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Category: Mechanical Testing

 

PTFE Coating Wear Test

PTFE COATING WEAR TEST

USING TRIBOMETER AND MECHANICAL TESTER

Prepared by

DUANJIE LI, PhD

INTRODUCTION

Polytetrafluoroethylene (PTFE), commonly known as Teflon, is a polymer with an exceptionally low coefficient of friction (COF) and excellent wear resistance, depending on the applied loads. PTFE exhibits superior chemical inertness, high melting point of 327°C (620°F), and maintains high strength, toughness, and self-lubrication at low temperatures. The exceptional wear resistance of  PTFE coatings makes them highly sought-after in a wide range of industrial applications, such as automotive, aerospace, medical, and, notably, cookware.

IMPORTANCE OF QUANTITATIVE EVALUATION OF PTFE COATINGS

The combination of a super low coefficient of friction (COF), excellent wear resistance, and exceptional chemical inert- ness at high temperatures makes PTFE an ideal choice for non-stick pan coatings. To further enhance its mechanical processes during R&D, as well as ensure optimal control over malfunction prevention and safety measures in the Quality Control process, it is crucial to have a reliable technique for quantity evaluating the tribomechanical processes of PTFE coatings. Precise control over surface friction, wear, and adhesion of the coatings is essential to ensure their intended performance.

MEASUREMENT OBJECTIVE

In this application, the wear process of a PTFE coating for a non-stick pan is simulated using NANOVEA Tribometer in linear reciprocating mode.

NANOVEA T50

Compact Free Weight Tribometer

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In addition, the NANOVEA Mechanical Tester was used to perform a micro scratch adhesion test to determine the critical load of the PTFE coating adhesion failure.

NANOVEA PB1000

Large Platform Mechanical Tester

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TEST PROCEDURE

WEAR TEST

LINEAR RECIPROCATING WEAR USING A TRIBOMETER

The tribological behavior of the PTFE coating sample, including the coefficient of friction (COF) and wear resistance, was evaluated using the NANOVEA Tribometer in linear reciprocating mode. A Stainless Steel 440 ball tip with a diameter of 3 mm (Grade 100) was used against the coating. The COF was continuously monitored during the PTFE coating wear test.

 

The wear rate, K, was calculated using the formula K=V/(F×s)=A/(F×n), where V represents 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 strokes. The wear track profiles were evaluated using the NANOVEA Optical Profilometer, and the wear track morphology was examined using an optical microscope.

WEAR TEST PARAMETERS

LOAD 30 N
TEST DURATION 5 min
SLIDING RATE 80 rpm
AMPLITUDE OF TRACK 8 mm
REVOLUTIONS 300
BALL DIAMETER 3 mm
BALL MATERIAL Stainless Steel 440
LUBRICANT None
ATMOSPHERE Air
TEMPERATURE 230C (RT)
HUMIDITY 43%

TEST PROCEDURE

SCRATCH TEST

MICRO SCRATCH ADHESION TEST USING MECHANICAL TESTER

The PTFE scratch adhesion measurement was conducted using the NANOVEA Mechanical Tester with a 1200 Rockwell C diamond stylus (200 μm radius) in the Micro Scratch Tester Mode.

 

To ensure the reproducibility of the results, three tests were performed under identical testing conditions.

SCRATCH TEST PARAMETERS

LOAD TYPE Progressive
INITIAL LOAD 0.01 mN
FINAL LOAD 20 mN
LOADING RATE 40 mN/min
SCRATCH LENGTH 3 mm
SCRATCHING SPEED, dx/dt 6.0 mm/min
INDENTER GEOMETRY 120o Rockwell C
INDENTER MATERIAL (tip) Diamond
INDENTER TIP RADIUS 200 μm

RESULTS & DISCUSSION

LINEAR RECIPROCATING WEAR USING A TRIBOMETER

The COF recorded in situ is shown in FIGURE 1. The test sample exhibited a COF of ~0.18 during the first 130 revolutions, due to the low stickiness of PTFE. However, there was a sudden increase in COF to ~1 once the coating broke through, revealing the substrate underneath. Following the linear reciprocating tests, the wear track profile was measured using the NANOVEA Non-Contact Optical Profilometer, as shown in FIGURE 2. From the data obtained, the corresponding wear rate was calculated to be ~2.78 × 10-3 mm3/Nm, while the depth of the wear track was determined to be 44.94 µm.

