June 18, 2013 2
Introduction
• Scratch Test - Introduction
• Various Types of scratch tests
• Brief description of Bruker UMT- Scratch Test Module
• Deciding on test type, tip, and test parameters
• Scratch test applications using Bruker UMT - Magnetic disk, PCB,
Laser-printed surface, Plant Leaf, Painted surface
• Summary
• Q & A
June 18, 2013 3
Introduction
Scratch is a simple, practical, and
quick test. A stylus with well-defined
tip geometry is moved over a
specimen surface with load until
failure occurs at critical load or loads
𝐿𝑐𝑖 . Normal force (Fz) and Lateral
force (Fx) are recorded.
Critical load depends on coating-
substrate adhesion, stylus-tip radius,
Scratch Direction
Load
Stylus
loading rate, mechanical properties of substrate and coating, coating
thickness, internal stress in coating, flaw population and density, and friction
between stylus-tip and coating.
Scratch is further examined by an optical microscope to understand failure
events. AE and ECR measured during scratch test.
June 18, 2013 4
Scratch Test
Scratch is widely used for Research, Development, and Quality Control of
bulk and coatings. The knowledge of damage mechanism through a
scratch test is useful to understand material-process-property relations. It
is also used as a supporting tool for Failure Analysis of engineering
components.
For Bulk Materials:
(a) To obtain scratch hardness
(b) To evaluate resistance against deterioration of surface quality during
handling and in real-life applications.
For Coating:
(a) To estimate practical adhesion strength of coating for various
applications (protective, decorative, tribological, optical, biological, etc.)
(b) To understand failure modes of coating and coating-substrate interface
June 18, 2013 5
Scratch Test – Major Types
Constant Load scratch test provides better differentiation of damage
levels. Such test requires more specimens area and test time, it is used
for research and process development of coatings.
Progressive Load scratch test covers full load range with a single test
without any gap, therefore, it is faster than Constant Load test. It is the
most popular test for R&D and QC of coating.
June 18, 2013 8
Selecting Parameters and Tip
Scratch Variables:
Type of scratch - Constant Load or Progressive Load
Load - initial and final load
Velocity and Scratch Length - Loading rate
Tip - materials, shape, and size
Choice of scratch variables depends on:
Mechanical properties of the substrate and coating
Adhesion strength of the coating to the substrate
Coating thickness
Single/multi-layer coating
Scratch characterization: Imaging and Metrology
June 18, 2013 9
Bruker Universal Materials Tester (UMT)
Bruker Universal Materials Tester (UMT) is a unique test and measurement system that can be used for Scratch Testing: (a) Constant load: Unidirectional and X-Y (b) Progressive load: Linear and Zig-zag • ECR, ESR, AE measurements • in-situ scratch depth profiling (capacitance sensor, tip-displacement) • Optical Microcopy and AFM for automated imaging • 3D-Optical Microscopy for metrology
June 18, 2013 10
Bruker UMT
• Carriage:
– provides Z-motion
– houses the Slider
• Slider :
– houses Force Sensor
– mounts Scratching Tool
– provides X-motion
– Optical/AFM/3D Microscope
• Lower Drive:
– Y-motion for scratching
– mounts Coated Specimen
Z
Y
X
June 18, 2013 11
Force Sensors and Scratching Tools
Force Sensors:
• FVL : 1 to 100 mN • FL : 5 to 500 mN • DFM series (3 ranges) : 0.05 to 20 N • DFH series (3 ranges): 0.5 to 200 N
Scratching Tool:
• Diamond stylus: 2.5, 5, and 12.5 mm tip radius • Rockwell indenter: 200 mm tip radius with 120o cone angle • Knoop Indenter: with two apex angle (130o and 172o50/) • Microblade: tungsten carbide, diamond (400 mm tip radius)
June 18, 2013 12
Unidirectional Scratch
Tool: Knoop Indenter
Scratch Parameters: 5 mm at 50mm/s; Load 4N (Constant)
Specimen 1 Specimen 2
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X-Y Scratch
Specimen: 3.5-mm thick DLC coating on steel substrate.
