Category: Application Notes

Nano Scratch & Mar Testing of Paint on Metal Substrate

Nano Scratch & Mar Testing

of Paint on Metal Substrate

Prepared by

SUSANA CABELLO

INTRODUCTION

Paint with or without hard coat is one of the most commonly used coatings. We see it on cars, on walls, on appliances and virtually anything that needs some protective coatings or simply for aesthetic purposes. The paints that are meant for the protection of the underlying substrate often have chemicals that prevent the paint from catching on fire or simply that prevent it from losing its color or cracking. Often the paint used for aesthetic purposes comes in various colors, but may not be necessarily meant for the protection of its substrate or for a long lifetime.

Nevertheless, all paint suﬀers some weathering over time. Weathering on paint can often change the properties from what the makers intended it to have. It can chip quicker, peel oﬀ with heat, loose color or crack. The diﬀerent property changes of paint over time is why makers oﬀer such a wide selection. Paints are tailored to meet diﬀerent requirements for individual clients.

IMPORTANCE OF NANO SCRATCH TESTING FOR QUALITY CONTROL

A major concern for paint makers is the ability for their product to withstand cracking. Once paint begins to crack, it fails to protect the substrate that it was applied on; therefore, failing to satisfy their client. For example, if a branch happens to stroke the side of a car and immediately after the paint begins to chip oﬀ the makers of the paint would lose business due to their poor quality of paint. The quality of the paint is very important because if the metal under the paint becomes exposed it may begin to rust or corrode due to its new exposure.

Reasons like this apply to several other spectrums such as household and office supplies and electronics, toys, research tools and more. Although the paint may be resistant to cracking when they first apply it to metal coatings, the properties may change over time when some weathering has occurred on the sample. This is why it’s very important to have the paint samples tested at their weathered stage. Although cracking under a high load of stress may be inevitable, the maker must predict how weakening the changes may be over time and how deep the aﬀecting scratch must be in order to provide their consumers with the best possible products.

MEASUREMENT OBJECTIVE

We must simulate the process of scratching in a controlled and monitored manner to observe sample behavior eﬀects. In this application, the NANOVEA PB1000 Mechanical Tester in Nano Scratch Testing mode is used to measure the load required to cause failure to an approximately 7 year old 30-50 μm thick paint sample on a metal substrate.

A 2 μm diamond tipped stylus is used at a progressive load ranging from 0.015 mN to 20.00 mN to scratch the coating. We performed a pre and post scan of the paint with 0.2 mN load in order to determine the value for the true depth of the scratch. The true depth analyzes the plastic and elastic deformation of the sample during testing; whereas, the post-scan only analyzes the plastic deformation of the scratch. The point where the coating fails by cracking is taken as the point of failure. We used the ASTMD7187 as a guide to determine our testing parameters.

We can conclude that having used a weathered sample; therefore, testing a paint sample at its weaker stage, presented us with lower points of failure.

Five tests were performed on this sample in order to

determine the exact failure critical loads.

NANOVEA

PB1000

TEST PARAMETERS

following ASTM D7027

The surface of a Roughness Standard was scanned using a NANOVEA ST400 equipped with a high-speed sensor that generates a bright line of 192 points, as shown in FIGURE 1. These 192 points scan the sample surface at the same time, leading to significantly increased scan speed.

LOAD TYPE	Progressive
INITIAL LOAD	0.015 mN
FINAL LOAD	20 mN
LOADING RATE	20 mN/min
SCRATCH LENGTH	1.6 mm
SCRATCH SPEED, dx/dt	1.601 mm/min
PRE-SCAN LOAD	0.2 mN
POST-SCAN LOAD	0.2 mN

indenter type

Conical

Diamond 90° Cone

2 µm tip radius

RESULTS

This section presents the data collected on the failures during the scratch test. The first section describes the failures observed in the scratch and defines the critical loads that were reported. The next part contains a summary table of the critical loads for all samples, and a graphical representation. The last part presents detailed results for each sample: the critical loads for each scratch, micrographs of each failure, and the graph of the test.

FAILURES OBSERVED AND DEFINITION OF CRITICAL LOADS

CRITICAL FAILURE:

INITIAL DAMAGE

This is the first point at which the damage is observed along the scratch track.

CRITICAL FAILURE:

COMPLETE DAMAGE

At this point, the damage is more significant where the paint is chipping and cracking along the scratch track.

DETAILED RESULTS

* Failure values taken at point of substrate cracking.

CRITICAL LOADS
SCRATCH	INITIAL DAMAGE [mN]	COMPLETE DAMAGE [µm]
1	14.513	4.932
2	3.895	4.838
3	3.917	4.930

AVERAGE	3.988	4.900
STD DEV	0.143	0.054

FIGURE 2: Micrograph of Full Scratch (1000x magniﬁcation).

FIGURE 3: Micrograph of Initial Damage (1000x magniﬁcation).

FIGURE 4: Micrograph of Complete Damage (1000x magniﬁcation).

FIGURE 5: Friction Force and Coeﬃcient of Friction.

FIGURE 6: Surface Profile.

FIGURE 7: True Depth and Residual Depth.

CONCLUSION

The NANOVEA Mechanical Tester in the Nano Scratch Tester mode allows the simulation of many real-life failures of paint coatings and hard coats. By applying increasing loads in a controlled and closely monitored manner, the instrument allows to identify at what load failures occur. This can then be used as a way to determine quantitative values for scratch resistance. The coating tested, with no weathering, is known to have a first crack at about 22 mN. With values closer to 5 mN, it is clear that the 7 year lap has degraded the paint.

Compensating for the original profile allows obtaining corrected depth during the scratch and measuring the residual depth after the scratch. This gives extra information on the plastic versus elastic behavior of the coating under increasing load. Both cracking and the information on deformation can be of great use for improving the hard coat. The very small standard deviations also show the reproducibility of the instrument’s technique which can help manufacturers improve the quality of their hard coat/paint and study weathering eﬀects.