PTFE coating wear test setup on the NANOVEA T50 Tribometer.

FIGURE 1: Evolution of COF during the PTFE coating wear test.

FIGURE 2: Profile extraction of wear track PTFE.

PTFE Before breakthrough

Max COF 0.217
Min COF 0.125
Average COF 0.177

PTFE After breakthrough

Max COF 0.217
Min COF 0.125
Average COF 0.177

TABLE 1: COF before and after breakthrough during the wear test.

RESULTS & DISCUSSION

MICRO SCRATCH ADHESION TEST USING MECHANICAL TESTER

The adhesion of the PTFE coating to the substrate is measured using scratch tests with a 200 µm diamond stylus. The micrograph is shown in FIGURE 3 and FIGURE 4, Evolution of COF, and penetration depth in FIGURE 5. The PTFE coating scratch test results are summarized in TABLE 4. As the load on the diamond stylus increased, it progressively penetrated into the coating, resulting in an increase in the COF. When a load of ~8.5 N was reached, the breakthrough of the coating and exposure of the substrate occurred under high pressure, leading to a high COF of ~0.3. The low St Dev shown in TABLE 2 demonstrates the repeatability of the PTFE coating scratch test conducted using the NANOVEA Mechanical Tester.

FIGURE 3: Micrograph of the full scratch on PTFE (10X).

FIGURE 4: Micrograph of the full scratch on PTFE (10X).

FIGURE 5: Friction graph showing the line of the critical point of failure for PTFE.

Scratch Point of Failure [N] Frictional Force [N] COF
1 0.335 0.124 0.285
2 0.337 0.207 0.310
3 0.380 0.229 0.295
Average 8.52 2.47 0.297
St dev 0.17 0.16 0.012

TABLE 2: Summary of Critical Load, Frictional Force, and COF during the scratch test.

CONCLUSION

In this study, we conducted a simulation of the wear process of a PTFE coating for non-stick pans using the NANOVEA T50 Tribometer in linear reciprocating mode. The PTFE coating exhibited a low COF of ~0.18 the coating experienced a breakthrough at around 130 revolutions. The quantitative evaluation of the PTFE coating adhesion to the metal substrate was performed using the NANOVEA Mechanical Tester which determined the critical load of the coating adhesion failure to be ~8.5 N in this test.

 

The NANOVEA Tribometers offer precise and repeatable wear and friction testing capabilities using ISO and ASTM-compliant rotary and linear modes. They provide optional modules for high-temperature wear, lubrication, and tribocorrosion, all integrated into a single system. This versatility allows users to simulate real-world application environments more accurately and gain a beer understanding of the wear mechanisms and tribological properties of different materials.

 

The NANOVEA Mechanical Testers offer Nano, Micro, and Macro modules, each of which includes ISO and ASTM compliant indentation, scratch, and wear testing modes, providing the widest and most user-friendly range of testing capabilities available in a single system.

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Dynamic Mechanical Analysis of Cork Using Nanoindentation

DYNAMIC MECHANICAL ANALYSIS

OF CORK USING NANOINDENTATION

Prepared by

FRANK LIU

INTRODUCTION

Dynamic Mechanical Analysis (DMA) is a powerful technique used to investigate the mechanical properties of materials. In this application, we focus on the analysis of cork, a widely used material in wine sealing and aging processes. Cork, obtained from the bark of the Quercus suber oak tree, exhibits distinct cellular structures that provide mechanical properties resembling synthetic polymers. In one axis, the cork has honeycomb structure. The two other axes are structured in multiple rectangular-like prisms. This gives cork different mechanical properties depending on the orientation being tested.

