Coating materials of TiN, Ti–Al–N, and Ti–Si–N by plasma-enhanced chemical vapor deposition for mechanical applications

TiN-based hard-coating layers were deposited on steel substrate at 500 °C by a plasma-enhanced chemical vapor deposition (PECVD) technique. In this work, comparative studies on micro-hardness, microstructure, and oxidation behavior among TiN, Ti–Al–N and Ti–Si–N coating layers by PECVD were conducted. Even a small amount of Al or Si addition to TiN had large effects on the improvement in both micro-hardness and oxidation resistance of TiN film. The large increase of micro-hardness for Ti–Al–N and Ti–Si–N, compared with TiN, was caused by microstructural modification of TiN with the addition of Al or Si, e.g., to grain-size refinement and the mixed crystallographic orientation of grains. While TiN film started to oxidize from 500 °C, Ti–Al–N and Ti–Si–N coating layers showed much improved oxidation resistance up to 700 °C. Amorphous aluminum oxide and silicon oxide phases formed at the initial oxidation stage for Ti–Al–N and Ti–Si–N, respectively, played a role in retarding further oxidation. On comparison of Ti–Al–N and Ti–Si–N, Ti–Si–N coating layer showed better merit in mechanical property at moderate temperature, while Ti–Al–N had larger advantage in the resistant property against high temperature oxidation.