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Roughness Mapping Inspection using 3D Profilometry

ROUGHNESS MAPPING INSPECTION

USING 3D PROFILOMETRY

Prepared by

DUANJIE, PhD

INTRODUCTION

Surface roughness and texture are critical factors that impact the final quality and performance of a product. A thorough understanding of surface roughness, texture, and consistency is essential for selecting the best processing and control measures. Fast, quantifiable, and reliable inline inspection of product surfaces is in need to identify the defective products in time and optimize production line conditions.

IMPORTANCE OF 3D NON-CONTACT PROFILOMETER FOR IN-LINE SURFACE INSPECTION

Surface defects in products result from materials processing and product manufacturing. Inline surface quality inspection ensures the tightest quality control of the end products. NANOVEA 3D Non-Contact Optical Profilers utilize Chromatic Light technology with unique capability to determine the roughness of a sample without contact. The line sensor enables scanning of the 3D profile of a large surface at a high speed. The roughness threshold, calculated in real-time by the analysis software, serves as a fast and reliable pass/fail tool.

MEASUREMENT OBJECTIVE

In this study, the NANOVEA ST400 equipped with a high-speed sensor is used to inspect the surface of a Teﬂon sample with defect to showcase the capability of NANOVEA

Non-Contact Proﬁlometers in providing fast and reliable surface inspection in a production line.

NANOVEA

ST400

RESULTS & DISCUSSION

3D Surface Analysis of the Roughness Standard Sample

FIGURE 2 shows false color views of the Surface Height Map and Roughness Distribution Map of the Roughness Standard Sample. In FIGURE 2a, the Roughness Standard exhibits a slightly slanted surface as represented by the varied color gradient in each of the standard roughness blocks. In FIGURE 2b, homogeneous roughness distribution is shown in diﬀerent roughness blocks, the color of which represents the roughness in the blocks.

FIGURE 3 shows the examples of the Pass/Fail Maps generated by the Analysis Software based on diﬀerent Roughness Thresholds. The roughness blocks are highlighted in red when their surface roughness is above a certain set threshold value. This provides a tool for the user to set up a roughness threshold to determine the quality of a sample surface finish.

FIGURE 1: Optical line sensor scanning on the Roughness Standard sample

a. Surface Height Map:

b. Roughness Map:

FIGURE 2: False color views of the Surface Height Map and Roughness Distribution Map of the Roughness Standard Sample.

FIGURE 3: Pass/Fail Map based on the Roughness Threshold.

Surface Inspection of a Teﬂon Sample with Defects

Surface Height Map, Roughness Distribution Map and Pass/Fail Roughness Threshold Map of the Teﬂon sample surface are shown in FIGURE 4. The Teﬂon Sample has a ridge form at the right center of the sample as shown in the Surface Height Map.

a. Surface Height Map:

The diﬀerent colors in the pallet of FIGURE 4b represents the roughness value on the local surface. The Roughness Map exhibits a homogeneous roughness in the intact area of the Teﬂon sample. However, the defects, in the forms of an indented ring and a wear scar are highlighted in bright color. The user can easily set up a Pass/Fail roughness threshold to locate the surface defects as shown in FIGURE 4c. Such a tool allows users to monitor in situ the product surface quality in the production line and discover defective products in time. The real-time roughness value is calculated and recorded as the products pass by the in-line optical sensor, which can serve as a fast but reliable tool for quality control.

b. Roughness Map:

c. Pass/Fail Roughness Threshold Map:

FIGURE 4: Surface Height Map, Roughness Distribution Map and Pass/Fail Roughness Threshold Map of the Teﬂon sample surface.

CONCLUSION

In this application, we have shown how the NANOVEA ST400 3D Non-Contact Optical Profiler equipped with an optical line sensor works as a reliable quality control tool in an eﬀective and efficient manner.

The optical line sensor generates a bright line of 192 points that scan the sample surface at the same time, leading to significantly increased scan speed. It can be installed in the production line to monitor the surface roughness of the products in situ. The roughness threshold works as a dependable criteria to determine the surface quality of the products, allowing users to notice the defective products in time.

The data shown here represents only a portion of the calculations available in the analysis software. NANOVEA Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.

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High Temperature Scratch Hardness using a Tribometer

HIGH TEMPERATURE SCRATCH HARDNESS

USING A TRIBOMETER

Prepared by

DUANJIE, PhD

INTRODUCTION

Hardness measures the resistance of materials to permanent or plastic deformation. Originally developed by a German mineralogist Friedrich Mohs in 1820, scratch hardness test determines the hardness of a material to scratches and abrasion due to friction from a sharp object¹. The Mohs’ scale is a comparative index rather than a linear scale, therefore a more accurate and qualitative scratch hardness measurement was developed as described in ASTM standard G171-03². It measures the average width of the scratch created by a diamond stylus and calculates the scratch hardness number (HSP).

IMPORTANCE OF SCRATCH HARDNESS MEASUREMENT AT HIGH TEMPERATURES

Materials are selected based on the service requirements. For applications involving significant temperature changes and thermal gradients, it is critical to investigate the mechanical properties of materials at high temperatures to be fully aware of the mechanical limits. Materials, especially polymers, usually soften at high temperatures. A lot of mechanical failures are caused by creep deformation and thermal fatigue taking place only at elevated temperatures. Therefore, a reliable technique for measuring hardness at high temperatures is in need to ensure proper selection of the materials for high temperature applications.

MEASUREMENT OBJECTIVE

In this study, the NANOVEA T50 Tribometer measures scratch hardness of a Teflon sample at different temperatures from room temperature to 300ºC. The capability of performing high temperature scratch hardness measurement makes the NANOVEA Tribometer a versatile system for tribological and mechanical evaluations of materials for high temperature applications.