IMPORTANCE OF DYNAMIC MECHANICAL ANALYSIS (DMA) TESTING IN ASSESSING CORK MECHANICAL PROPERTIES

The quality of corks greatly relies on their mechanical and physical properties, which are crucial for their effectiveness in wine sealing. Key factors determining cork quality include flexibility, insulation, resilience, and impermeability to gas and liquids. By utilizing dynamic mechanical analysis (DMA) testing, we can quantitatively assess the flexibility and resilience properties of corks, providing a reliable method for evaluation.

The NANOVEA PB1000 Mechanical Tester in the Nanoindentation mode enables the characterization of these properties, specifically Young’s modulus, storage modulus, loss modulus, and tan delta (tan (δ)). DMA testing also allows for the collection of valuable data on phase shift, hardness, stress, and strain of the cork material. Through these comprehensive analyses, we gain deeper insights into the mechanical behavior of corks and their suitability for wine sealing applications.

MEASUREMENT OBJECTIVE

In this study, perform dynamic mechanical analysis (DMA) on four cork stoppers using the NANOVEA PB1000 Mechanical Tester in the Nanoindentation mode. The quality of the cork stoppers is labeled as: 1 – Flor, 2 – First, 3 – Colmated, 4 – Synthetic rubber. DMA indentation tests were conducted in both the axial and radial directions for each cork stopper. By analyzing the mechanical response of the cork stoppers, we aimed to gain insights into their dynamic behavior and evaluate their performance under different orientations.

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PB1000

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TEST PARAMETERS

MAX FORCE75 mN
LOADING RATE150 mN/min
UNLOADING RATE150 mN/min
AMPLITUDE5 mN
FREQUENCY1 Hz
CREEP60 s

indenter type

Ball

51200 Steel

3 mm Diameter

RESULTS

In the tables and graphs below, the Young’s modulus, storage modulus, loss modulus, and tan delta are compared between each sample and orientation.

Young’s modulus: Stiffness; high values indicate stiff, low values indicate flexible.

Storage modulus: Elastic response; energy stored in the material.

Loss modulus: Viscous response; energy lost due to heat.

Tan (δ): Dampening; high values indicate more dampening.

AXIAL ORIENTATION

StopperYOUNG’S MODULUSSTORAGE MODULUSLOSS MODULUSTAN
#(MPa)(MPa)(MPa)(δ)
122.567522.272093.6249470.162964
218.5466418.271533.1623490.17409
323.7538123.472673.6178190.154592
423.697223.580642.3470080.099539



RADIAL ORIENTATION

StopperYOUNG’S MODULUSSTORAGE MODULUSLOSS MODULUSTAN
#(MPa)(MPa)(MPa)(δ)
124.7886324.565423.3082240.134865
226.6661426.317394.2862160.163006
344.0786743.614266.3659790.146033
428.0475127.941482.4359780.087173

YOUNG’S MODULUS

STORAGE MODULUS

LOSS MODULUS

TAN DELTA

Between cork stoppers, the Young’s modulus is not very different when tested in the axial orientation. Only Stopper #2 and #3 showed an apparent difference in the Young’s modulus between the radial and axial direction. As a result, the storage modulus and loss modulus will also be higher in the radial direction than in the axial direction. Stopper #4 shows similar characteristics with the natural cork stoppers, except in the loss modulus. This is quite interesting since it means the natural corks has a more viscous property than the synthetic rubber material.

CONCLUSION

The NANOVEA Mechanical Tester in the Nano Scratch Tester mode allows 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 to obtain corrected depth during the scratch and also to measure 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 technique of the instrument which can help manufacturers improved the quality of their hard coat/paint and study weathering effects.

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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

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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
Conical Indenter 90° Cone 2 µm tip radius

indenter type

Conical

Diamond 90° Cone

2 µm tip radius

Conical Indenter 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.

nano scratch critical failure initial damage

CRITICAL FAILURE:

COMPLETE DAMAGE

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

nano scratch critical failure complete damage

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
Micrograph of Full Scratch from nano scratch test(1000x magnification).

