and (B).

Figure 4.19: x250 Magnification Overview (OV1-2) SEM images of Zinc onto Heated PTFE (20), Along with x1.5k Magnified Images (A-D) of Specified Interlocking Mechanisms.

76

Finally, in Figure 4.19 above, zinc deposited onto roughened PTFE specimens initially

heated close to glass transition were cold mounted and polished for SEM imaging. The

images revealed ring-like hooking and deep branching mechanisms that has been

observed in the mechanically treated samples. Two overview (OV1 & 2) images were

captured of the zinc-to-PTFE interface, where several instances of zinc branches

penetrating the polymer substrate can be observed. Specifically, 4 sections of the

overviews (A-D) were considered the most representative in characterizing the adhesion

of zinc onto the heated substrate.

In Figure 4.19 (A), a ring-like structure that has been common in the aluminum coated

PTFE samples has developed on the zinc coated polymer. This structure was created as

the substrate was heated to a softened point, allowing the zinc splats to propagate beyond

the polymer surface. At room temperature, zinc has not proved to establish deep

mechanical bonding with either HDPE or PTFE, as observed in Figure 3.7. However,

along with interlocking observed in image(A), in OV2, to the right of image (D), another

ring-like interlock is observed. Thus, examination of the interface suggests that adhesion

strength between the zinc and the polymer should increase with the observation of these

strong bonding mechanisms. Similarly, in Figure 4.19 (B to D) it is observed that clearly

defined mechanical interlocking has been established throughout the interface, in contrast

to the room temperature samples previously examined. The zinc coatings on room

temperature PTFE, demonstrated very little mechanical interlocking, and observations of

the coating interface provided little evidence of branching that may strengthen the coating

adhesion. Thus, examination of the pull-test results on the zinc coated heat samples will

provide clear evidence of the improvements in adhesion influenced by substrate

temperature.

4.5.4 Adhesion Results and Discussion

The following figure presents the adhesion strengths of tests 1-8 described in Section

3.5.1 and the new results evaluated for the heated substrates. All room temperature

adhesion strengths were collected from Figure 3.8, and the data along with the standard

deviations indicated by the grey brackets can be found tabulated in the appendices.

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Figure 4.20: Adhesion Strength Values for Room Temperature and Heated Polymers coated with Zinc and

Aluminum, at varying surface roughness averages.

Finally, all the adhesion tests for the room temperature and heated substrates were

performed and tabulated into the figure above. For simplicity, it should be assumed that

the average roughness values for the smooth samples are close to 0.20 µm and the rough

samples are roughly 1.60 µm. However, all roughness data and standard deviations

associated with the results above will be provided in the appendices.

Now, beginning with the blue bar and green bars representing zinc coatings onto room

temperature, and heated substrates, respectively. As previously stated, the adhesion

strength of zinc coatings onto PTFE increase from approximately 0.43 MPa and 0.85

MPa, for room temperature smooth and rough, respectively. Now, when the PTFE

substrates are heated the adhesion strength for the smooth and roughened polymers

increase to 0.75 MPa and 1.42 MPa, respectively. Thus, as the substrates are heated the

smooth surface experiences a 74% increase in adhesion, and the roughened surface

approximately 67%. The drastic increase in adhesion for the smooth surface is

contributed by the increased mechanical interlocking that occurs when the substrate is

held in a softened state. This allows the molten metal time to penetrate the substrate

further than it would on the room temperature specimen before solidifying. Additionally,

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this penetration affect occurs for the roughened counterpart, however at a lower

percentage increase because the surface morphology already contributes to deeper

interlocking for the room temperature substrate. The observation made for the zinc onto

heated PTFE substrate is consistent when applied to the heated HDPE specimens. The

HDPE samples have adhesion strengths of 0.49 MPa to 0.72 MPa, for smooth and rough

substrates at room temperature, respectively. Additionally, an increase in adhesion

strength is experienced when elevating the HDPE samples to a softening temperature.

Pull tests performed onto the heated HDPE substrates resulted in 0.70 MPa for the

smooth substrate, and 1.07 MPa for the roughened sample. This resulted in a 43% and

almost 49% increase in adhesion strength for the smooth and roughened samples,

respectively.

The orange and red bars represent aluminum deposited onto room temperature, and

heated substrates, respectively. The first observation that should be noted is that

aluminum was not able to adhere to HDPE regardless of the surface preparation and

substrate temperature. This result was expected, as the substrate is more likely to

experience softening and melting when at elevated temperature close to its melting point.

Now, introducing mechanical treatment onto the smooth PTFE substrate resulted in an

increase in adhesion strength from 0.76 MPa to 1.37 MPa. This increase was predicted

after examining the SEM images of the interface, where deep interlocking occurs

regardless of surface preparation, however the roughened samples experienced this

phenomenon at higher intensities. Furthermore, as the substrates were heated close to

the glass transition temperature, the overall adhesion strengths increased significantly.

The smooth PTFE evaluated at 0.76 MPa at room temperature, experienced an adhesion

strength of 1.64 MPa, about a 116% increase when heated. Additionally, the roughened

PTFE sample evaluated at 1.37 MPa, was determined to have an adhesion strength of

2.45 MPa on the heated substrates, an approximately 79% increase. As examined in the

zinc coatings on the heated PTFE substrates, these patterns in the increased adhesion

strength are consistent regardless of the deposited metal. The smooth substrate

experiences a higher difference because the room temperature samples do not allow the

metal to penetrate deep within the polymer as the softening phase are too short to permit

material flow. However, at elevated temperatures close to glass transition, the

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polymerization process that restores the rigidity of the sample is slowed which allows time

for the metal to mix with the polymer creating ring-like structures examined in the SEM

images in Section 4.5.3. All results evaluated in this section are tabulated in the table

below.

Table 4.1: Adhesion strengths of tests (1-8) for room temperature (RT) and heated substrates (HT). Samples

that could not achieve coatings are indicated with (-). All adhesion strength values are in MPa.