Tool: Diamond stylus with 12.5-mm tip radius
Scratch Parameters: X-Y; 120-mm long; spacing 60,40,30,20,15,10,5 mm;
at 0.01 mm/s; Load 250 mN (constant)
June 18, 2013 14
Linear Scratch
Tool: Diamond Stylus (12.5 mm radius)
Scratch Parameters: 2 mm at 10 mm/s; Load 2-150 mN
Coating 1 Coating 2
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Zig-zag Scratch
Specimen: 3.5-mm thick DLC coating on steel substrate.
Tool: Diamond stylus 12.5-mm tip radius
Scratch Parameters: 1 mm by slider at 0.004 mm/s; 0.15mm stroke by
linear at 0.15 mm/s; Load 20 to 250 mN; Coating failed at 245 mN
June 18, 2013 16
Scratch for Adhesion Energy
Specimen: Polymer dots (1.2 mm dia x 25 mm) on ceramic substrate.
Tool: Tool-steel micro-blade; Adhesion Energy calculated from area of
the triangle under Fx plot. Adhesion Energy: 490 erg
X [ um ]
-300 -200 -100 0 100 200 300
Z [
um
]
-5
0
5
10
15
20
25
June 18, 2013 18
Scratch Test on Magnetic Disk
Magnetic disk has a lube layer on top
followed by a sub-micron thick
carbonaceous layer (DLC) on a magnetic
substrate to:
- protect the disk from scratch, corrosion
- maintains low friction, high hardness,
high elasticity
- improves lube compatibility
- reduces surface roughness
• Linear and Zig-zag scratch tests were performed with a Rockwell indenter
• Surface and Scratch was evaluated using a Bruker 3D Microscope
June 18, 2013 19
Linear Scratch Test on Magnetic Disk
Specimen: Lube layer + DLC on Metallic substrate
Tool: Rockwell indenter (200-mm tip radius)
Scratch Parameters: Linear; 2 mm at 10mm/s; Load 0.5 to 20 N; Coating
failed at 9.2 N; COF changed at failure but was Not very clear !
June 18, 2013 21
Zig-zag Scratch Test on Magnetic Disk
Specimen: Lube layer + DLC (3-mm thick) on Metallic substrate
Tool: Rockwell indenter (200-mm tip radius)
Scratch Parameters: Zigzag; 2 mm at 4 mm/s; Stroke 0.3 mm at 300 mm/s; Load 0.5 to 20
N; Coating failed at 7.3 N; Both COF and AE changed at Failure.
Regime -1 : removal of
top lube layer
Regime -2: failure of DLC
layer (Bluish tint)-
increasing COF and AE
Regime -3: scratching
magnetic layer
underneath DLC; High
COF and AE activity
June 18, 2013 26
Scratch Test on PCB
• Copper coating (20mm-thick) on glass-epoxy
composite substrate
• Scratch test was performed with a WC
microblade and Rockwell indenter. Load 0.5 to
20 N; Linear scratch: 1 mm 20 mm/s; Zigzag
Scratch; 2 mm at 4 mm/s; Stroke 0.3 mm at 300
mm/s.
June 18, 2013 27
Scratch test on Cu-PCB
Specimen: Copper coating (PCB)
Tool: WC microblade (400-mm tip radius)
Scratch Parameters: Linear; 1 mm at 20mm/s; Load 0.5 to 15 N; Coating
failed at 11.9 N; AE activity at failure.
June 18, 2013 28
Scratch test on Cu-PCB
Specimen: Copper coating (PCB)
Tool: Rockwell (200-mm tip radius)
Scratch Parameters: Zigzag; 2 mm at 4 mm/s; Stroke 0.3 mm at
0.3mm/s; Load 0.5 to 20 N; Coating failed at 10.1 N; AE activity at
failure.
June 18, 2013 29
Optical Image of the end of Scratch
Specimen: Copper coating (PCB);
Image size- 816 mm x 612 mm
Tool: Rockwell (200-mm tip radius)
Scratch Parameters: Zigzag; 2 mm at 4
mm/s; Stroke 0.3 mm at 0.3mm/s; Load
0.5 to 20 N; Coating failed at 10.1 N.
