Wear mechanisms of diamond-coated tools

Polycrystalline diamond films were synthesised on WC-Co hard metal tools by DC plasma-jet CVD. For machining abrasive materials the hard, wear resistant diamond films must be of good quality (roughness, homogeneity, crystallinity, structure) and show strong adhesion to the substrate. The wear behaviour of thin diamond films has been examined with abrasive particles in blast wear test and under ultrasonically-induced high frequency vibrations of a sonotrode in cavitation tests. The conditions of CVD diamond synthesis were varied with regards coating duration and process engineering. The influence of pre-treating the substrate surface for enhanced adhesion of the diamond film was also analysed. The microjets of the cavitation test react sensitively to coating defects considering the microstructure of the material. The failure mechanism (adhesive, cohesive) could be deduced from the worn surface. The blast wear test is less sensitive to coating microstructure, but the time of first coating failure as a quantitative wear criterion is helpful for improving the quality and adhesion of the diamond films. Thereby, the adaptation of synthesis conditions of diamond films is supported.