On the measurement of hardness of super-hard coatings

The measurement of indentation hardness on super-hard nanocomposite coatings: nc-TiN/a-Si3N4 and nc-TiN/a-BN is investigated. Previously reported test methods and analysis techniques are reviewed and critically discussed. The hardness of two representative coatings measured by nanoindentation, direct AFM imaging, and also from finite element analysis are presented. Previously published data for ultra-hard coatings were re-analysed for comparison purposes. A sample of industrial diamond was also tested and results for modulus and hardness are reported. It is shown that the previously reported hardness values in the range 35–50 GPa for these types of coatings are supported, despite some areas of concern in the test methods used. Re-analysis of previously reported data for ultra-hard coatings yielded inconsistent results, while the modulus and hardness of industrial diamond were found to be reasonable for this material when calculated using the Oliver and Pharr method.