Tribology 101 - Advanced Scratch Testing Applications -Suresh Kuiry, Ph.D.

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 6

Scratch Test – Constant Load

Constant Load

• Unidirectional

• X-Y

June 18, 2013 7

Scratch Test – Progressive Load

Progressively Increasing Load

• Linear

• Zig-zag

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

June 18, 2013 13

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

June 18, 2013 15

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 17

UMT Scratch Test Applications:

Scratch Test on Magnetic disk

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 20

Scratch Depth Profile

Depth profile of the Linear scratch on Magnetic Disk

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 22

Depth Profile – Regime 1

June 18, 2013 23

Depth Profile – Regime 2

June 18, 2013 24

Depth Profile – Regime 3

June 18, 2013 25

UMT Scratch Test Applications:

Copper Coating on PCB

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 30

UMT Scratch Test Applications:

Laser-printed Surface

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 36

UMT Scratch Test Applications:

Plant Leaf

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 43

UMT Scratch Test Applications:

Painted Surface

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.

© Copyright Bruker Corporation. All rights reserved.

www.bruker.com