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

Micrograph of Initial Damage from nano scratch test (1000x magnification)

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

Micrograph of Complete Damage from nano scratch test (1000x magnification).

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

Linear Nano Scratch Test Friction Force and Coefficient of Friction

FIGURE 5: Friction Force and Coefficient of Friction.

Linear Nano Scratch Surface Profile

FIGURE 6: Surface Profile.

Linear Nano Scratch Test True Depth and Residual Depth

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.

NOW, LET'S TALK ABOUT YOUR APPLICATION

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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.

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T50

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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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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.

Compact Pneumatic Tribometer T100
NANOVEA T100

The Compact Pneumatic Tribometer

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NANOVEA PB1000

The Large Platform Mechanical Tester

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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 TYPEProgressive
INITIAL LOAD0.01 mN
FINAL LOAD5 N / 35 N
LOADING RATE10 / 70 N/min
SCRATCH LENGTH3 mm
SCRATCHING SPEED, dx/dt6.0 mm/min
INDENTER GEOMETRY120º cone
INDENTER MATERIAL (tip)Diamond
INDENTER TIP RADIUS200 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

LEARN MORE
nanoindenter and scratch tester 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)HSp (GPa)
Al6061174±110.84
Cu110220±10.52
SS30489±53.20

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

LEARN MORE
nanoindenter and scratch tester 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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Mechanical Properties of Hydrogel

MECHANICAL PROPERTIES OF HYDROGEL

USING NANOINDENTATION

Prepared by

DUANJIE LI, PhD & JORGE RAMIREZ

INTRODUCTION

Hydrogel is known for its super absorbency of water allowing for a close resemblance in flexibility as natural tissues. This resemblance has made hydrogel a common choice not only in biomaterials, but also in electronics, environment and consumer good applications such as contact lens. Each unique application requires specific hydrogel mechanical properties.

IMPORTANCE OF NANOINDENTATION FOR HYDROGEL

Hydrogels create unique challenges for Nanoindentation such as test parameters selection and sample preparation. Many nanoindentation systems have major limitations since they were not originally designed for such soft materials. Some of the nanoindentation systems use a coil/magnet assembly to apply force on the sample. There is no actual force measurement, leading to inaccurate and non-linear loading when testing soft materials. Determining the point of contact is extremely difficult as the depth is the only parameter actually being measured. It is almost impossible to observe the change of slope in the Depth vs Time plot during the period when the indenter tip is approaching the hydrogel material.

In order to overcome the limitations of these systems, the nano module of the NANOVEA Mechanical Tester measures the force feedback with an individual load cell to ensure high accuracy on all types of materials, soft or hard. The piezo-controlled displacement is extremely precise and fast. This allows unmatched measurement of viscoelastic properties by eliminating many theoretical assumptions that systems with a coil/magnet assembly and no force feedback must account for.

MEASUREMENT OBJECTIVE

In this application, the NANOVEA Mechanical Tester, in Nanoindentation mode, is used to study the hardness, elastic modulus and creep of a hydrogel sample.

NANOVEA

PB1000

nanoindenter and scratch tester Nanovea PB1000
TEST CONDITIONS

A hydrogel sample placed on a glass slide was tested by nanoindentation technique using a NANOVEA Mechanical Tester. For this soft material a 3 mm diameter spherical tip was used. The load linearly increased from 0.06 to 10 mN during the loading period. The creep was then measured by the change of indentation depth at the maximum load of 10 mN for 70 seconds.

APPROACH SPEED: 100 μm/min

CONTACT LOAD
0.06 mN
MAX LOAD
10 mN
LOADING RATE

20 mN/min

CREEP
70 s
RESULTS & DISCUSSION

The evolution of the load and depth as a function of time is shown in FUGURE 1. It can be observed that on the plot of the Depth vs Time, it is very difficult to determine the point of the change of slope at the beginning of the loading period, which usually works as an indication where the indenter starts to contact the soft material. However, the plot of the Load vs Time shows the peculiar behavior of the hydrogel under an applied load. As the hydrogel begins to get in touch with the ball indenter, the hydrogel pulls the ball indenter due to its surface tension, which tends to decrease the surface area. This behavior leads to the negative measured load at the beginning of the loading stage. The load progressively increases as the indenter sinks into the hydrogel, and it is then controlled to be constant at the maximum load of 10 mN for 70 seconds to study the creep behavior of the hydrogel.