Substrates PTFE/Teflon® HDPE

Smooth Rough Smooth Rough

RT: Zn 0.43 0.85 0.49 0.72

HT: Zn 0.75 1.42 0.70 1.07

RT: Al 0.76 1.37 - -

HT: Al 1.64 2.45 - -

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Conclusions

5.1 Summary and Final Remarks

This study investigated the characteristics surrounding the thermal spray metallization of

aluminum onto various polymers. Specifically, an electric wire-arc was used to coat 99.5%

aluminum and 99.9% zinc wires onto polytetrafluoroethylene/Teflon® (PTFE) and ultra-

high molecular weight polyethylene (UHMWPE/ HDPE). These polymers were examined

at two different surface criteria; a smooth surface provided by the manufacturer, and a

roughened surface acquired through mechanical treatment.

Specifically, a mechanical treatment methodology was created for sandblasting, which

would result in uniform surface roughness averages (Ra) without damaging the polymer.

This resulted in polymers categorized as smooth (or ‘0’) to have an Ra value of

approximately 0.20 µm, and roughened (or ‘20’) samples achieving an Ra value of roughly

1.60 µm. Then, the smooth and roughened polymers were coated with aluminum and zinc

until the samples would delaminate, defining the adhesion limits. Once, the limits were

established, and thick metallic coatings were acquired, pull-tests were performed to

determine the adhesion strengths of the metal-to-polymer interface. Finally, the following

results were determined from thermal spraying and adhesion tests…

1. A thick aluminum coating of 260 – 400 µm was obtained on a smooth PTFE

substrate.

2. All polymer substrates were able to achieve a thick zinc coating of 260 –

400 µm, regardless of surface roughness

3. No aluminum coatings were achieved for HDPE, regardless of surface

preparation

4. Increasing the surface roughness of the polymer substrates resulted

significant increase in the adhesion strength of the coating.

Scanning electron microscopic (SEM) examination of the metal-to-polymer interface of

the aluminum to PTFE polymers showed that substrate temperature may influence

delamination during thermal spraying. An apparatus was built to heat the substrate during

81

aluminum and zinc deposition. Additionally, temperature profiles were taken to examine

the thermal cycling experienced by the specimens during thermal spraying.

Two heating tests were carried out to evaluate the influence of temperature on the

substrate. The first test isolated the samples in a furnace where the substrates would be

heated undisturbed. This resulted in surfaces that are only influenced by the increase in

temperature, however the second test examined the influence of temperature and air-jet

impingement. A heat gun was used to simulate the thermal cycling, and maximum

temperatures of the thermal spray test. Evaluating the change in surface topography and

roughness of these two tests will determine the effects of the spray gun onto PTFE and

HDPE. After tabulating and analyzing the results of the tests, it was determined that…

1. All PTFE samples experienced very little change in surface topography and

roughness, after heating the substrate with and without an air-jet

2. When heating the HDPE substrates, without an air-jet, the smooth

specimens experience no change, but the Ra of the roughened specimens

decreased by 18%.

3. Heating smooth HDPE samples, with an air-jet, result in negligible change

in the surface roughness. However, skiving patterns emerge throughout

the surface, suggesting softening and re-arrangement of the material.

4. Heating rough HDPE samples with an air-jet result in a drastic decrease in

the Ra by almost 80%. Additionally, skiving patterns indicating smooth

zones emerge, suggesting complete softening of the roughened areas.

A heating plate and top cover were constructed to elevate the temperature of the

substrate during spraying. The smooth and rough PTFE samples were heated to roughly

100 °C, close to the glass transition temperature range of 115-125 °C. Additionally, the

smooth and rough HDPE samples were heated to a temperature of 55 °C, a temperature

where softening of the polymer occurs. Then, aluminum and zinc were coated onto the

samples, and adhesion tests and SEM-imaging were performed to determine the

differences between the heated and room temperature substrates. The following results

were determined from the pull-tests and image analysis:

82

1. Zinc coated smooth and rough PTFE, experienced 74% and 67% increase

in adhesion strength, respectively, when heated close to the glass transition

2. Zinc coated smooth and rough HDPE, experienced 43% and 49% increase

in adhesion strength, respectively, when heated to a softening temperature

3. Aluminum coated smooth and rough PTFE, experienced 116% and 79% in

adhesion strength, respectively, when heated close to glass transition

4. HDPE was not able to achieve aluminum coatings at room, and elevated

temperatures regardless of surface preparation.

Thus, adhesion of a thick aluminum coating was achieved onto a smooth PTFE surface,

and the adhesion strength was enhanced with mechanical treatment via sandblasting.

Additionally, extensive testing provided evidence that manipulation of the substrate

temperature will result in strong adhesion between the metal and polymer. Increasing

substrate temperature results in enhanced mechanical interlocking resulting from material

flow when in a plastic state. However, when depositing aluminum onto HDPE, a polymer

with a low melting temperature, delamination will result as consequence of high

temperature metal spraying.

83

5.2 Future Work

Based on the conclusions of this experimental study of metal-to-polymer adhesion, the

following recommendations for future work focus on three primary aspects; product

testing, substrate manipulation, and procedural changes.

For Product Testing:

❖ Aluminum coated PTFE either initially at room temperature or elevated close to

glass transition, should be tested for thermal and electrical conductivity.

❖ The coated polymers efficiency in thermal and electrical conductivity should be

compared with commercially available products.

❖ Evaluation of the influence of thermal stresses on delamination for the metal

coated polymers should be conducted.

❖ Characterization of the coated polymer’s tensile and sheer strengths should be

conducted, in order to establish specimens viable for industrial and commercial

use.

For Substrate Manipulation:

❖ Substrate cooling during the thermal spray procedure should be considered, to

further support the temperature influence on metal-to-polymer adhesion. A

possible test of HDPE cooled to -20 °C prior aluminum deposition would produce

interesting results further developing the theories examined in this report.

For Procedural Changes:

❖ The influence of thermal spray variables on polymer adhesion should be

examined. Variables such as; spraying distance, voltage, current, and air-jet flow

were constants in this report, however, as mentioned in Chapter 1, Chen et al. [44]

achieved thick zinc coatings onto 3D printed polymers at an 4 inch spray distance.

84

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89

Appendix A

SEM Imaging: Porosity of Aluminum and Zinc Coatings

The following images were used for testing the porosity of the aluminum and zinc

coatings, which were processed through the ImageJ software.

