can electroplated fe-c be an environmentally friendly ... · can electroplated fe-c be an...

Lars Pleth Nielsen, Tribology Center

Danish Technological Institute, Denmark

Can electroplated Fe-C be an environmentally friendly alternative to hard chromium and DLC coatings?

Can electroplated Fe-C be an environmentally

friendly alternative to hard chromium and DLC

coatings? Klaus Pagh Almtoft, Henrik Bækgaard,

Bjarke Hall Christensen, Jona Jacobsen,

Helle Iben Jensen, Christian Slot Jeppesen,

Lone Larsen, Jens Erik Lionett, Sascha Louring,

Claus Mathiasen, Dorthe Kjær Pedersen,

Preben Munch Pedersen, Kristian Rechendorff,

Henrik Horup Reitz, Jens Vestergaard

Prof. Per Møller

Dr.-Ing. Karen Pantleon

PhD student Jacob Obitsø Nielsen

A. H. Nichro Hardchrome

Timo J. Hakala, Helena Ronkainen,

Hanna Iitti, Jarkko Metsäjoki

Amaya Igartua

Francesco Pagano

Outline

■  Introduction – why is it interesting to find alternatives to Hard Chrome

■  Introduction to three different coatings:

•  Electroplating: •  New Fe-C coating

•  PVD: •  a-C:H •  a-C:H:Si

■  Temperature stability of the developed coatings

■  Friction properties: •  Scratch tests •  Pin-on-disk (air/vacuum)

■  Summary and conclusion

Take home messages:

•  DLC; air/vacuum

•  Adding Si to DLC

•  Hard Chrome

•  Highest friction

•  Highest wear

•  FeC interesting

hardness

Hard Chromium – facts: ■  High hardness

■  Large thickness - more than 100 µm

■  Large components up to metric tons

■  Process temperature is low compared with other type of processes like PVD and thermochemical diffusion processes

■  The coating is very corrosion resistant

■  Microcracks -> lubricants

■  The coating can be used as food contact material and is not able to introduce allergy

■  Easy release properties due to low surface energy

Wear resistance

Hardness

Tribological properties

Corrosion resistance

High temperature resistance

Magnetic properties

Electrical conductivity

Solderability/weldability/joining

Food contact material

Catalytic properties

Easy release properties

Hydrophobic/hydrophilic properties

Color and appearance

Decorative appearance

Refractive index

Optical properties

Oxide formation/passivation

Hard Chromium has many properties

Wear resistance

Hardness

Tribological properties

Corrosion resistance

High temperature resistance

Magnetic properties

Electrical conductivity

Solderability/weldability/joining

Food contact material

Catalytic properties

Easy release properties

Hydrophobic/hydrophilic properties

Color and appearance

Decorative appearance

Refractive index

Optical properties

Oxide formation/passivation

Difficult to replace

with one unique

solution

The future of Hard Chromium

■  Hexavalent chromium need an authorization since it is listed on the REACH Annex XIV.

■  REACH is an abbreviation for Registration, Evaluation, Authorization and Restriction of Chemicals.

■  REACH entered into force in 1 June 2007, with a phased implementation over the next decade. The regulation also established the European Chemicals Agency, which manages the technical, scientific and administrative aspects of REACH.

The future of Hard Chromium

■  The sunset date for using chromium trioxide (Cr+VI) in Europe is September 21, 2017. After this date it is no longer allowed to use hexavalent chromium for any production in the surface treatment field without having an authorization.

■  March 21, 2016 is the latest date to apply for a such authorization. If an authorization is required it is specific to a substance and its application(s).

However, it is unique; Fink -

1925

Fink and Eldridge - 1924

Break through at Columbia

University and commercialize

the process

Printing rollers - 1928

Chromium

Copper

Steel

Possible alternatives:

Electroplating: Fe-C

PVD-DLC’s: a-C:H a-C:H:Si

Lets compare these coatings…

Electroplating: Fe-C

Possible alternatives:

Fe-C coating ■  Electrolyte: FeSO4 + stabalizing agent

■  Anode: Inert; Ti-Pt

■  Temperature: 30 - 60 °C

■  Current Efficiency ≈ 80% ■  Main difficulties being:

! Oxidation by air ! Varying pH level

Anode: Fe -> Fe2+ + 2e-

Cathode: Fe2+ + 2e- -> Fe

FeC coating, 24 hours – no adjustments

■  Stability: Continues plating for 24 hour in a 25L container

■  No adjustment made….

