Tribology 101 - Advanced Scratch Testing Applications -Suresh Kuiry, Ph.D.
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 2
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 Lc i. Normal force (Fz) and Lateral force (Fx) are recorded. Stylus Load Scratch Direction Critical load depends on coatingsubstrate adhesion, stylus-tip radius, 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 3
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 4
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 5
Scratch Test Constant Load Constant Load Unidirectional X-Y June 18, 2013 6
Scratch Test Progressive Load Progressively Increasing Load Linear Zig-zag June 18, 2013 7
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 8
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 9
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 Y Z X June 18, 2013 10
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 120 o cone angle Knoop Indenter: with two apex angle (130 o and 172 o 50 / ) Microblade: tungsten carbide, diamond (400 mm tip radius) June 18, 2013 11
Unidirectional Scratch Specimen 1 Specimen 2 Tool: Knoop Indenter Scratch Parameters: 5 mm at 50mm/s; Load 4N (Constant) June 18, 2013 12
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 13
Linear Scratch Coating 1 Coating 2 Tool: Diamond Stylus (12.5 mm radius) Scratch Parameters: 2 mm at 10 mm/s; Load 2-150 mn June 18, 2013 14
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 15
Z [um] Scratch for Adhesion Energy 25 20 15 10 5 0-5 -300-200 -100 0 100 200 300 X [ um ] 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 June 18, 2013 16
UMT Scratch Test Applications: Scratch Test on Magnetic disk June 18, 2013 17
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 18
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 19
Scratch Depth Profile Depth profile of the Linear scratch on Magnetic Disk June 18, 2013 20
Zig-zag Scratch Test on Magnetic Disk 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 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. June 18, 2013 21
Depth Profile Regime 1 June 18, 2013 22
Depth Profile Regime 2 June 18, 2013 23
Depth Profile Regime 3 June 18, 2013 24
UMT Scratch Test Applications: Copper Coating on PCB June 18, 2013 25
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 26
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 27
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 28
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 29
UMT Scratch Test Applications: Laser-printed Surface June 18, 2013 30
Laser-Printed-layer Step-height Measurement Scratch Test Green pattern was printed on a white paper using a Laser Color Printer (Model - Xerox Phaser 8560). 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. June 18, 2013 31
Surface Roughness Blank Surface Green Printed Surface Surface Roughness Sa, mm Sz, mm Blank 3.12 37.73 Green Print 0.80 10.49 June 18, 2013 32
Thickness of the Printed-layer Green Blank Step-height measurement across the edge of the Green print and blank paper. The thickness of the laser print is about 10 mm. June 18, 2013 33
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 34
Scratch Depth Profile Printed Layer Depth profile of the scratch on Green Laser printed layer on paper June 18, 2013 35
UMT Scratch Test Applications: Plant Leaf June 18, 2013 36
Scratching Plant epidermis of Leaf 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. June 18, 2013 37
Top and Bottom Sides of a Green Leaf Top surface (adaxial) Bottom surface (abaxial) Cross section of a leaf (Schematic) Top epidermis Mesophyll Bottom epidermis June 18, 2013 38
Surface Roughness of Green Leaf Top Surface (adaxial) Bottom Surface (abaxial) Surface Roughness Sa, mm Sz, mm Top Surface 3.35 24.83 Bottom Surface 2.21 59.99 Bottom surface has stomata (porous structure) that leads to increase in Sz than the top surface. Shiny top surface hints the presence of wax. June 18, 2013 39
Bottom Side of Green Leaf Bottom Surface of the Green leaf has round porous structure about 20mm radius and 20mm deep. June 18, 2013 40
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 41
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 42
UMT Scratch Test Applications: Painted Surface June 18, 2013 43
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 44
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 45
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. June 18, 2013 46
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