90

The following table is the porosity percentages associated with the SEM-imaging above,

all values were calculated through ImageJ. First, the images were measured, and a scale

was selected. Then, the image was transformed into 8-bit jpeg, and an appropriate

threshold was selected that captured all visible pores. The images were then divided into

4 sections, and porosity was measured.

Sample Coating Porosity (%) Average

Porosity (%)

Porosity Standard Deviation

(%)

1 Al

7.77

10.0 2.47

12.9

11.8

9.01

2 Al

8.10

14.5

7.99

8.10

3 Zn

4.33

4.83 1.17

5.62

4.59

4.02

4 Zn

3.44

4.15

7.47

4.98

91

Appendix B

Temperature Measurements: Room Temperature Substrates

For the following temperature information only specified portions of the temperature

measurements will be illustrated in the figures and tables below. Typical temperature tests

will last for 30 minutes to an hour, which results in 1000-3000 data points collected during

deposition. Including the temperature data from the 4 individual thermocouples, this

results in a minimum of 4000 temperature measurements per test. Thus, all temperatures

represented below are the averages determined from the 4-thermocouple set-up

described in chapter 2. Additionally, the tabulated temperature data will only represent 1-

2 passes of the electric-wire arc for the specific test.

Zinc onto PTFE

The following tabulated temperature measurements represent the 1st and 2nd pass of

the wire-arc depositing zinc onto a roughened PTFE sample.

92

Time (s)

Temp (°C)

107.7 24.1 129.9 30.0 152.1 27.4 174.3 32.3

108.8 24.1 131.0 29.7 153.2 27.3 175.4 32.1

109.9 24.1 132.1 29.5 154.3 29.1 176.5 31.8

111.0 25.5 133.2 29.3 155.4 28.8 177.6 31.7

112.1 25.4 134.3 29.1 156.5 33.4 178.7 31.4

113.2 29.1 135.4 29.0 157.6 32.9 179.8 31.2

114.3 28.0 136.5 28.8 158.7 38.2 180.9 31.0

115.4 33.0 137.6 28.6 159.8 35.4 182.0 30.8

116.6 30.9 138.8 28.5 161.0 38.3 183.2 30.7

117.7 35.9 139.9 28.4 162.1 37.4 184.3 30.5

118.8 34.7 141.0 28.3 163.2 37.8 185.4 30.3

119.9 34.7 142.1 28.1 164.3 36.3 186.5 30.2

121.0 33.7 143.2 28.0 165.4 35.5 187.6 30.1

122.1 33.3 144.3 27.9 166.5 35.1

123.2 32.4 145.4 27.8 167.6 34.5

124.3 31.8 146.5 27.8 168.7 34.0

125.4 31.4 147.6 27.6 169.8 33.6

126.5 30.9 148.7 27.4 170.9 33.3

127.7 30.7 149.9 27.5 172.1 33.0

128.8 30.3 151.0 27.5 173.2 32.6

Zinc onto HDPE

The following table illustrates the 1st and 2nd pass of the electric wire-arc depositing zinc

onto a initially room temperature roughened HDPE substrate.

93

Time (s)

Temp (°C)

67.7 23.9 89.9 30.6 112.1 31.1 134.3 33.5

68.8 24.0 91.0 30.4 113.2 30.6 135.4 33.2

69.9 24.1 92.1 30.3 114.3 35.5 136.5 33.0

71.0 24.6 93.2 30.1 115.4 35.3 137.6 32.9

72.2 25.2 94.4 29.8 116.6 39.6 138.8 32.8

73.3 25.7 95.5 29.8 117.7 38.5 139.9 32.5

74.4 26.9 96.6 29.7 118.8 39.3 141.0 32.4

75.5 28.3 97.7 29.5 119.9 38.5 142.1 32.3

76.6 33.6 98.8 29.4 121.0 37.7 143.2 32.1

77.7 31.8 99.9 29.2 122.1 36.9 144.3 32.1

78.8 33.7 101.0 29.3 123.2 36.3 145.4 31.8

79.9 33.1 102.1 29.0 124.3 36.0 146.5 31.7

81.0 33.7 103.2 29.0 125.4 35.7 147.6 31.5

82.1 32.8 104.3 28.9 126.5 35.4 148.7 31.4

83.3 32.8 105.5 28.8 127.7 35.0 149.9 31.3

84.4 32.2 106.6 28.8 128.8 34.7 151.0 31.2

85.5 31.7 107.7 28.9 129.9 34.3 152.1 31.1

86.6 31.3 108.8 28.8 131.0 34.1 153.2 31.3

87.7 31.0 109.9 29.4 132.1 33.9 154.3 31.5

88.8 30.8 111.0 29.4 133.2 33.7 155.4 32.5

Aluminum onto PTFE

The following table represents the first pass of the wire-arc depositing aluminum onto an

initially room temperature roughened PTFE substrate.

94

Time (s)

Temp (°C)

360.8 25.8 383.0 50.7 405.2 42.1 427.4 39.0

361.9 25.9 384.1 49.9 406.3 41.9 428.5 38.9

363.0 27.9 385.2 49.0 407.4 41.7 429.6 38.8

364.1 39.7 386.3 48.3 408.5 41.5 430.7 38.6

365.2 41.1 387.4 47.7 409.6 41.3 431.8 38.5

366.3 53.1 388.5 47.1 410.7 41.2 432.9 38.4

367.4 61.3 389.6 46.6 411.8 41.0 434.0 38.3

368.5 67.1 390.7 46.1 412.9 40.8 435.1 38.2

369.6 86.4 391.8 45.7 414.0 40.7 436.2 38.1

370.7 73.9 392.9 45.3 415.1 40.6 437.3 38.0

371.9 84.8 394.1 44.9 416.3 40.4 438.5 37.9

373.0 70.5 395.2 44.6 417.4 40.2 439.6 37.8

374.1 74.8 396.3 44.2 418.5 40.1 440.7 37.7

375.2 66.1 397.4 43.9 419.6 39.9 441.8 37.6

376.3 63.5 398.5 43.6 420.7 39.8 442.9 37.5

377.4 59.6 399.6 43.4 421.8 39.7 444.0 37.4

378.5 56.9 400.7 43.2 422.9 39.5 445.1 37.3

379.6 54.8 401.8 42.9 424.0 39.4 446.2 37.2

380.7 53.2 402.9 42.6 425.1 39.3 447.3 37.1

381.8 51.8 404.0 42.4 426.2 39.1 448.4 37.0

Temperature Measurements: Heated Substrates

Zinc onto Heated PTFE

The following table represents the 1st pass of zinc sprayed onto a roughened PTFE

sample initially heated close to its glass transition temperature.