■  Stable pH ± 0,05

■  Electrolyte fully reduced

Rate: ~23 µm/h

PVD-DLC’s: a-C:H a-C:H:Si

Possible alternatives:

Introduction to PVD ■  Industrial unit (CC 800/9-Custom)

■  Reactive DC magnetron sputtering ■  DC/MF substrate bias

■  Deposition parameters: ■  a-C:H (C, Cr) ■  a-C:H:Si (C, Cr, Si) ■  Adhesion layer of CrN

■  Ar/N2/C2H2

■  Deposition temperature ~200°C

■  Thickness ~ 3 µm inc. adhesion layer

Substrates Targets/ cathodes

Literature; a-C:H

■  DLC doped with hydrogen; a-C:H

■  Often best under dry atmosphere or under vacuum

■  Low friction is caused by electrostatic repulsion of mating surfaces

■  Often 30 at. % hydrogen or higher -> superlubricity under vacuum -  COF < 0.01

■  Limited temperature stability

•  ~ 200 oC -> graphitization •  Depending on composition, structure and doping

Literature; a-C:H:Si

■  Improved performance by adding Si to a-C:H

■  Tribological performance is less dependent on the environment -> COF below 0.05 at atmospheric pressure in a wide range of temperatures and humilities

■  The improved performance under humid conditions is ascribed to the

catalytic activity of Si dopants for surface hydroxylation -> formation of a lubricating water film

■  Increasing Si content: -> increase the total number of sp3 Si-C bonds -> increase hardness - more diamond like

■  Improved temperature stability

Introduction to PVD; a-C:H and a-C:H:Si

a-C:H a-

C:H:Si

CrN

Gradient

DLC

Substrate

Characterization/Properties:

Electroplating: Fe-C

Results – GDOES

Average carbon content of 0.85

wt%

Results – XRD; as deposited

Ferrite with very

small amount of

Fe2O3

Results – SEM; Cross-section

As deposited

Results – XRD; as deposited

Annealed at 205 ℃ for 1 hour Annealed at 315 ℃ for 1 hour

Results – SEM; Cross-section

205 °C-1h 315 °C-1h

As deposited

Results – TEM diffraction pattern

Tag Phase hkl d-spacing [Å] 1 Unidentified 3.13

2 Unidentified 2.61

3 Ferrite 110 2.12

4 Ferrite 200 1.48

5 Unidentified 1.21

Tag Phase hkl d-spacing [Å] 1 β-Fe2O3 013 4.05

2 Unidentified 3.02

3 Unidentified 2.60

4 β-Fe2O3 018 2.43

5 Ferrite 110 2.06

6 β-Fe2O3 11-11 1.65

7 Unidentified 1.52

As deposited

Results – TEM diffraction pattern

315°C-1h

Results – TEM diffraction pattern

Tag Phase hkl d-spacing [Å] 1 Unidentified 3.13

2 Unidentified 2.61

3 Ferrite 110 2.12

4 Ferrite 200 1.48

5 Unidentified 1.21

Tag Phase hkl d-spacing [Å] 1 β-Fe2O3 013 4.05

2 Unidentified 3.02

3 Unidentified 2.60

4 β-Fe2O3 018 2.43

5 Ferrite 110 2.06

6 β-Fe2O3 11-11 1.65

7 Unidentified 1.52

Tag Phase hkl d-spacing [Å]

1 β-Fe2O3 104 3.67

2 Unidentified 3.11

3 Unidentified 2.67

4 β-Fe2O3 11-5 2.36

5 Cohenite 201 2.22

6 Ferrite 110 2.11

7 Fe3O4 422 1.71

8 β-Fe2O3 21-6 1.64

9 Cohenite 301 1.60

10 Unidentified 1.55

11 Ferrite 200 1.49

12 Cohenite 123 1.31

13 Unidentified 1.22

As deposited 315°C-1h

Ferrite + undefined -> Ferrite, β-Fe2O3, Cohenite (Fe3C) +

undefined phases

Results – TEM diffraction pattern

Results – Hardness, FeC Future-tech microhardness tester FM-700.

Hardness maintained up 300 oC

■  High deposition rate ~23 µm/h

■  High hardness - 750 HV

■  Stable up to 300 oC

■  As deposited Ferrite + undefined phase

■  Heating to 300 oC -> Ferrite, β-Fe2O3, Cohenite (Fe3C) + undefined phases

Conclusion on, FeC

Sample As deposited 300 oC a-C:H:Si 2200 HV 2100 HV a-C:H 1600 HV Delaminated FeC 7.4 7.4

Results – Hardness, DLC’er ■  Annealing; 300° C for 2 hours in air.

500 1000 1500 2000 25000

1000

2000

3000

4000

5000

6000

7000

8000

Intens

ity(co

unts)

R amans hift(cm -1)

500 1000 1500 2000 25000

200

400

600

800

1000

1200

Intens

ity(co

unts)

R amans hift(cm -1)

�  Graphitisation + change in mechanical properties " not temperature stable

D: sp2

G: sp3

Sample As deposited 300 oC a-C:H:Si 2200 HV 2100 HV a-C:H 1600 HV Delaminated FeC 7.4 7.4

G-peak

position (cm-1)

FWHM(G)

(cm-1)

I(D)/IG)

As made 1551±0.4 175±0.6 1.14±0.01

annealed 1561±0.3 157±0.4 1.41±0.01

Results – Hardness, DLC’er

•  Decrease of FWHM -> ordering

•  Increase in I(D)/I(G) increase in sp2 cluster size

■  Annealing; 300° C for 2 hours in air.