NANOVEA

T50

TEST CONDITIONS

The NANOVEA T50 Free Weight Standard Tribometer was used to perform the scratch hardness tests on a Teflon sample at temperatures ranging from room temperature (RT) to 300°C. Teflon has a melting point of 326.8°C. A conical diamond stylus of apex angle 120° with tip radius of 200 µm was used. The Teflon sample was fixed on the rotative sample stage with a distance of 10 mm to the stage center. The sample was heated up by an oven and tested at temperatures of RT, 50°C, 100°C, 150°C, 200°C, 250°C and 300°C.

TEST PARAMETERS

of the high temperature scratch hardness measurement

NORMAL FORCE	2 N
SLIDING SPEED	1 mm/s
SLIDING DISTANCE	8mm per temp
ATMOSPHERE	Air
TEMPERATURE	RT, 50°C, 100°C, 150°C, 200°C, 250°C, 300°C.

RESULTS & DISCUSSION

The scratch track profiles of the Teflon sample at different temperatures are shown in FIGURE 1 in order to compare the scratch hardness at different elevated temperatures. The material pile-up on the scratch track edges forms as the stylus travels at a constant load of 2 N and ploughs into the Teflon sample, pushing and deforming the material in the scratch track to the side.

The scratch tracks were examined under the optical microscope as shown in FIGURE 2. The measured scratch track widths and calculated scratch hardness numbers (HSP) are summarized and compared in FIGURE 3. The scratch track width measured by the microscope is in agreement with that measured using the NANOVEA Profiler – the Teflon sample exhibits a wider scratch width at higher temperatures. Its scratch track width increases from 281 to 539 µm as the temperature elevates from RT to 300oC, resulting in decreased HSP from 65 to 18 MPa.

The scratch hardness at elevated temperatures can be measured with high precision and repeatability using the NANOVEA T50 Tribometer. It provides an alternative solution from other hardness measurements and makes NANOVEA Tribometers a more complete system for comprehensive high-temperature tribo-mechanical evaluations.

FIGURE 1: Scratch track profiles after the scratch hardness tests at different temperatures.

FIGURE 2: Scratch tracks under the microscope after the measurements at different temperatures.

FIGURE 3: Evolution of the scratch track width and scratch hardness vs. the temperature.

CONCLUSION

In this study, we showcase how the NANOVEA Tribometer measures the scratch hardness at elevated temperatures in compliance to ASTM G171-03. The scratch hardness test at a constant load provides an alternative simple solution for comparing the hardness of materials using the tribometer. The capacity of performing scratch hardness measurements at elevated temperatures makes the NANOVEA Tribometer an ideal tool for evaluating the high temperature tribo-mechanical properties of materials.

The NANOVEA Tribometer also offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. Optional 3D non-contact profiler is available for high resolution 3D imaging of wear tracks in addition to other surface measurements such as roughness.

1 Wredenberg, Fredrik; PL Larsson (2009). “Scratch testing of metals and polymers: Experiments and numerics”. Wear 266 (1–2): 76
2 ASTM G171-03 (2009), “Standard Test Method for Scratch Hardness of Materials Using a Diamond Stylus”

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Weld Surface Inspection Using a Portable 3D Profilometer

WELd surface inspection

using a portable 3d profilometer

Prepared by

CRAIG LEISING

INTRODUCTION

It may become critical for a particular weld, typically done by visual inspection, to be investigated with an extreme level of precision. Specific areas of interest for precise analysis include surface cracks, porosity and unfilled craters, regardless of subsequent inspection procedures. Weld characteristics such as dimension/shape, volume, roughness, size etc. can all be measured for critical evaluation.

IMPORTANCE OF 3D NON-CONTACT PROFILOMETER FOR WELD SURFACE INSPECTION

Unlike other techniques such as touch probes or interferometry, the NANOVEA 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any surface, sample sizes can vary widely due to open staging and there is no sample preparation needed. Nano through macro range is obtained during surface profile measurement with zero influence from sample reflectivity or absorption, has advanced ability to measure high surface angles and there is no software manipulation of results. Easily measure any material: transparent, opaque, specular, diffusive, polished, rough etc. The 2D and 2D capabilities of the NANOVEA Portable Profilometers make them ideal instruments for full complete weld surface inspection both in the lab and in the field.

MEASUREMENT OBJECTIVE

In this application, the NANOVEA JR25 Portable Profiler is used to measure the surface roughness, shape and volume of a weld, as well as the surrounding area. This information can provide critical information to properly investigate the quality of the weld and weld process.

NANOVEA

JR25

TEST RESULTS

The image below shows the full 3D view of the weld and the surrounding area along with the surface parameters of the weld only. The 2D cross section profile is shown below.

the sample

With the above 2D cross section profile removed from the 3D, dimensional information of the weld is calculated below. Surface area and volume of material calculated for the weld only below.

	HOLE	PEAK
SURFACE	1.01 mm²	14.0 mm²
VOLUME	8.799e-5 mm³	23.27 mm³
MAX DEPTH/HEIGHT	0.0276 mm	0.6195 mm
MEAN DEPTH/HEIGHT	0.004024 mm	0.2298 mm

CONCLUSION

In this application, we have shown how the NANOVEA 3D Non-Contact Profiler can precisely characterize critical characteristics of a weld and the surrounding surface area. From the roughness, dimensions and volume, a quantitative method for quality and repeatability can be determined and or further investigated. Sample welds, such as the example in this app note, can be easily analyzed, with a standard tabletop or portable NANOVEA Profiler for in-house or field testing

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Industrial Coatings Scratch and Wear Evaluation

INDUSTRIAL COATING

SCRATCH AND WEAR EVALUATION USING A TRIBOMETER

Prepared by

DUANJIE LI, PhD & ANDREA HERRMANN

INTRODUCTION

Acrylic urethane paint is a type of fast-dry protective coating widely used in a variety of industrial applications, such as floor paint, auto paint, and others. When used as floor paint, it can serve areas with heavy foot and rubber-wheel traffic, such as walkways, curbs and parking lots.

