WEAR OF TI-SI-N COATED CERAMIC CUTTING INSERTS

Multicomponent Ti-Si-N films with a very high hardness which were reported recently have a possible application for wear resistant coatings, especially for cutting inserts. This study performs the cutting test for a silicon nitride based ceramic insert coated with Ti-Si-N using a radio frequency-plasma enhanced chemical vapour deposition method with TiCl4, SiH4 and N-2 as feed stocks. The wear behaviour of coated specimens was evaluated under the selected cutting conditions. The influence of microstructure of the deposited film on wear properties was investigated. Evidence of reduction in crater wear was observed for the Ti-Si-N film deposited at a low SiH4, to TiCl4, flow ratio corresponding to the maximum hardness and finest microstructure obtained in this study. Attrition wear of the Ti-Si-N film was observed on the rake face whilst spalling appeared on the flank face. It is suggested that a ''solution strengthening'' of Si in the fine grain Ti-Si-N film deposited at a lower SiH4 to TiCl4 flow ratio promotes the hardness and reduces the friction at the chip-insert interface so that subsequent rake wear improvement can be obtained. However, the adhesion between film and substrate should be improved further.