Metal Finishing Guide Book


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DLC coating HM HIT N/mm2 N/mm2 HV EIT/(1-vs^2) Gpa Mean 5903.9 12038.64 1137.65 Standard deviation 224.45 644.67 60.92 5.41 3.8 5.36 5.36 4.38 Variation% 123.4 Minimum 5671.9 11454.8 1082.5 118.6 Maximum 6198.1 12836.5 1213 130.3 Table 1: Hardness and elastic modulus measured by nanoindentation. The table shows mean value, standard deviation and coefficient of variation of five measurements. Figure 10: The graph shows the depth-dependent profile of the Martens Hardness of the DLC coating. ing a load though a sharp indenter and measuring the residual imprint under a microscope. However, this is almost impossible due to the elastic nature and dark color of the DLC coating. As these coatings are only a few microns in thickness the nanoindentation tester should have high depth resolution to allow for shallow indents to be performed, thus preventing the substrate material from influencing the measurements. And because ceramics have higher stiffness, the instrument must have a rigid frame to eliminate instrument compliance and only deform the material being tested. In this example, the measurement results of a 3 μm thick DLC layer are shown. The values for indentation hardness (HIT), Martens Hardness (HM) and indentation modulus (EIT) for the coating is listed in Table 1. The converted Vickers hardness (HV) helps correlate these measurements with traditional microhardness testers. The graph in Figure 10 maps the measured Martens Hardness as a function of indentation depth. Minimal change in this measurement with increasing depth indicates that even at maximum load there is no influence from the under lying substrate. CONCLUSION Improving the surface mechanical properties of materials boosts performance and increases life cycle of products. New developments in coating and surface treatment technology has seen nanoindentation gain wider acceptance. Combination of ISO and ASTM standards for nanoindentation and availability of off-the-shelf options from different vendors has also contributed to adoption 456

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