95

Time (s)

Temp (°C)

427.4 105.8 449.6 95.1 471.8 101.0 494.0 101.8 516.2 102.4

428.5 105.8 450.7 91.3 472.9 101.0 495.1 101.8 517.3 102.4

429.6 105.7 451.8 94.3 474.0 100.9 496.2 101.9 518.4 102.4

430.7 105.7 452.9 89.2 475.1 101.0 497.3 101.9 519.5 102.5

431.8 105.7 454.0 94.0 476.2 101.1 498.4 102.0 520.6 102.5

432.9 105.7 455.1 96.2 477.3 101.3 499.5 102.0 521.7 102.5

434.0 104.4 456.2 97.3 478.4 101.4 500.6 101.9 522.8 102.6

435.1 104.5 457.3 98.0 479.5 101.6 501.7 102.0 523.9 102.0

436.2 101.4 458.4 98.6 480.6 101.7 502.8 102.1 525.0 101.6

437.3 102.3 459.5 99.1 481.7 101.6 503.9 102.3 526.1 100.0

438.5 98.2 460.7 99.4 482.9 101.6 505.1 102.3 527.3 100.4

439.6 99.8 461.8 99.6 484.0 101.6 506.2 102.5 528.4 96.7

440.7 96.1 462.9 99.8 485.1 101.6 507.3 102.4 529.5 98.5

441.8 97.1 464.0 100.1 486.2 101.6 508.4 102.4 530.6 94.6

442.9 95.5 465.1 100.1 487.3 101.7 509.5 102.4

444.0 95.7 466.2 100.4 488.4 101.8 510.6 102.3

445.1 96.0 467.3 100.6 489.5 101.9 511.7 102.4

446.2 94.0 468.4 100.6 490.6 101.9 512.8 102.3

447.3 95.9 469.5 100.7 491.7 101.7 513.9 102.4

448.4 92.9 470.6 100.9 492.8 101.7 515.0 102.4

Zinc onto Heated HDPE

The first two passes of zinc deposited onto a roughened HDPE20 were ignored and

focus was put on the 3rd pass in the figure above, for the tabulated results below.

96

Time (s)

Temp (°C)

1860.4 53.6 1882.6 54.7 1904.8 54.1 1927.0 53.2

1861.5 53.5 1883.7 55.0 1905.9 53.9 1928.1 53.2

1862.6 53.5 1884.8 55.0 1907.0 53.9 1929.2 53.1

1863.7 53.4 1885.9 55.0 1908.1 53.9 1930.3 53.1

1864.8 52.6 1887.0 54.9 1909.2 53.8 1931.4 53.1

1865.9 52.3 1888.1 54.9 1910.3 53.8 1932.5 53.1

1867.0 51.6 1889.2 54.8 1911.4 53.8 1933.6 53.1

1868.1 52.0 1890.3 54.7 1912.5 53.7 1934.7 53.0

1869.2 52.0 1891.4 54.7 1913.6 53.6 1935.8 53.0

1870.4 52.1 1892.6 54.6 1914.8 53.6 1937.0 53.0

1871.5 54.4 1893.7 54.5 1915.9 53.5 1938.1 53.0

1872.6 53.8 1894.8 54.5 1917.0 53.5 1939.2 53.0

1873.7 57.4 1895.9 54.5 1918.1 53.5 1940.3 53.0

1874.8 56.4 1897.0 54.4 1919.2 53.5 1941.4 52.9

1875.9 58.2 1898.1 54.4 1920.3 53.5 1942.5 52.8

1877.0 59.5 1899.2 54.3 1921.4 53.4 1943.6 52.8

1878.1 57.5 1900.3 54.3 1922.5 53.4 1944.7 52.8

1879.2 57.1 1901.4 54.2 1923.6 53.3 1945.8 52.7

1880.3 56.1 1902.5 54.2 1924.7 53.3 1946.9 51.7

1881.5 54.3 1903.7 54.1 1925.9 53.3 1948.1 51.7

Aluminum onto Heated PTFE

The following table illustrates the 1st pass of aluminum onto a roughened PTFE sample

heated close to its glass transition temperature

97

Time (s)

Temp (°C)

1080.0 95.6 1102.2 94.6 1124.4 115.1 1146.6 99.9 1168.8 98.3

1081.1 95.7 1103.3 93.4 1125.5 124.6 1147.7 99.7 1169.9 98.3

1082.3 95.7 1104.5 93.8 1126.7 119.4 1148.9 99.5 1171.1 98.3

1083.4 95.9 1105.6 94.5 1127.8 114.7 1150.0 99.5 1172.2 98.2

1084.5 95.9 1106.7 94.9 1128.9 111.0 1151.1 99.5 1173.3 98.1

1085.6 95.9 1107.8 95.2 1130.0 108.5 1152.2 99.3 1174.4 98.0

1086.7 95.9 1108.9 95.4 1131.1 106.8 1153.3 99.3 1175.5 98.0

1087.8 95.7 1110.0 95.6 1132.2 105.5 1154.4 99.3 1176.6 98.1

1088.9 95.7 1111.1 95.4 1133.3 104.5 1155.5 99.1 1177.7 98.0

1090.0 95.8 1112.2 94.6 1134.4 103.7 1156.6 99.0 1178.8 97.9

1091.1 95.7 1113.3 92.1 1135.5 103.2 1157.7 98.8 1179.9 97.8

1092.2 95.7 1114.4 92.3 1136.6 102.6 1158.8 98.6 1181.0 97.8

1093.4 95.8 1115.6 90.7 1137.8 102.0 1160.0 98.6 1182.2 97.8

1094.5 95.8 1116.7 89.9 1138.9 101.5 1161.1 98.7 1183.3 97.8

1095.6 95.8 1117.8 90.2 1140.0 101.1 1162.2 98.6 1184.4 97.9

1096.7 95.9 1118.9 95.4 1141.1 100.8 1163.3 98.5 1185.5 97.9

1097.8 95.9 1120.0 94.3 1142.2 100.7 1164.4 98.5 1186.6 97.7

1098.9 95.9 1121.1 117.6 1143.3 100.6 1165.5 98.5 1187.7 97.8

1100.0 95.9 1122.2 107.9 1144.4 100.3 1166.6 98.5 1188.8 97.7

1101.1 95.6 1123.3 127.3 1145.5 100.1 1167.7 98.3 1189.9 97.7

Temperature Measurements: Heat Gun

Substrate Heating for HDPE and PTFE

The following table will present the first heating cycle of the heat gun test.

