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Category: Scratch Testing | Scratch Hardness

 

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

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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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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

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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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A BETTER Look at Polycarbonate Lens

A BETTER Look at Polycarbonate Lens Learn more
 
Polycarbonate lenses are commonly used in many optical applications. Their high impact resistance, low weight, and cheap cost of high-volume production makes them more practical than traditional glass in various applications [1]. Some of these applications require safety (e.g. safety eyewear), complexity (e.g. Fresnel lens) or durability (e.g. traffic light lens) criteria that are difficult to meet without the use of plastics. Its ability to cheaply meet many requirements while maintaining sufficient optical qualities makes plastic lenses stand out in its field. Polycarbonate lenses also have limitations. The main concern for consumers is the ease at which they can be scratched. To compensate for this, extra processes can be carried out to apply an anti-scratch coating. Nanovea takes a look into some important properties of plastic lens by utilizing our three metrology instruments: Profilometer, Tribometer, and Mechanical Tester.   Click to Read More!
High Temperature Tribology

High Temperature Scratch Hardness Using Tribometer

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 high temperature scratch hardness is in need to ensure proper selection of the materials for high temperature applications.

High Temperature Scratch Hardness Using Tribometer

 

Scratch Hardness Measurement Using Tribometer

In this study, the Nanovea Tribometer is used to measure the scratch hardness of different metals. The
capacity of performing scratch hardness measurement with high precision and reproducibility makes
Nanovea Tribometer a more complete system for tribological and mechanical evaluations.

Scratch Hardness Measurement Using Tribometer

Mechanical & Tribological Properties of Carbon Fiber

Combined with the wear test by Tribometer and surface analysis by Optical 3D Profilometer, we
showcase the versatility and accuracy of the Nanovea instruments in testing composite materials
with directional mechanical properties.

Mechanical & Tribological Properties of Carbon Fiber

Micro Scratch Depth Measurement Using 3D Profilometry

In this application the Nanovea ST400 Profilometer is used for depth measurement of a row of micro scratches created using Nanovea’s Mechanical Tester in scratch mode. In seconds the Profilometer, with a single line pass in 2D mode, provides area and depth  measurement.

Depth Measurement of Micro Scratches Using 3D Profilometry

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