�  Graphitisation + change in mechanical properties " not temperature stable

a-C:H hardness maintained up < 200 oC

a-C:H:Si hardness maintained up

~300 oC

■  Higher hardness than FeC ■  a-C:H; 1600 HV ■  a-C:H:Si; 2200 HV

■  Temperature stability;

■  a-C:H; ~200 oC ■  a-C:H:Si; ~300 oC

Conclusion on a-C:H and a-C:Si

Mechanical and Friction properties:

Scratch test parameters.

•  Scratch tip: Rockwell C, R 200 µm

•  Progressive load: 0.10 – 30 N

•  Scratch length: 10 mm

•  Scratch speed: 10 mm/min

•  Scratch spacing: > 1 mm

•  Loading rate: 29.90 N/min

•  Prescan, postscan: 0.10 N

•  Environment: 22±1 °C, 50±5 % RH

•  # of scratches per specimen: 3 Substrate: DIN X155CrVMo12-1

Scratch test

Lc1 = 45° crack

Lc2 = edge delamination

Lc5 = crack formed on the bottom of the

scratch grove

Scratch test, Hard Chrome (100 µm)

Scratch test, FeC (thick) Lc1 very difficult to see

Lc2 = edge delamination

Lc5 = crack formed on the

bottom of the scratch grove,

which continues until the end of

the scratch

Fe-C thick:

Fe-C thin:

Lc1 Lc2

1 8.4 -

2 8.6 -

3 6.0 -

Average 7.7 -

STDEV 1.4 -

Lc1 Lc2

1 5.4 18.2

2 4.8 19.3

3 6 16.9

Average 5.4 18.1

STDEV 0.6 1.2

Scratch test, FeC (thick and thin)

Scratch test, DLC-TR (a-C:H)

Scratch test; Si-DLC (a-C:H:Si)

0.1 N 30 N

Scratch test

Results – Pin-on-disk experiments

■  Pin-on-Disc tribometer designed and manufactured at VTT

■  Test parameters: •  AISI420 for all coatings •  +Al2O3 for FeC and Si-DLC •  Normal load 5 N •  Sliding velocity 0.637 m/s •  Duration 4 hours •  Sliding track diameter

•  34 mm (85742 cycles) •  29 mm (100525 cycles)

FeC delaminated under the tests

conditions due to adhesion to the

ball (AISI420 / Al2O3)

Results – Wear

■  After tribological experiments the wear tracks were measured by 2D-profilometry

■  Wear track of the coated surface was

measured

■  Optical microscopy was used to measure the diameter of the worn surface on stainless steel balls after experiments

Results – Wear

■  COF was determined as the average value between 120-180 minutes of sliding

Results – Coefficient of friction (COF)

Sample COF Std a-C:H:Si (AISI420) 0.084 0.015 a-C:H:Si (Al2O3) 0.098 0.038 a-C:H 0.131 0.010 Hard Chrome 90 µm 0.890 0.017

■  TL: formation of tribolayer

Results – Wear

Sample Wear (mm3/Nm)

Std wear

a-C:H:Si (AISI420) 5.585E-07 5.40E-08 a-C:H:Si (Al2O3) 5.100E-07 5.40E-08 a-C:H 1.781E-07 5.62E-08 Hard Chrome 90 µm 1.124E-5 1.89E-06

Results – Wear rates

Results – Wear; air versus vacuum

Mass-spectrometer

Leak valve

Load-lock chamber

Main chamber

Sample transfer rod Tribometer

The UHV tribometer, allows to study behavior of materials, coatings and lubricants both in ultra high vacuum (P < 1x10-7 Pa) and in controlled environments.

2N

12N

Normal air:

2N

12N

Vacuum:

Air: a-C:H:Si lowest friction for

both loads

Results – Wear; air versus vacuum

Vacuum: a-C:H

lowest

Friction as a function of pressure a-C:H

a-C:H

a-C:H:Si

Friction of a-C:H:Si is much more pressure

dependent

Summary ■  FeC:

■  High hardness around 750 HV ■  Stable up to ~300 oC ■  High content of homogeneously distributed carbon ■  Cracking under pressure if it too thin

■  Scratch tests:

■  a-C:H coating deforms and does not crack ■  a-C:H:Si has a different failure mechanism as compared to a-C:H ■  Lc1 values decreases with increasing Hard Chrome thickness ■  Thick FeC delaminate

■  Pin-on-Disk

■  a-C:H:Si has the lowest friction in air ■  a-C:H reveals pressure dependent friction ■  a-C:H has the lowest wear rate ■  FeC coatings showed adhesive failures ■  Hard Chrome has high wear

Lars Pleth Nielsen, Director Tribology Center Danish Technological Institute Email: lpn@dti.dk Phone: +45 72201585

Wear: a-C:H < a-C:H:Si << Hard

Chrome

Temperature stability: a-C:H < a-C:H:Si < FeC <

Hard Chrome

Friction in air: a-C:H:Si < a-C:H << Hard

Chrome Friction in vacuum: a-C:H < a-C:H:Si << Hard

Chrome

Thick FeC + DLC might be an interesting alternative

Just send an email if you are interested in testing

our coatings