98

Time (s)

Temp (°C)

14.4 23.4 36.6 76.7 58.8 60.4 81.0 57.3

15.5 23.4 37.7 78.8 59.9 60.1 82.1 57.1

16.7 23.4 38.9 80.7 61.1 59.9 83.3 57.0

17.8 23.4 40.0 82.5 62.2 59.7 84.4 56.9

18.9 23.4 41.1 84.4 63.3 59.6 85.5 56.7

20.0 23.4 42.2 84.0 64.4 59.4 86.6 56.6

21.1 24.4 43.3 80.2 65.5 59.2 87.7 56.5

22.2 29.5 44.4 74.7 66.6 59.1 88.8 56.3

23.3 35.2 45.5 70.6 67.7 58.9 89.9 56.2

24.4 40.5 46.6 68.0 68.8 58.8 91.0 56.1

25.5 45.3 47.7 66.3 69.9 58.6 92.1 56.0

26.6 49.6 48.8 65.0 71.0 58.5 93.2 55.9

27.8 53.6 50.0 64.1 72.2 58.4

28.9 57.2 51.1 63.3 73.3 58.2

30.0 60.6 52.2 62.6 74.4 58.1

31.1 63.8 53.3 62.1 75.5 58.0

32.2 66.8 54.4 61.7 76.6 57.8

33.3 69.5 55.5 61.2 77.7 57.7

34.4 72.2 56.6 60.9 78.8 57.5

35.5 74.6 57.7 60.7 79.9 57.4

Appendix C

All values for the following tables are Ra values in µm. Additionally, the variables in the

roughness charts are compressed for organization so terms can be found below:

• Mat = Material

• G# = Grit Size Number, 20 = Rough and 0 = Smooth

• L/M/R = Left/Middle/Right, the location a roughness measurement was taken

• Avg = average of the Ra values measured for the test set

• Dev = the standard deviation of the Avg

• Favg = final average value of all tests in a group of sets (3 samples, 27

measurements, average of all measurements)