IMPORTANCE OF SCRATCH AND WEAR TESTING FOR QUALITY CONTROL

Traditionally, Taber abrasion tests were carried out to evaluate the wear resistance of acrylic urethane floor paint according to the ASTM D4060 standard. However, as mentioned in the standard, “For some materials, abrasion tests utilizing the Taber Abraser may be subject to variation due to changes in the abrasive characteristics of the wheel during testing.”1 This may result in poor reproducibility of test results and create difficulty in comparing values reported from different laboratories. Moreover, in Taber abrasion tests, abrasion resistance is calculated as loss in weight at a specified number of abrasion cycles. However, acrylic urethane floor paints have a recommended dry film thickness of 37.5-50 μm2.

The aggressive abrasion process by Taber Abraser can quickly wear through the acrylic urethane coating and create mass loss to the substrate leading to substantial errors in the calculation of the paint weight loss. The implant of abrasive particles in the paint during the abrasion test also contributes to errors. Therefore, a well-controlled quantifiable and reliable measurement is crucial to ensure reproducible wear evaluation of the paint. In addition, the scratch test allows users to detect premature adhesive/cohesive failures in real-life applications.

MEASUREMENT OBJECTIVE

In this study, we showcase that NANOVEA Tribometers and Mechanical Testers are ideal for evaluation and quality control of industrial coatings.

The wear process of acrylic urethane floor paints with different topcoats is simulated in a controlled and monitored manner using the NANOVEA Tribometer. Micro scratch testing is used to measure the load required to cause cohesive or adhesive failure to the paint.

NANOVEA T100

The Compact Pneumatic Tribometer

NANOVEA PB1000

The Large Platform Mechanical Tester

TEST PROCEDURE

This study evaluates four commercially available water-based acrylic floor coatings that have the same primer (basecoat) and different topcoats of the same formula with a small alternation in the additive blends for the purpose of enhancing durability. These four coatings are identified as Samples A, B, C and D.

WEAR TEST

The NANOVEA Tribometer was applied to evaluate the tribological behavior, e.g. coefficient of friction, COF, and wear resistance. A SS440 ball tip (6 mm dia., Grade 100) was applied against the tested paints. The COF was recorded in situ. The wear rate, K, was evaluated using the formula K=V/(F×s)=A/(F×n), where V is the worn volume, F is the normal load, s is the sliding distance, A is the cross-sectional area of the wear track, and n is the number of revolution. Surface roughness and wear track profiles were evaluated by the NANOVEA Optical Profilometer, and the wear track morphology was examined using optical microscope.

WEAR TEST PARAMETERS

NORMAL FORCE

20 N

SPEED

15 m/min

DURATION OF TEST

100, 150, 300 & 800 cycles

SCRATCH TEST

The NANOVEA Mechanical Tester equipped with a Rockwell C diamond stylus (200 μm radius) was used to perform progressive load scratch tests on the paint samples using the Micro Scratch Tester Mode. Two final loads were used: 5 N final load for investigating paint delamination from the primer, and 35 N for investigating primer delamination from the metal substrates. Three tests were repeated at the same testing conditions on each sample to ensure reproducibility of the results.

Panoramic images of the whole scratch lengths were automatically generated and their critical failure locations were correlated with the applied loads by the system software. This software feature facilitates users to perform analysis on the scratch tracks any time, rather than having to determine the critical load under the microscope immediately after the scratch tests.

SCRATCH TEST PARAMETERS

LOAD TYPE	Progressive
INITIAL LOAD	0.01 mN
FINAL LOAD	5 N / 35 N
LOADING RATE	10 / 70 N/min
SCRATCH LENGTH	3 mm
SCRATCHING SPEED, dx/dt	6.0 mm/min
INDENTER GEOMETRY	120º cone
INDENTER MATERIAL (tip)	Diamond
INDENTER TIP RADIUS	200 μm

WEAR TEST RESULTS

Four pin-on-disk wear tests at different number of revolutions (100, 150, 300 and 800 cycles) were performed on each sample in order to monitor the evolution of wear. The surface morphology of the samples were measured with a NANOVEA 3D Non-Contact Profiler to quantify the surface roughness prior to conducting wear testing. All samples had a comparable surface roughness of approximately 1 μm as displayed in FIGURE 1. The COF was recorded in situ during the wear tests as shown in FIGURE 2. FIGURE 4 presents the evolution of wear tracks after 100, 150, 300 and 800 cycles, and FIGURE 3 summarized the average wear rate of different samples at different stages of the wear process.

Compared with a COF value of ~0.07 for the other three samples, Sample A exhibits a much higher COF of ~0.15 at the beginning, which gradually increases and gets stable at ~0.3 after 300 wear cycles. Such a high COF accelerates the wear process and creates a substantial amount of paint debris as indicated in FIGURE 4 – the topcoat of Sample A has started to be removed in the first 100 revolutions. As shown in FIGURE 3, Sample A exhibits the highest wear rate of ~5 μm2/N in the first 300 cycles, which slightly decreases to ~3.5 μm2/N due to the better wear resistance of the metal substrate. The topcoat of Sample C starts to fail after 150 wear cycles as shown in FIGURE 4, which is also indicated by the increase of COF in FIGURE 2.

In comparison, Sample B and Sample D show enhanced tribological properties. Sample B maintains a low COF throughout the whole test – the COF slightly increases from~0.05 to ~0.1. Such a lubricating effect substantially enhances its wear resistance – the topcoat still provides superior protection to the primer underneath after 800 wear cycles. The lowest average wear rate of only ~0.77 μm2/N is measured for Sample B at 800 cycles. The topcoat of Sample D starts to delaminate after 375 cycles, as reflected by the abrupt increase of COF in FIGURE 2. The average wear rate of Sample D is ~1.1 μm2/N at 800 cycles.

Compared to the conventional Taber abrasion measurements, NANOVEA Tribometer provides well-controlled quantifiable and reliable wear assessments that ensure reproducible evaluations and quality control of commercial floor/auto paints. Moreover, the capacity of in situ COF measurements allow users to correlate the different stages of a wear process with the evolution of COF, which is critical in improving fundamental understanding of the wear mechanism and tribological characteristics of various paint coatings.

