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 degreesC 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 degreesC, Ti-Al-N and Ti-Si-N coating layers showed much improved oxidation resistance up to 700 degreesC. 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 temperatureoxidation. (C) 2002 Elsevier Science B.V. All rights reserved.