FIGURE 1: Evolution of the load and depth as a function of Time.

The plot of the Creep Depth vs Time is shown in FIGURE 2, and the Load vs. Displacement plot of the nanoindentation test is shown in FIGURE 3. The hydrogel in this study possesses a hardness of 16.9 KPa and a Young’s modulus of 160.2 KPa, as calculated based on the load displacement curve using the Oliver-Pharr method.

Creep is an important factor for the study of a hydrogel’s mechanical properties. The close-loop feedback control between piezo and ultrasensitive load cell ensures a true constant loading during the creep time at the maximum load. As shown in FIGURE 2, the hydrogel subsides ~42 μm as a result of creep in 70 seconds under the 10 mN maximum load applied by the 3 mm ball tip.

FIGURE 2: Creeping at a max load of 10 mN for 70 seconds.

FIGURE 3: The Load vs. Displacement plot of the hydrogel.

CONCLUSION

In this study, we showcased that the NANOVEA Mechanical Tester, in Nanoindentation mode, provides a precise and repeatable measurement of a hydrogel’s mechanical properties including hardness, Young’s modulus and creep. The large 3 mm ball tip ensures proper contact against the hydrogel surface. The high precision motorized sample stage allows for accurate positioning of the flat face of the hydrogel sample under the ball tip. The hydrogel in this study exhibits a hardness of 16.9 KPa and a Young’s modulus of 160.2 KPa. The creep depth is ~42 μm under a 10 mN load for 70 seconds.

NANOVEA Mechanical Testers provide unmatched multi-function Nano and Micro modules on a single platform. Both modules include a scratch tester, hardness tester and a wear tester mode, offering the widest and the most user friendly range of testing available on a single
system.

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Adhesion Properties of Gold Coating on Quartz Crystal Substrate
 

Adhesion Properties of Gold Coating

on Quartz Crystal Substrate

Prepared by

DUANJIE LI, PhD

INTRODUCTION

The Quartz Crystal Microbalance (QCM) is an extremely sensitive mass sensor capable of making precise measurements of small mass in the nanogram range. QCM measures the mass change on the surface through detecting variations in resonance frequency of the quartz crystal with two electrodes affixed to each side of the plate. The capacity of measuring extreme small weight makes it a key component in a variety of research and industrial instruments to detect and monitor the variation of mass, adsorption, density, and corrosion, etc.

IMPORTANCE OF SCRATCH TEST FOR QCM

As an extremely accurate device, the QCM measures the mass change down to 0.1 nanogram. Any mass loss or delamination of the electrodes on the quartz plate will be detected by the quartz crystal and cause significant measurement errors. As a result, the intrinsic quality of the electrode coating and the interfacial integrity of the coating/substrate system play an essential role in performing accurate and repeatable mass measurement. The Micro scratch test is a widely used comparative measurement to evaluate the relative cohesion or adhesion properties of coatings based on comparison of the critical loads at which failures appear. It is a superior tool for reliable quality control of QCMs.

MEASUREMENT OBJECTIVE

In this application, the NANOVEA Mechanical Tester, in Micro Scratch Mode, is used to evaluate the cohesive & adhesive strength of the gold coating on the quartz substrate of a QCM sample. We would like to showcase the capacity of the NANOVEA Mechanical Tester in performing micro scratch tests on a delicate sample with high precision and repeatability.

NANOVEA

PB1000

nanoindenter and scratch tester Nanovea PB1000
TEST CONDITIONS

The NANOVEA PB1000 Mechanical Tester was used to perform the micro scratch tests on a QCM sample using the test parameters summarized below. Three scratches were performed to ensure reproducibility of the results.