• Fdev = standard deviation of the Favg

99

Roughness Data: Furnace Heating of PTFE & HDPE

Virgin Mechanically Treated Furnace Heated @ 90

Te

st

Ma

t

G#

L

M

R

avg

de

v

Fa

vg

Fd

ev

L

M

R

avg

de

v

Fa

vg

Fd

ev

L

M

R

avg

de

v

Fa

vg

Fd

ev

1

PT

FE

0

0.2

6

0.2

3

0.2

3

0.2

64

0.0

23

0.2

2

0.0

2

- - - - - - -

0.2

2

0.2

5

0.2

4

0.2

50

0.0

36

0.2

0

0.0

2

0.2

5

0.2

8

0.2

5

- - - - - - -

0.2

2

0.1

9

0.3

0.2

8

0.2

9

0.3

1

- - - - - - -

0.2

8

0.2

5

0.3

2

PT

FE

0

0.1

2

0.0

9

0.1

2

0.1

13

0.0

15

- - - - - - -

0.0

9

0.0

9

0.1

1

0.1

01

0.0

07

0.1

1

0.0

8

0.1

4

- - - - - - -

0.1

0.1

1

0.1

0.1

1

0.1

1

0.1

4

- - - - - - -

0.1

0.1

0.1

1

3

PT

FE

0

0.2

7

0.2

8

0.2

8

0.2

73

0.0

10

- - - - - - -

0.2

4

0.2

4

0.2

7

0.2

51

0.0

12

0.2

8

0.2

7

0.3

0

- - - - - - -

0.2

6

0.2

6

0.2

6

0.2

6

0.2

6

0.2

6

- - - - - - -

0.2

5

0.2

3

0.2

5

100

4

PT

FE

20

0.6

8

0.6

2

0.7

1

0.6

98

0.0

33

0.6

8

0.0

3

1.7

1

1.6

3

1.5

4

1.5

8

0.0

7

1.5

8

0.0

6

1.6

7

1.5

6

1.5

9

1.5

4

0.0

6

1.5

4

0.0

6

0.6

9

0.7

0.7

8

1.6

6

1.5

1

1.4

9

1.5

4

1.4

9

1.4

8

0.6

7

0.6

8

0.7

5

1.5

9

1.6

2

1.4

9

1.5

4

1.5

7

1.4

6

5

PT

FE

20

0.6

2

0.6

5

0.6

2

0.6

28

0.0

18

1.5

4

1.6

1.5

8

1.5

7

0.0

5

1.6

6

1.6

1

1.6

2

1.5

3

0.0

8

0.6

3

0.6

4

0.6

1.6

5

1.5

5

1.6

2

1.4

4

1.5

1.4

2

0.6

5

0.6

5

0.5

9

1.5

9

1.5

2

1.4

9

1.5

1.5

1.5

1

6

PT

FE

20

0.6

8

0.7

6

0.6

0.7

10

0.0

38

1.6

4

1.6

5

1.6

2

1.5

8

0.0

6

1.5

5

1.6

2

1.5

9

1.5

5

0.0

4

0.7

1

0.7

1

0.7

8

1.5

8

1.5

8

1.5

1

1.5

3

1.5

6

1.5

1

0.7

6

0.6

8

0.7

1

1.5

1.6

3

1.5

1

1.5

2

1.5

9

1.5

7

PE

0

0.1

7

0.1

6

0.2

1

0.1

63

0.0

13

0.1

6

0.0

1

- - - - - - -

0.1

7

0.1

7

0.1

6

0.1

57

0.0

15

0.1

5

0.0

1

0.1

6

0.1

7

0.1

6

- - - - - - -

0.1

3

0.1

5

0.1

4

0.1

6

0.1

5

0.1

3

- - - - - - -

0.1

8

0.1

6

0.1

5

8

PE

0

0.1

8

0.2

0.1

7

0.1

63

0.0

15

- - - - - - -

0.1

7

0.1

6

0.1

5

0.1

58

0.0

13

0.1

5

0.1

4

0.1

6

- - - - - - -

0.1

7

0.1

5

0.1

4

0.1

7

0.1

4

0.1

6

- - - - - - -

0.1

8

0.1

4

0.1

6

9

PE

0

0.1

7

0.1

6

0.1

5

0.1

60

0.0

07

- - - - - - -

0.1

6

0.1

4

0.1

5

0.1

43

0.0

12

0.1

8

0.1

6

0.1

6

- - - - - - -

0.1

5

0.1

5

0.1

2

0.1

6

0.1

6

0.1

4

- - - - - - -

0.1

3

0.1

5

0.1

4

101

10

PE

20

0.2

8

0.2

6

0.2

5

0.2

58

0.0

16

0.2

4

0.0

1

1.6

9

1.6

6

1.5

5

1.5

8

0.0

7

1.5

9

0.0

6

1.2

1.2

9

1.2

9

1.2

8

0.0

3

1.3

1

0.0

5

0.2

7

0.2

5

0.2

5

1.6

5

1.5

1.5

5

1.2

8

1.3

2

1.3

0.2

1

0.2

8

0.2

7

1.5

6

1.5

4

1.5

1.2

6

1.3

1

1.2

7

11

PE

20

0.2

8

0.2

9

0.2

8

0.2

91

0.0

12

1.6

5

1.5

8

1.6

2

1.6

0

0.0

4

1.3

3

1.3

2

1.4

6

1.3

50

0.0

48

0.3

1

0.3

0.2

9

1.6

1

1.6

1

1.5

8

1.3

5

1.3

6

1.3

8

0.2

6

0.3

1

0.3

1.5

4

1.6

7

1.5

4

1.3

6

1.2

8

1.3

1

12

PE

20

0.1

5

0.2

0.1

5

0.1

68

0.0

15

1.6

2

1.5

5

1.6

1

1.5

8

0.0

7

1.2

3

1.3

2

1.4

3

1.3

11

0.0

81

0.1

7

0.1

7

0.1

5

1.6

5

1.6

8

1.6

2

1.3

6

1.3

5

1.3

8

0.1

6

0.2

0.1

6

1.4

8

1.5

1

1.5

1.2

3

1.1

6

1.3

4

Roughness Data: Heat Gun test of PTFE & HDPE

The following table is the roughness data associated with the heat gun tests performed

in chapter 4 of this report.

102

Identification Raw Sample Sand Blasted Gun Heated Samples

Test Mat. G#

L M R Avg Dev L M R Avg Dev L M R Avg Dev

1 PTFE 20

0.28 0.30 0.31 0.30 0.02 1.53 1.55 1.58 1.55 0.07 1.36 1.51 1.47 1.45 0.11

2 PTFE 0

0.14 0.14 0.15 0.15 0.01 0.00 0.00 0.00 0.00 0.00 0.17 0.19 0.22 0.19 0.02

3 PE 20

0.15 0.16 0.16 0.16 0.02 1.48 1.64 1.64 1.59 0.09 0.30 0.34 0.51 0.38 0.19

4 PE 0 0.15 0.13 0.16 0.15 0.02 0.00 0.00 0.00 0.00 0.00 0.18 0.22 0.24 0.21 0.03

Combined Roughness Data for Heating Tests

103

Appendix D

Adhesion Pull Tests: Room Temperature Samples #

Ma

t

Gri

t #

Wi

Ti

Ra

(µ

m)

WF

TF

Co

at

Wd

ep

Tc

oa

tin

g

Ad

he

sio

n

Str

en

gth

(M

pa

)

Av

g A

dh

es

ion

(Mp

a)

Sta

nd

ard

De

v

(Mp

a)

