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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.

 HOLEPEAK
SURFACE1.01 mm214.0 mm2
VOLUME8.799e-5 mm323.27 mm3
MAX DEPTH/HEIGHT0.0276 mm0.6195 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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