FIGURE 1: 3D morphology and roughness of the paint samples.

FIGURE 2: COF during pin-on-disk tests.

FIGURE 3: Evolution of wear rate of different paints.

FIGURE 4: Evolution of wear tracks during the pin-on-disk tests.

SCRATCH TEST RESULTS

FIGURE 5 shows the plot of normal force, frictional force and true depth as a function of scratch length for Sample A as an example. An optional acoustic emission module can be installed to provide more information. As the normal load linearly increases, the indentation tip gradually sinks into the tested sample as reflected by the progressive increase of true depth. The variation in the slopes of frictional force and true depth curves can be used as one of the implications that coating failures start to occur.

FIGURE 5: Normal force, frictional force and true depth as a function of scratch length for scratch test of Sample A with a maximum load of 5 N.

FIGURE 6 and FIGURE 7 show the full scratches of all four paint samples tested with a maximum load of 5 N and 35 N, respectively. Sample D required a higher load of 50 N to delaminate the primer. Scratch tests at 5 N final load (FIGURE 6) evaluate the cohesive/adhesive failure of the top paint, while the ones at 35 N (FIGURE 7) assess the delamination of the primer. The arrows in the micrographs indicate the point at which the top coating or the primer start to be completely removed from the primer or the substrate. The load at this point, so called Critical Load, Lc, is used to compare the cohesive or adhesive properties of the paint as summarized in Table 1.

It is evident that the paint Sample D has the best interfacial adhesion – exhibiting the highest Lc values of 4.04 N at paint delamination and 36.61 N at primer delamination. Sample B shows the second best scratch resistance. From the scratch analysis, we show that optimization of the paint formula is critical to the mechanical behaviors, or more specifically, scratch resistance and adhesion property of acrylic floor paints.

Table 1: Summary of critical loads.

FIGURE 6: Micrographs of full scratch with 5 N maximum load.

FIGURE 7: Micrographs of full scratch with 35 N maximum load.

CONCLUSION

Compared to the conventional Taber abrasion measurements, the NANOVEA Mechanical Tester and Tribometer are superior tools for evaluation and quality control of commercial floor and automotive coatings. The NANOVEA Mechanical Tester in Scratch mode can detect adhesion/cohesion problems in a coating system. The NANOVEA Tribometer provides well-controlled quantifiable and repeatable tribological analysis on wear resistance and coefficient of friction of the paints.

Based on the comprehensive tribological and mechanical analyses on the water based acrylic floor coatings tested in this study, we show that Sample B possesses the lowest COF and wear rate and the second best scratch resistance, while Sample D exhibits the best scratch resistance and second best wear resistance. This assessment allows us to evaluate and select the best candidate targeting the needs in different application environments.

The Nano and Micro modules of the NANOVEA Mechanical Tester all include ISO and ASTM compliant indentation, scratch and wear tester modes, providing the widest range of testing available for paint evaluation on a single module. The NANOVEA Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. NANOVEA’s unmatched range is an ideal solution for determining the full range of mechanical/tribological properties of thin or thick, soft or hard coatings, films and substrates, including hardness, Young’s modulus, fracture toughness, adhesion, wear resistance and many others. Optional NANOVEA Non-Contact Optical Profilers are available for high resolution 3D imaging of scratchs and wear tracks in addition to other surface measurements such as roughness.

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Scratch Hardness Measurement using Mechanical Tester

SCRATCH HARDNESS MEASUREMENT

USING A MECHANICAL TESTER

Prepared by

DUANJIE LI, PhD

INTRODUCTION

In general, hardness tests measure the resistance of materials to permanent or plastic deformation. There are three types of hardness measurements: scratch hardness, indentation hardness and rebound hardness. A scratch hardness test measures a material’s resistance to scratch and abrasion due to friction from a sharp object1. It was originally developed by German mineralogist Friedrich Mohs in 1820 and is still widely used to rank the physical properties of minerals2. This test method is also applicable to metals, ceramics, polymers, and coated surfaces.

During a scratch hardness measurement, a diamond stylus of specified geometry scratches into a material’s surface along a linear path under a constant normal force with a constant speed. The average width of the scratch is measured and used to calculate the scratch hardness number (HSP). This technique provides a simple solution for scaling the hardness of different materials.

MEASUREMENT OBJECTIVE

In this study, the NANOVEA PB1000 Mechanical Tester is used to measure the scratch hardness of different metals in compliance with ASTM G171-03.

Simultaneously, this study showcases the capacity of the NANOVEA Mechanical Tester in performing scratch hardness measurement with high precision and reproducibility.

NANOVEA

PB1000

TEST CONDITIONS

The NANOVEA PB1000 Mechanical Tester performed scratch hardness tests on three polished metals (Cu110, Al6061 and SS304). A conical diamond stylus of apex angle 120° with tip radius of 200 µm was used. Each sample was scratched three times with the same test parameters to ensure reproducibility of the results. The test parameters are summarized below. A profile scan at a low normal load of 10 mN was performed before and after the scratch test to measure the change in the surface profile of the scratch.

TEST PARAMETERS

NORMAL FORCE

10 N

TEMPERATURE

24°C (RT)

SLIDING SPEED

20 mm/min

SLIDING DISTANCE

10 mm

ATMOSPHERE

Air

RESULTS & DISCUSSION

The images of the scratch tracks of three metals (Cu110, Al6061 and SS304) after the tests are shown in FIGURE 1 in order to compare the scratch hardness of different materials. The mapping function of the NANOVEA Mechanical Software was used to create three parallel scratches tested under the same condition in an automated protocol. The measured scratch track width and calculated scratch hardness number (HSP) are summarized and compared in TABLE 1. The metals show different wear track widths of 174, 220 and 89 µm for Al6061, Cu110 and SS304, respectively, resulting in a calculated HSP of 0.84, 0.52 and 3.2 GPa.

