Wear Evaluation of Hard Metal Using Tribometer

Wear is related to the removal and deformation of material on a surface as a result of mechanical action of the opposite surface. Different types of wear, e.g. abrasion, friction and erosion, take place in virtually every industrial sector and create huge direct and consequential annual losses to the U.S. economy. A study carried out by ASM International (American Society for Metals) showed that wear imposes costs of ~0.75% of the GDP¹. As a result, tribology research is critical in improving production efficiency and application performance, as well as the conservation of material, energy and the environment.

In order to extend the lifetime of mechanical components and to cut the cost and time of part repair and replacement, surface engineering is carried out to harden the metal surface for wear protection while maintaining the toughness of the core metal. In particular, in this study, surface treatment on the test saw blades has formed a hard surface layer to enhance the wear resistance. Additionally, a low surface friction is favorable to reduce the interaction of the blade and the object to be cut, so as to reduce tool wear and improve cutting efficiency. Therefore, reliable evaluation of the wear performance of surface treated metals is desirable for R&D and quality control in the metal industry.

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The coefficient of friction, COF, and the wear resistance of three saw blades were evaluated by the NANOVEA Tribometer using the Linear Reciprocating Wear Module. An Al₂O₃ ball (6 mm diameter) was used as the counter material. The wear track was examined using the NANOVEA 3D non-contact profilometer after the tests. The test parameters are summarized in Table 1.

Please note that the Al₂O₃ ball as a counter material was used as an example in this study; any solid material with different shapes can be applied using a custom fixture to simulate the actual application situation.

The COF and wear rate of three surface hardened saw blades were measured using the Linear Reciprocating Wear Module. Fig. 2 shows that the three saw blades exhibit significantly different wear behaviors, as indicated by the evolution of COF during the tests. Sample A shows a low COF of ~0.1 at the beginning of the wear test, which slowly increases to a value of ~0.25 until 1600 revolutions. The COF drastically climbs to ~0.7 in the following 100 revolutions, and stays above this value for the rest of the test. Such a drastic change of COF is attributed to the penetration of the Al₂O₃ ball through the hardened surface and the exposure of the fresh metal underneath. In comparison, Sample B and Sample C exhibit such a significant change to high COF values after 900 and 80 revolutions, respectively, indicating their relatively poorer wear performance compared to Sample A.

Fig. 3 compares the 3D wear track images after the tests measured by the NANOVEA non-contact profilometer. The 3D wear track profile allows direct and accurate determination of the wear track volume calculated by the NANOVEA analysis software, and Table 2 summarizes the results of the wear track analysis. Fig. 4 shows the wear tracks of the three saw blades under the optical microscope. The wear track evaluation is in agreement with the observation of COF evolution: Sample A, which maintains the low COF for the longest period, exhibits the lowest wear volume of 0.13 mm³, compared to 0.23 and 0.32 mm³ for Samples B and C, respectively. The data shown here represents only a small portion of the calculations available in the analysis software.

The wear resistance of cutting tools, e.g. the saw blades in this study, is critical in their service performance. A hardened surface layer can significantly extend the lifetime of the cutting tools and reduce the time and cost of tool repair or replacement. In this study, we showcased the capacity of the NANOVEA Tribometer in evaluating the coefficient of friction and wear rate of surface hardened metals in a controlled and monitored manner.

This measurement allows users to quantitatively assess the tribological behaviors of the materials and select the best candidate for the targeted applications. COF serves as an important indicator of the failure of the protective surface layer or coating. The NANOVEA 3D non-contact profilometer enables precise wear volume measurement and offers a tool to analyze the detailed morphology of the wear tracks, providing more insight into the fundamental understanding of wear mechanisms.

NANOVEA Tribometers offer 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.

1. Davis, J. R., Surface Engineering for Corrosion and Wear Resistance, ASM International, 2001.