LOAD TYPE: Progressive

INITIAL LOAD

0.01 N

FINAL LOAD

30 N

ATMOSPHERE: Air 24°C

SLIDING SPEED

2 mm/min

SLIDING DISTANCE

2 mm

RESULTS & DISCUSSION

The full micro scratch track on the QCM sample is shown in FIGURE 1. The failure behaviors at different critical loads are displayed in FIGURE 2, where critical load, LC1 is defined as the load at which the first sign of adhesive failure occurs in the scratch track, LC2 is the load after which repetitive adhesive failures take place, and LC3 is the load at which the coating is completely removed from the substrate. It can be observed that little chipping takes place at LC1 of 11.15 N, the first sign of coating failure. 

As the normal load continues to increase during the micro scratch test, repetitive adhesive failures occur after LC2 of 16.29 N. When LC3 of 19.09 N is reached, the coating completely delaminates from the quartz substrate. Such critical loads can be used to quantitatively compare the cohesive and adhesive strength of the coating and select the best candidate for targeted applications.

FIGURE 1: Full micro scratch track on the QCM sample.

FIGURE 2: Micro scratch track at different critical loads.

FIGURE 3 plots the evolution of friction coefficient and depth that may provide more insight in the progression of coating failures during the micro scratch test.

FIGURE 3: Evolution of COF and Depth during the micro scratch test.

CONCLUSION

In this study, we showcased that the NANOVEA Mechanical Tester performs reliable and accurate micro scratch tests on a QCM sample. By applying linearly increased loads in a controlled and closely monitored fashion, the scratch measurement allows users to identify the critical load at which typical cohesive and adhesive coating failure occurs. It provides a superior tool to quantitatively evaluate and compare the intrinsic quality of the coating and the interfacial integrity of the coating/substrate system for QCM.

The Nano, Micro or Macro modules of the 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.

In addition, an optional 3D non-contact profiler and AFM module are available for high resolution 3D imaging of indentation, scratch and wear track in addition to other surface measurements, such as roughness and warpage.

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The World’s Leading Micro Mechanical Tester
 

NOW THE WORLD'S LEADING

MICRO MECHANICAL TESTING

Prepared by

PIERRE LEROUX & DUANJIE LI, PhD

INTRODUCTION

Standard Vickers Micro Hardness Testers have usable load ranges from 10 to 2000 gram force (gf). Standard Vickers Macro Hardness Testers load from 1 to 50 Kgf. These instruments are not only very limited in range of loads but they are also inaccurate when dealing with rougher surfaces or low loads when indents become too small to be measured visually. These limitations are intrinsic to older technology and as a result, instrumented indentation is becoming the standard choice due to the higher accuracy and performance it brings.

With NANOVEA’s world leading micro mechanical testing systems, Vickers hardness is automatically calculated from depth versus load data with the widest load range on a single module ever available (0.3 grams to 2 Kg or 6 grams to 40 Kg). Because it measures hardness from depth versus load curves, the NANOVEA Micro Module can measure any type of materials including very elastic ones. It also can provide not only Vickers hardness but also accurate elastic modulus and creep data in addition to other types of test such as scratch adhesion testing, wear, fatigue testing, yield strength and fracture toughness for a complete range of quality control data.

NOW THE WORLD'S LEADING MICRO MECHANICAL TESTING

In this applications note, it will be explained how the Micro Module has been designed to offer the world’s leading instrumented indentation and scratch testing. The Micro Module’s wide range testing capability is ideal for many applications. For example, the load range allows for accurate hardness and elastic modulus measurements of thin hard coatings and can then apply much higher loads to measure the adhesion of these same coatings.

MEASUREMENT OBJECTIVE

The capacity of the Micro Module is showcased with the NANOVEA CB500 Mechanical Tester by
performing both indentation and scratch tests with superior precision and reliability using a wide load range from 0.03 to 200 N.