In addition to the scratch hardness computed from the scratch track width, the evolution of coefficient of friction (COF), true depth and acoustic emission were recorded in situ during the scratch hardness test. Here, the true depth is the depth difference between the penetration depth of the stylus during the scratch test and the surface profile measured in the pre-scan. The COF, true depth and acoustic emission of Cu110 are shown in FIGURE 2 as an example. Such information provides insight into mechanical failures taking place during scratching, enabling users to detect mechanical defects and further investigate the scratch behavior of the tested material.

The scratch hardness tests can be finished within a couple of minutes with high precision and repeatability. Compared to conventional indentation procedures, the scratch hardness test in this study provides an alternative solution for hardness measurements, which is useful for quality control and the development of new materials.

Al6061

Cu110

SS304

FIGURE 1: Microscope image of the scratch tracks post test (100x magnification).

	*Scratch track width (μm)*	*HS_p (GPa)*
Al6061	174±11	0.84
Cu110	220±1	0.52
SS304	89±5	3.20

TABLE 1: Summary of scratch track width and scratch hardness number.

FIGURE 2: The evolution of coefficient of friction, true depth and acoustic emissions during the scratch hardness test on Cu110.

CONCLUSION

In this study, we showcased the capacity of the NANOVEA Mechanical Tester in performing scratch hardness tests in compliance to ASTM G171-03. In addition to coating adhesion and scratch resistance, the scratch test at a constant load provides an alternative simple solution for comparing the hardness of materials. In contrast to conventional scratch hardness testers, NANOVEA Mechanical Testers offer optional modules for monitoring the evolution of coefficient of friction, acoustic emission and true depth in situ.

The Nano and Micro modules of a NANOVEA Mechanical Tester include ISO and ASTM compliant indentation, scratch and wear tester modes, providing the widest and most user-friendly range of testing available in a single system. NANOVEA’s unmatched range is an ideal solution for determining the full range of mechanical properties of thin or thick, soft or hard coatings, films and substrates, including hardness, Young’s modulus, fracture toughness, adhesion, wear resistance and many others.

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Titanium Nitride Coating Scratch Test

TITANIUM NITRIDE COATING SCRATCH TEST

QUALITY CONTROL INSPECTION

Prepared by

DUANJIE LI, PhD

INTRODUCTION

The combination of high hardness, excellent wear resistance, corrosion resistance and inertness makes titanium nitride (TiN) an ideal protective coating for metal components in various industries. For example, the edge retention and corrosion resistance of a TiN coating can substantially increase the work efficiency and extend the service life of machine tooling such as razor blades, metal cutters, injection molds and saws. Its high hardness, inertness and non-toxicity make TiN a great candidate for applications in medical devices including implants and surgical instruments.

IMPORTANCE OF TiN COATING SCRATCH TESTING

Residual stress in protective PVD/CVD coatings plays a critical role in the performance and mechanical integrity of the coated component. The residual stress derives from several major sources, including growth stress, thermal gradients, geometric constraints and service stress¹. The thermal expansion mismatch between the coating and the substrate created during coating deposition at elevated temperatures leads to high thermal residual stress. Moreover, TiN coated tools are often used under very high concentrated stresses, e.g. drill bits and bearings. It is critical to developing a reliable quality control process to quantitatively inspect the cohesive and adhesive strength of protective functional coatings.

[1] V. Teixeira, Vacuum 64 (2002) 393–399.

MEASUREMENT OBJECTIVE

In this study, we showcase that the NANOVEA Mechanical Testers in Scratch Mode are ideal for assessing the cohesive/adhesive strength of protective TiN coatings in a controlled and quantitative manner.

NANOVEA

PB1000

TEST CONDITIONS

The NANOVEA PB1000 Mechanical Tester was used to perform coating scratch tests on three TiN coatings using the same test parameters as summarized below:

LOADING MODE: Progressive Linear

INITIAL LOAD

0.02 N

FINAL LOAD

10 N

LOADING RATE

20 N/min

SCRATCH LENGTH

5 mm

INDENTER TYPE

Sphero-Conical

Diamond, 20 μm radius

RESULTS & DISCUSSION

FIGURE 1 shows the recorded evolution of penetration depth, coefficient of friction (COF) and acoustic emission during the test. The full micro scratch tracks on the TiN samples are shown in FIGURE 2. The failure behaviors at different critical loads are displayed in FIGURE 3, where critical load Lc1 is defined as the load at which the first sign of cohesive crack occurs in the scratch track, Lc2 is the load after which repeated spallation failures take place, and Lc3 is the load at which the coating is completely removed from the substrate. The critical load (Lc) values for the TiN coatings are summarized in FIGURE 4.

The evolution of penetration depth, COF and acoustic emission provides insight into the mechanism of the coating failure at different stages, which are represented by the critical loads in this study. It can be observed that Sample A and Sample B exhibit comparable behavior during the scratch test. The stylus progressively penetrates into the sample to a depth of ~0.06 mm and the COF gradually increases to ~0.3 as the normal load increases linearly at the beginning of the coating scratch test. When the Lc1 of ~3.3 N is reached, the first sign of chipping failure occurs. This is also reflected in the first large spikes in the plot of penetration depth, COF and acoustic emission. As the load continues to increase to Lc2 of ~3.8 N, further fluctuation of the penetration depth, COF and acoustic emission takes place. We can observe continuous spallation failure present on both sides of the scratch track. At the Lc3, the coating completely delaminates from the metal substrate under the high pressure applied by the stylus, leaving the substrate exposed and unprotected.

In comparison, Sample C exhibits lower critical loads at different stages of the coating scratch tests, which is also reflected in the evolution of penetration depth, coefficient of friction (COF) and acoustic emission during the coating scratch test. Sample C possesses an adhesion interlayer with lower hardness and higher stress at the interface between the top TiN coating and the metal substrate compared to Sample A and Sample B.

This study demonstrates the importance of proper substrate support and coating architecture to the quality of the coating system. A stronger interlayer can better resist deformation under a high external load and concentration stress, and thus enhance the cohesive and adhesive strength of the coating/substrate system.