1

PT

FE

0

18

.50

3.3

5

0.2

4

19

.50

3.6

4

Al

1.0

0

0.3

0

0.6

4

0.7

6

0.0

8

2

PT

FE

0

18

.40

3.3

2

0.1

8

19

.30

3.6

2

Al

0.9

0

0.3

0

0.7

3

3

PT

FE

0

17

.30

3.3

2

0.2

6

18

.30

3.6

2

Al

1.0

0

0.3

0

0.8

1

4

PT

FE

0

18

.20

3.3

7

0.2

9

19

.20

3.6

6

Al

1.0

0

0.2

9

0.7

5

5

PT

FE

0

18

.30

3.3

4

0.1

7

19

.20

3.6

1

Al

0.9

0

0.2

7

0.8

7

6

PT

FE

20

17

.20

3.3

2

1.6

0

18

.20

3.6

0

Al

1.0

0

0.2

8

1.3

3

1.3

7

0.2

6

7

PT

FE

20

17

.40

3.3

3

1.5

7

18

.50

3.6

1

Al

1.1

0

0.2

7

1.3

3

8

PT

FE

20

18

.20

3.3

0

1.5

6

19

.30

3.5

8

Al

1.1

0

0.2

8

0.9

5

9

PT

FE

20

17

.50

3.3

5

1.5

8

18

.50

3.6

3

Al

1.0

0

0.2

8

1.7

6

10

PT

FE

20

18

.10

3.3

4

1.5

7

19

.00

3.6

1

Al

0.9

0

0.2

7

1.5

0

11

PE

0

7.3

0

3.0

8

0.1

6

10

.00

3.3

3

Zn

2.7

0

0.2

5

0.6

2

0.4

9

0.0

7

12

PE

0

6.9

0

3.0

4

0.1

7

10

.00

3.3

0

Zn

3.1

0

0.2

6

0.4

6

13

PE

0

7.1

0

3.0

4

0.1

7

10

.20

3.3

0

Zn

3.1

0

0.2

6

0.4

2

14

PE

0

6.9

0

3.0

3

0.1

6

9.9

0

3.2

9

Zn

3.0

0

0.2

7

0.4

7

104

15

PE

0

6.6

0

3.0

6

0.1

9

9.5

0

3.3

1

Zn

2.9

0

0.2

6

0.4

8

16

PE

20

6.8

0

3.0

5

1.6

2

9.7

0

3.3

0

Zn

2.9

0

0.2

5

0.7

1

0.7

2

0.1

0

17

PE

20

7.1

0

3.0

8

1.6

0

10

.30

3.3

7

Zn

3.2

0

0.2

9

0.6

1

18

PE

20

7.0

0

3.0

6

1.5

7

10

.00

3.3

3

Zn

3.0

0

0.2

6

0.6

8

19

PE

20

7.2

0

3.0

9

1.6

0

10

.40

3.3

4

Zn

3.2

0

0.2

5

0.7

0

20

PE

20

7.0

0

3.0

5

1.5

7

10

.10

3.3

1

Zn

3.1

0

0.2

6

0.9

1

21

PT

FE

0

18

.00

3.3

4

0.1

7

21

.10

3.6

2

Zn

3.1

0

0.2

8

0.3

7

0.4

3

0.0

4

22

PT

FE

0

18

.50

3.3

4

0.1

5

21

.70

3.6

1

Zn

3.2

0

0.2

7

0.4

2

23

PT

FE

0

17

.50

3.3

1

0.1

4

20

.60

3.6

0

Zn

3.1

0

0.2

9

0.4

7

24

PT

FE

0

17

.70

3.2

9

0.1

6

20

.70

3.5

8

Zn

3.0

0

0.2

9

0.4

2

25

PT

FE

0

17

.90

3.3

2

0.1

7

21

.00

3.5

8

Zn

3.1

0

0.2

6

0.4

8

26

PT

FE

20

17

.20

3.3

3

1.5

7

20

.30

3.5

8

Zn

3.1

0

0.2

6

1.0

6

0.8

5

0.1

7

27

PT

FE

20

18

.20

3.3

5

1.5

6

21

.40

3.6

3

Zn

3.2

0

0.2

8

0.9

1

28

PT

FE

20

18

.40

3.3

6

1.5

7

21

.60

3.6

3

Zn

3.2

0

0.2

7

0.9

0

29

PT

FE

20

18

.00

3.3

1

1.5

6

21

.20

3.5

9

Zn

3.2

0

0.2

7

0.5

4

30

PT

FE

20

17

.70

3.3

5

1.5

9

20

.80

3.6

2

Zn

3.1

0

0.2

7

0.8

4

105

Adhesion Pull Tests: Coated Heated Substrates

The following table is the roughness tests prior to spraying and adhesion tests for the

heated substrates

Identification Virgin Sand Blasted

Sa

mp

le #

Ma

t

Gri

t #

C.

Ma

t

We

igh

t (g

)

Th

ick

ne

ss

(mm

)

Lo

ca

tio

n

Le

ft

Mid

dle

Rig

ht

Ra

_a

vg

(μm

)

Ra

_s

td (

μm

)

Le

ft

Mid

dle

Rig

ht

Ra

_a

vg

(μm

)

Ra

_s

td (

μm

)

