Micro- and nanostructured diamond films under wear charging in cavitation test

Polycrystalline diamond coatings have been deposited on WC–Co hardmetal tools by the hot filament chemical vapour deposition technology to get improved wear protection. The good adhesion at the interface coating/substrate was achieved by an optimised pre-treatment of the substrate surface. The wear behaviour of micro- and nanostructured diamond films was examined with ultrasonic equipment for cavitation charging. The influence of coating structure, roughness and thickness on the wear resistance was investigated. The micro-jets of the cavitation test react sensitively to coating defects and consider the micro- or nanoscale structure of the material. The failure mechanism could be deduced from the worn surfaces as cohesive in all cases. Because the cavitation erosion happens layer-by-layer, the nanocrystalline, smooth diamond films consisting of extremely thin nanolayers have a much better wear resistance than the microcrystalline, rough coatings with their multi-layer structure. Thus, the thin film system nanocrystalline diamond/hardmetal substrate shows an outstanding performance and extremely long lifetime in wear applications, if there are no coating defects. The extraordinary wear resistance for thin, nanocrystalline diamond films with optimised adhesion and layer strength could be further enhanced by producing thicker films.