June 18, 2013 31
Laser-Printed-layer
Step-height
Measurement
Scratch Test
Scratch test was performed on the green printed area using a Bruker UMT sensor
and a diamond stylus (12.5 mm tip radius).
Surface Roughness, Step-height, and scratch depth profile measurements were
performed using a 3D Microscope.
Green pattern was printed on a white
paper using a Laser Color Printer (Model
- Xerox® Phaser 8560).
June 18, 2013 32
Surface Roughness
Sa, mm Sz, mm
Blank 3.12 37.73
Green Print 0.80 10.49
Blank Surface Green Printed Surface
Surface Roughness
June 18, 2013 33
Thickness of the Printed-layer
Step-height measurement across the edge of the Green print and blank
paper. The thickness of the laser print is about 10 mm.
Green Blank
June 18, 2013 34
Scratch test on Laser-Printed-layer
Specimen: 10-mm thick Green Laser printed layer on paper
Tool: Diamond stylus 12.5-mm tip radius
Scratch Parameters: Linear; 1 mm at 0.01 mm/s; Load 0.5 to 10 mN;
Coating failed at 1.65 mN
June 18, 2013 35
Scratch Depth Profile Printed Layer
Depth profile of the scratch on Green Laser printed layer on paper
June 18, 2013 37
Some insects scratch and suck green leaves of
plant to harness Pyrrolizidine Alkaloids (PAs) which
are available as sap underneath the top layer. The
PA, thus gathered, is used by these insects for
biosynthesis of Pheromone.
Scratching Plant epidermis of Leaf
June 18, 2013 38
Top and Bottom Sides of a Green Leaf
Top surface (adaxial) Bottom surface (abaxial)
Top epidermis
Bottom epidermis
Mesophyll
Cross section of a leaf (Schematic)
June 18, 2013 39
Surface Roughness of Green Leaf
Sa, mm Sz, mm
Top Surface 3.35 24.83
Bottom Surface 2.21 59.99
Bottom Surface (abaxial) Top Surface (adaxial)
Bottom surface has stomata (porous structure) that leads to increase in Sz
than the top surface. Shiny top surface hints the presence of wax.
Surface Roughness
June 18, 2013 40
Bottom Side of Green Leaf
Bottom Surface of the Green leaf has round porous structure about 20mm
radius and 20mm deep.
June 18, 2013 41
Scratch test on Top Side of Green Leaf
Specimen: Top Surface of a Green Leaf
Tool: Diamond stylus 12.5-mm tip radius
Scratch Parameters: Linear; 1 mm at 0.01 mm/s; Load 0.5 to 30 mN;
Top surface failed at 17.9 mN
June 18, 2013 42
Scratch test on Bottom Side of Green Leaf
Specimen: Bottom Surface of a Green Leaf
Tool: Diamond stylus 12.5-mm tip radius
Scratch Parameters: Linear; 1 mm at 0.01 mm/s; Load 0.5 to 30 mN;
Top surface failed at 11.5 mN
June 18, 2013 44
Scratch test on Painted Surface
Specimen: Top Surface of Paint (~70 mm thick)
Tool: Microblade 400-mm tip radius
Scratch Parameters: Linear; 4 mm at 0.05 mm/s; Load 0.5 to 20 N;
Top surface failed at 7.7 N
June 18, 2013 45
In-situ Scratch Depth Profile
Specimen: Top Surface of Paint (~70 mm thick)
Tool: Microblade 400-mm tip radius
Scratch Parameters: Linear; 4 mm at 0.05 mm/s; Load 0.5 to 20 N;
Top surface failed at 7.7 N
June 18, 2013 46
Summary
• Scratch test is an important tool for Research, Development, and Quality Control activities related to engineering, biological, and biomedical applications.
• Bruker Universal Materials Tester (UMT) is capable of performing advanced scratch test with automated optical imaging and metrology for comprehensive evaluation of bulk and coating materials.