FIGURE 1: Evolution of penetration depth, COF and acoustic emission of the TiN samples.

FIGURE 2: Full scratch track of the TiN coatings after the tests.

FIGURE 3: TiN coating failures under different critical loads, Lc.

FIGURE 4: Summary of critical load (Lc) values for the TiN coatings.

CONCLUSION

In this study, we showcased that the NANOVEA PB1000 Mechanical Tester performs reliable and accurate scratch tests on TiN-coated samples in a controlled and closely monitored manner. Scratch measurements allow users to quickly identify the critical load at which typical cohesive and adhesive coating failures occur. Our instruments are superior quality control tools that can quantitatively inspect and compare the intrinsic quality of a coating and the interfacial integrity of a coating/substrate system. A coating with a proper interlayer can resist large deformation under a high external load and concentration stress, and enhance the cohesive and adhesive strength of a coating/substrate system.

The Nano and Micro modules of a NANOVEA Mechanical Tester all include ISO and ASTM compliant indentation, scratch and wear tester modes, providing the widest and most user-friendly range of testing available in a single system. NANOVEA’s unmatched range is an ideal solution for determining the full range of mechanical properties of thin or thick, soft or hard coatings, films and substrates, including hardness, Young’s modulus, fracture toughness, adhesion, wear-resistance and many others.

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Fractography Analysis Using 3D Profilometry

FRACTOGRAPHY ANALYSIS

USING 3D PROFILOMETRY

Prepared by

CRAIG LEISING

INTRODUCTION

Fractography is the study of features on fractured surfaces and has historically been investigated via Microscope or SEM. Depending on the size of the feature, a microscope (macro features) or SEM (nano and micro features) are selected for the surface analysis. Both ultimately allowing for the identification of the fracture mechanism type. Although effective, the Microscope has clear limitations and the SEM in most cases, other than atomic-level analysis, is unpractical for fracture surface measurement and lacks broader use capability. With advances in optical measurement technology, the NANOVEA 3D Non-Contact Profilometer is now considered the instrument of choice, with its ability to provide nano through macro-scale 2D & 3D surface measurements

IMPORTANCE OF 3D NON-CONTACT PROFILOMETER FOR FRACTURE INSPECTION

Unlike an SEM, a 3D Non-Contact Profilometer can measure nearly any surface, sample size, with minimal sample prep, all while offering superior vertical/horizontal dimensions to that of an SEM. With a profiler, nano through macro range features are captured in a single measurement with zero influence from sample reflectivity. Easily measure any material: transparent, opaque, specular, diffusive, polished, rough etc. The 3D Non-Contact Profilometer provides broad and user-friendly capability to maximize surface fracture studies at a fraction of the cost of an SEM.

MEASUREMENT OBJECTIVE

In this application, the NANOVEA ST400 is used to measure the fractured surface of a steel sample. In this study, we will showcase a 3D area, 2D profile extraction and surface directional map of the surface.

NANOVEA

ST400

RESULTS

TOP SURFACE

3D Surface Texture Direction

Isotropy	51.26%
First Direction	123.2º
Second Direction	116.3º
Third Direction	0.1725º

Surface Area, Volume, Roughness and many others can be automatically calculated from this extraction.

2D Profile Extraction

RESULTS

SIDE SURFACE

3D Surface Texture Direction

Isotropy	15.55%
First Direction	0.1617º
Second Direction	110.5º
Third Direction	171.5º

Surface Area, Volume, Roughness and many others can be automatically calculated from this extraction.

2D Profile Extraction

CONCLUSION

In this application, we have shown how the NANOVEA ST400 3D Non-Contact Profilometer can precisely characterize the full topography (nano, micro and macro features) of a fractured surface. From the 3D area, the surface can be clearly identified and subareas or profiles/cross-sections can be quickly extracted and analyzed with an endless list of surface calculations. Sub nanometer surface features can be further analyzed with an integrated AFM module.

Additionally, NANOVEA has included a portable version to their Profilometer line-up, especially critical for field studies where a fracture surface is immovable. With this broad list of surface measurement capabilities, fracture surface analysis has never been easier and more convenient with a single instrument.

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Fiberglass Surface Topography Using 3D Profilometry

FIBERGLASS SURFACE TOPOGRAPHY

USING 3D PROFILOMETRY

Prepared by

CRAIG LEISING

INTRODUCTION

Fiberglass is a material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called “fiberglass” in popular usage.

IMPORTANCE OF SURFACE METROLOGY INSPECTION FOR QUALITY CONTROL

Although there are many uses for Fiberglass reinforcement, in most applications it is crucial that they are as strong as possible. Fiberglass composites have one of the highest strength to weight ratios available and in some cases, pound for pound it is stronger than steel. Aside from high strength, it is also important to have the smallest possible exposed surface area. Large fiberglass surfaces can make the structure more vulnerable to chemical attack and possibly material expansion. Therefore, surface inspection is critical to quality control production.

MEASUREMENT OBJECTIVE

In this application, the NANOVEA ST400 is used to measure a Fiberglass Composite surface for roughness and flatness. By quantifying these surface features it is possible to create or optimize a stronger, longer lasting fiberglass composite material.

NANOVEA

ST400

MEASUREMENT PARAMETERS

PROBE	1 mm
ACQUISITION RATE	300 Hz
AVERAGING	1
MEASURED SURFACE	5 mm x 2 mm
STEP SIZE	5 µm x 5 µm
SCANNING MODE	Constant speed

PROBE SPECIFICATIONS

**MEASUREMENT RANGE**	1 mm
Z RESOLUTION	25 nm
Z ACCURACY	200 nm
LATERAL RESOLUTION	2 μm

RESULTS

FALSE COLOR VIEW

3D Surface Flatness

3D Surface Roughness

Sa	15.716 μm	Arithmetical Mean Height
Sq	19.905 μm	Root Mean Square Height
Sp	116.74 μm	Maximum Peak Height
Sv	136.09 μm	Maximum Pit Height
Sz	252.83 μm	Maximum Height
Ssk	0.556	Skewness
Ssu	3.654	Kurtosis

CONCLUSION

As shown in the results, the NANOVEA ST400 Optical Profiler was able to accurately measure the roughness and flatness of the fiberglass composite surface. Data can be measured over multiple batches of fiber composites and or a given time period to provide crucial information about different fiberglass manufacturing processes and how they react over time. Thus, the ST400 is a viable option for strengthening the quality control process of fiberglass composite materials.