NANOVEA

CB500

LEARN MORE

TEST CONDITIONS

A series (3×4, 12 indents in total) of Microindentations were performed on a standard steel sample using a Vickers indenter. The load and depth were measured and recorded for the complete indentation test cycle. The indentations were performed to different maximum loads ranging from 0.03 N to 200 N (0.0031 to 20.4 kgf) to showcase the capacity of the micro module in performing accurate indentation tests at different loads. It is worth noting that an optional load cell of 20 N is also available to provide 10 times higher resolution for tests in the lower load range from 0.3 gf up to 2 kgf.

Two scratch tests were performed using the Micro Module with linearly increased load from 0.01 N to 200 N and from 0.01 N to 0.5 N, respectively, using conico-spherical diamond stylus with tip radius of 500 μm and 20 μm.

Twenty Microindentation tests were carried out on the steel standard sample at 4 N showcasing the superior repeatability of the Micro Module’s results that contrast the performance of conventional Vickers hardness testers.

*microindenter on the steel sample

TEST PARAMETERS

of the Indentation Mapping

MAPPING: 3 BY 4 INDENTS

RESULTS AND DISCUSSION

The new Micro Module has a unique combination of Z-motor, high-force load cell and a high precision capacitive depth sensor. The unique utilization of independent depth and load sensors ensures high accuracy under all conditions.

Conventional Vickers hardness tests use diamond square-based pyramid indenter tips that create square shaped indents. By measuring the average length of the diagonal, d, the Vickers hardness can be calculated.

In comparison, the instrumented indentation technique used by NANOVEA‘s Micro Module directly measures the mechanical properties from indentation load & displacement measurements. No visual observation of the indent is required. This eliminates user or computer image processing errors in determining the d values of the indentation. The high accuracy capacitor depth sensor with a very low noise level of 0.3 nm can accurately measure the depth of indents that are difficult or impossible to be measured visually under a microscope with traditional Vickers hardness testers.

In addition, the cantilever technique used by competitors applies the normal load on a cantilever beam by a spring, and this load is in turn applied on the indenter. Such a design has a flaw in case a high load is applied – the cantilever beam cannot provide sufficient structural stiffness, leading to deformation of the cantilever beam and in turn misalignment of the indenter. In comparison, the Micro Module applies the normal load via the Z-motor acting on the load cell and then the indenter for direct load application. All the elements are vertically aligned for maximum stiffness, ensuring repeatable and accurate indentation and scratch measurements in the full load range.

Close-up view of the new Micro Module

INDENTATION FROM 0.03 TO 200 N

The image of the indentation map is displayed in FIGURE 1. The distance between the two adjacent indents above 10 N is 0.5 mm, while the one at lower loads is 0.25 mm. The high-precision position control of the sample stage allows users to select the target location for mechanical properties mapping. Thanks to the excellent stiffness of the micro module due to the vertical alignment of its components, the Vickers indenter keeps a perfect vertical orientation as it penetrates into the steel sample under a load of up to 200 N (400 N optional). This creates impressions of a symmetric square shape on the sample surface at different loads.

The individual indentations at different loads under the microscope are displayed alongside of the two scratches as shown in FIGURE 2, to showcase the capacity of the new micro module in performing both indentation and scratch tests in a wide load range with a high precision. As shown in the Normal Load vs. Scratch Length plots, the normal load increases linearly as the conico-spherical diamond stylus slides on the steel sample surface. It creates a smooth straight scratch track of progressively increased width and depth.

FIGURE 1: Indentation Map

Two scratch tests were performed using the Micro Module with linearly increased load from 0.01 N to 200 N and from 0.01 N to 0.5 N, respectively, using conico-spherical diamond stylus with tip radius of 500 μm and 20 μm.

Twenty Microindentation tests were carried out on the steel standard sample at 4 N showcasing the superior repeatability of the Micro Module’s results that contrast the performance of conventional Vickers hardness testers.

A: INDENTATION AND SCRATCH UNDER THE MICROSCOPE (360X)

B: INDENTATION AND SCRATCH UNDER THE MICROSCOPE (3000X)

FIGURE 2: Load vs Displacement plots at different maximum loads.