1

PT

FE

0

Al

17

.4

3.1

3

To

p

0.5

9

0.6

0

0.5

9

0.6

0

0.0

6

- - - - -

Cen

ter

0.5

6

0.5

5

0.6

2

- - - - -

Bo

tto

m

0.6

8

0.6

9

0.5

1

- - - - -

2

PT

FE

0

Al

17

.3

3.1

3

To

p

0.5

1

0.6

1

0.6

3

0.5

6

0.0

8

- - - - -

Cen

ter

0.5

0

0.5

5

0.6

7

- - - - -

Bo

tto

m

0.4

2

0.5

3

0.6

5

- - - - -

3

PT

FE

0

Al

17

.1

3.1

2

To

p

0.5

0

0.6

2

0.5

8

0.6

5

0.0

8

- - - - -

Cen

ter

0.5

8

0.6

3

0.6

5

- - - - -

Bo

tto

m

0.7

6

0.7

6

0.7

3

- - - - -

4

PT

FE

20

Al

17

.1

3.1

5

To

p

0.5

5

0.6

9

0.7

8

0.7

1

0.1

0

1.6

8

1.7

1

1.6

2

1.6

4

0.0

5

Cen

ter

0.8

5

0.5

6

0.8

1

1.6

4

1.6

4

1.6

3

106

Bo

tto

m

0.7

1

0.7

7

0.6

4

1.5

5

1.5

5

1.7

0

5

PT

FE

20

Al

17

.8

3.1

1

To

p

0.8

1

0.9

1

0.9

1

0.8

5

0.0

5

1.6

0

1.5

0

1.5

9

1.5

6

0.0

7

Ce

nte

r

0.8

3

0.9

3

0.7

7

1.7

0

1.5

4

1.5

3

Bo

tto

m

0.8

3

0.8

1

0.8

6

1.4

5

1.5

8

1.5

5

6

PT

FE

20

Al

17

.6

3.1

3

To

p

0.5

9

0.7

7

0.6

8

0.7

3

0.0

6

1.7

0

1.5

5

1.5

3

1.6

0

0.0

7

Cen

ter

0.7

8

0.8

0

0.6

9

1.6

0

1.5

3

1.5

8

Bo

tto

m

0.7

7

0.7

5

0.7

3

1.6

4

1.7

3

1.5

2

7

PE

0

Zn

6.8

2.8

8

To

p

0.1

7

0.1

6

0.1

8

0.1

7

0.0

2

- - - - -

Cen

ter

0.1

7

0.2

3

0.1

7

- - - - -

Bo

tto

m

0.1

6

0.1

6

0.1

7

- - - - -

8

PE

0

Zn

7.0

2.8

7

To

p

0.1

7

0.1

8

0.1

5

0.1

7

0.0

1

- - - - -

Cen

ter

0.1

6

0.1

7

0.1

9

- - - - -

Bo

tto

m

0.1

9

0.1

8

0.1

7

- - - - -

9

PE

0

Zn

6.9

2.8

7

To

p

0.1

8

0.1

7

0.1

9

0.1

8

0.0

1

- - - - -

107

Ce

nte

r

0.1

7

0.1

6

0.1

8

- - - - -

Bo

tto

m

0.1

8

0.1

8

0.2

0

- - - - -

10

PE

20

Zn

7.0

2.9

2

To

p

0.3

9

0.4

2

0.3

0

0.4

0

0.0

4

1.6

3

1.5

3

1.5

7

1.5

9

0.0

7

Ce

nte

r

0.4

0

0.4

1

0.3

6

1.7

3

1.5

0

1.5

4

Bo

tto

m

0.4

2

0.4

3

0.4

4

1.6

1

1.5

5

1.6

6

11

PE

20

Zn

6.4

2.9

2

To

p

0.1

7

0.1

7

0.1

6

0.1

6

0.0

1

1.5

6

1.6

1

1.7

1

1.5

8

0.0

5

Cen

ter

0.1

8

0.1

5

0.1

7

1.5

7

1.6

0

1.5

3

Bo

tto

m

0.1

6

0.1

6

0.1

5

1.5

9

1.5

2

1.5

5

12

PE

20

Zn

6.9

2.9

5

To

p

0.1

6

0.1

7

0.1

4

0.1

5

0.0

1

1.6

7

1.5

7

1.5

7

1.5

9

0.0

7

Cen

ter

0.1

4

0.1

6

0.1

4

1.5

9

1.5

4

1.5

8

Bo

tto

m

0.1

4

0.1

4

0.1

3

1.4

9

1.5

5

1.7

6

13

PT

FE

0

Zn

17

.4

3.1

6

To

p

0.5

4

0.6

4

0.6

1

0.6

4

0.0

6

- - - - -

Cen

ter

0.6

5

0.5

8

0.6

5

- - - - -

Bo

tto

m

0.6

4

0.7

5

0.7

2

- - - - -

108

14

PT

FE

0

Zn

17

.3

3.1

7

To

p

0.5

5

0.6

4

0.7

0

0.6

1

0.0

9

- - - - -

Ce

nte

r

0.4

2

0.6

1

0.7

1

- - - - -

Bo

tto

m

0.5

3

0.6

8

0.6

5

- - - - -

15

PT

FE

0

Zn

17

.6

3.1

5

To

p

0.5

6

0.6

5

0.7

4

0.6

6

0.0

8

- - - - -

Cen

ter

0.5

9

0.6

4

0.7

1

- - - - -

Bo

tto

m

0.5

6

0.7

2

0.7

9

- - - - -

16

PT

FE

20

Zn

17

.2

3.1

6

To

p

0.7

1

0.6

6

0.9

0

0.7

8

0.0

7

1.6

4

1.5

7

1.7

2

1.6

0

0.0

6

Cen

ter

0.8

0

0.8

3

0.8

2

1.5

8

1.5

9

1.6

8

Bo

tto

m

0.7

9

0.7

7

0.7

7

1.5

5

1.5

4

1.5

7

17

PT

FE

20

Zn

17

.8

3.2

1

To

p

0.7

6

0.8

0

0.8

6

0.8

3

0.0

5

1.6

7

1.6

0

1.5

1

1.5

9

0.0

6

Cen

ter

0.8

1

0.8

3

0.8

1

1.5

3

1.6

6

1.5

6

Bo

tto

m

0.9

6

0.8

5

0.8

0

1.6

3

1.6

7

1.5

1

18

PT

FE

20

Zn

17

.5

3.1

6

To

p

0.8

5

0.8

0

0.8

1

0.8

2

0.0

2

1.6

3

1.6

4

1.6

0

1.5

8

0.0

5

Cen

ter

0.8

1

0.7

9

0.8

2

1.5

2

1.5

3

1.6

0

109

Bo

tto

m

0.8

4

0.8

3

0.8

6

1.5

7

1.4

9

1.6

3

The following table is the coating characteristics and adhesion tests performed for all

described samples.

Tests After Metallization Pull Test Data

Sa

mp

le #

Ma

teri

al

Co

atin

g

S.

Te

mp

(°C

)

We

ight

(g)

[Aft

er]

C.

We

igh

t (g

)

Th

ickn

ess (

mm

)

[Aft

er]

C.

Th

ickne

ss

(um

)

Ad

he

sio

n

Str

en

gth

(M

pa

)

Avg

_A

dh

esio

n

(Mp

a)

Avg

_D

ev (

Mp

a)

1

PT

FE

0

Al

11

5

18

.5

1.1

0

3.5

3

40

9.2

1.3

3

1.6

4

0.2

7

2

PT

FE

0

Al

18

.5

1.2

0

3.5

7

43

3.3

1.6

0

3

PT

FE

0

Al

18

.3

1.2

0

3.5

4

41

4.2

1.9

9

4

PT

FE

20

Al

18

.3

1.2

0

3.5

8

42

8.3

2.5

0

2.4

5

0.0

4

5

PT

FE

20

Al

18

.9

1.1

0

3.5

5

43

9.2

2.3

9

6

PT

FE

20

Al

18

.7

1.1

0

3.5

6

42

6.7

2.4

5

7

PE

0

Zn

50

10

.5

3.7

0

3.2

7

39

1.7

0.7

0

0.7

0

0.0

1

8

PE

0

Zn

10

.9

3.9

0

3.2

9

42

5.0

0.7

1

9

PE

0

Zn

10

.8

3.9

0

3.2

7

39

4.2

0.6

8

10

PE

20

Zn

10

.9

3.9

0

3.3

0

37

5.4

0.9

5

1.0

7

0.1

0

110

11

PE

20

Zn

10

.3

3.9

0

3.3

0

38

3.3

1.2

0

12

PE

20

Zn

10

.8

3.9

0

3.3

2

37

4.2

1.0

5

13

PT

FE

0

Zn

11

5

21

.1

3.7

0

3.5

5

38

8.3

0.7

5

0.7

5

0.0

2

14

PT

FE

0

Zn

20

.9

3.6

0

3.5

6

38

0.8

0.7

3

15

PT

FE

0

Zn

21

.4

3.8

0

3.5

4

39

0.0

0.7

8

16

PT

FE

20

Zn

21

.1

3.9

0

3.5

3

36

9.2

1.2

2

1.4

2

0.2

8

17

PT

FE

20

Zn

21

.7

3.9

0

3.5

7

36

4.2

1.8

2

18

PT

FE

20

Zn

21

.4

3.9

0

3.5

3

37

0.4

1.2

3

111

Appendix E

Design Drawings for Heating Unit

thermal spray deposition of metals on polymer substrates€¦ · characterization of metal-to...

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