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Polymer Belt Wear and Friction using a Tribometer

POLYMER BELTS

WEAR AND FRICTION USING a TRIBOMETER

Prepared by

DUANJIE LI, PhD

INTRODUCTION

Belt drive transmits power and tracks relative movement between two or more rotating shafts. As a simple and inexpensive solution with minimal maintenance, belt drives are widely used in a variety of applications, such as bucksaws, sawmills, threshers, silo blowers and conveyors. Belt drives can protect the machinery from overload as well as damp and isolate vibration.

IMPORTANCE OF WEAR EVALUATION FOR BELT DRIVES

Friction and wear are inevitable for the belts in a belt-driven machine. Sufficient friction ensures effective power transmission without slipping, but excessive friction may rapidly wear the belt. Different types of wear such as fatigue, abrasion and friction take place during the belt drive operation. In order to extend the lifetime of the belt and to cut the cost and time on belt repairing and replacement, reliable evaluation of the wear performance of the belts is desirable in improving belt lifespan, production efficiency and application performance. Accurate measurement of the coefficient of friction and wear rate of the belt facilitates R&D and quality control of belt production.

MEASUREMENT OBJECTIVE

In this study, we simulated and compared the wear behaviors of belts with different surface textures to showcase the capacity of the NANOVEA T2000 Tribometer in simulating the wear process of the belt in a controlled and monitored manner.

NANOVEA

T2000

TEST PROCEDURES

The coefficient of friction, COF, and the wear resistance of two belts with different surface roughness and texture were evaluated by the NANOVEA High-Load Tribometer using Linear Reciprocating Wear Module. A Steel 440 ball (10 mm diameter) was used as the counter material. The surface roughness and wear track were examined using an integrated 3D Non-Contact profilometer. The wear rate, K, was evaluated using the formula K=Vl(Fxs), where V is the worn volume, F is the normal load and s is the sliding distance.

Please note that a smooth Steel 440 ball counterpart was used as an example in this study, any solid material with different shapes and surface finish can be applied using custom fixtures to simulate the actual application situation.

RESULTS & DISCUSSION

The Textured Belt and Smooth Belt have a surface roughness Ra of 33.5 and 8.7 um, respectively, according to the analyzed surface profiles taken with a NANOVEA 3D Non-Contact Optical profiler. The COF and wear rate of the two tested belts were measured at 10 N and 100 N, respectively, to compare the wear behavior of the belts at different loads.

FIGURE 1 shows the evolution of COF of the belts during the wear tests. The belts with different textures exhibit substantially different wear behaviors. It is interesting that after the run-in period during which the COF progressively increases, the Textured Belt reaches a lower COF of ~0.5 in both the tests conducted using loads of 10 N and 100 N. In comparison, the Smooth Belt tested under the load of 10 N exhibits a significantly higher COF of~ 1.4 when the COF gets stable and maintains above this value for the rest of the test. The Smooth Belt tested under the load of 100 N rapidly was worn out by the steel 440 ball and formed a large wear track. The test was therefore stopped at 220 revolutions.

FIGURE 1: Evolution of COF of the belts at different loads.

FIGURE 2 compares the 3D wear track images after the tests at 100 N. The NANOVEA 3D non-contact profilometer offers a tool to analyze the detailed morphology of the wear tracks, providing more insight in fundamental understanding of wear mechanism.

TABLE 1: Result of wear track analysis.

FIGURE 2: 3D view of the two belts
after the tests at 100 N.

The 3D wear track profile allows direct and accurate determination of the wear track volume calculated by the advanced analysis software as shown in TABLE 1. In a wear test for 220 revolutions, the Smooth Belt has a much larger and deeper wear track with a volume of 75.7 mm3, compared to a wear volume of 14.0 mm3 for the Textured Belt after a 600-revolution wear test. The significantly higher friction of the Smooth Belt against the steel ball leads to a 15 fold higher wear rate compared to the Textured Belt.

Such a drastic difference of COF between the Textured Belt and Smooth Belt is possibly related to the size of the contact area between the belt and the steel ball, which also leads to their different wear performance. FIGURE 3 shows the wear tracks of the two belts under the optical microscope. The wear track examination is in agreement with the observation on COF evolution: The Textured Belt, which maintains a low COF of ~0.5, exhibits no sign of wear after the wear test under a load of 10 N. The Smooth Belt shows a small wear track at 10 N. The wear tests carried out at 100 N create substantially larger wear tracks on both the Textured and Smooth Belts, and the wear rate will be calculated using 3D profiles as will be discussed in the following paragraph.

FIGURE 3: Wear tracks under optical microscope.

CONCLUSION

In this study, we showcased the capacity of the NANOVEA T2000 Tribometer in evaluating the coefficient of friction and wear rate of belts in a well-controlled and quantitative manner. The surface texture plays a critical role in the friction and wear resistance of the belts during their service performance. The textured belt exhibits a stable coefficient of friction of ~0.5 and possesses a long lifetime, which results in reduced time and cost on tool repairing or replacement. In comparison, the excessive friction of the smooth belt against the steel ball rapidly wears the belt. Further, the loading on the belt is a vital factor of its service lifetime. Overload creates very high friction, leading to accelerated wear to the belt.

The NANOVEA T2000 Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribocorrosion modules available in one pre-integrated system. NANOVEA’s unmatched range is an ideal solution for determining the full range of tribological properties of thin or thick, soft or hard coatings, films and substrates.

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