The load-displacement curves during the indentation at different maximum loads are shown in FIGURE 3. The hardness and elastic modulus are summarized and compared in FIGURE 4. The steel sample exhibits a constant elastic modulus throughout the test load ranging from 0.03 to 200 N (possible range 0.003 to 400 N), resulting in an average value of ~211 GPa. The hardness exhibits a relatively constant value of ~6.5 GPa measured under a maximum load above 100 N. As the load decreases to a range of 2 to 10 N, an average hardness of ~9 GPa is measured.

FIGURE 3: Load vs Displacement plots at different maximum loads.

FIGURE 4: Hardness and Young’s modulus of the steel sample measured by different maximum loads.

INDENTATION FROM 0.03 TO 200 N

Twenty Microindentation tests were performed at 4N maximum load. The load-displacement curves are displayed in FIGURE 5 and the resulting Vickers hardness and Young’s modulus are shown in FIGURE 6.

FIGURE 5: Load-displacement curves for microindentation tests at 4 N.

FIGURE 6: Vickers hardness and Young’s Modulus for 20 microindentations at 4 N.

The load-displacement curves demonstrate the superior repeatability of the new Micro Module. The steel standard possesses a Vickers hardness of 842±11 HV measured by the new Micro Module, compared to 817±18 HV as measured using the conventional Vickers hardness tester. The small standard deviation of the hardness measurement ensures reliable and reproducible characterization of mechanical properties in the R&D and quality control of materials in both the industrial sector and academia research.

In addition, a Young’s Modulus of 208±5 GPa is calculated from the load-displacement curve, which is not available for conventional Vickers hardness tester due to the missing depth measurement during the indentation. As load decrease and the size of the indent decreases, the NANOVEA Micro Module advantages in terms of repeatability compare to Vickers Hardness Testers increase until it is no longer possible to measure the indent through visual inspection.

The advantage of measuring depth to calculate hardness also becomes evident when dealing with rougher or when samples are more difficult to observe under standard microscopes provided on Vickers Hardness Testers.

CONCLUSION

In this study, we have shown how the new world leading NANOVEA Micro Module (200 N range) performs unmatched reproducible and precise indentation and scratch measurements under a wide load range from 0.03 to 200 N (3 gf to 20.4 kgf). An optional lower range Micro Module can provide testing from 0.003 to 20 N (0.3 gf to 2 kgf). The unique vertical alignment of the Z-motor, high-force load cell and depth sensor ensures maximum structural stiffness during measurements. The indentations measured at different loads all possess a symmetric square shape on the sample surface. A straight scratch track of progressively increased width and depth is created in the scratch test of a 200 N maximum load.

The new Micro Module can be configured on the PB1000 (150 x 200 mm) or the CB500 (100 x 50 mm) mechanical base with a z motorization (50 mm range). Combined with a powerful camera system (position accuracy of 0.2 microns) the systems provide the best automation and mapping capabilities on the market. NANOVEA also offers a unique patented function (EP No. 30761530) which allows verification and calibration of Vickers indenters by performing a single indent across the full range of loads. In contrast, standard Vickers Hardness Testers can only provide calibration at one load.

Additionally, the NANOVEA software enables a user to measure the Vickers hardness via the traditional method of measuring the indent diagonals if needed (for ASTM E92 & E384). As shown, in this document, depth versus load hardness testing (ASTM E2546 and ISO 14577) performed by a NANOVEA Micro Module is precise and reproducible compared to Traditional Hardness Testers. Especially for samples that cannot be observed/measured with a microscope.

In conclusion, the higher accuracy and repeatability of the Micro Module design with its broad range of loads and tests, high automation and mapping options renders the traditional Vickers hardness testers obsolete. But likewise with scratch and micro scratch testers still currently offered but designed with flaws in the 1980’s.

The continuous development and improvement of this technology makes NANOVEA a world leader in micro mechanical testing.

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