Microstructure effect on the high-temperature oxidation resistance of Ti-Si-N coating layers

The oxidation behaviors of Ti-Si-N coating layers were investigated in terms of Si content and their characteristic microstructures. The Ti-Si-N films were characterized as composites of fine TiN crystallites and amorphous Si3N4 phase. The continuity of amorphous Si3N4 phase, i.e., the degree of encapsulation of TiN crystallites by amorphous Si3N4 phase, was an important key factor governing the oxidation behavior of Ti-Si-N coating layers. In the case of Ti-Si-N coating layers containing 4 at.% Si, TiN crystallites were not fully surrounded by the amorphous Si3N4 phase due to the insufficient amount of Si3N4 and the relatively large TiN crystallites size. Hence, the Ti-Si-N coating layers,contained 4 at.% Si fast oxidized through TiN crystallites above 600degreesC. However, Ti-Si-N coating layers containing the Si content above 10at.% showed much improved oxidation resistance even above 800degreesC because it had the finer TiN crystallites, and these TiN crystallites were fully surrounded by amorphous Si3N4 phase. The oxidation rate dependence on the Si content, and in particular the microstructure of Ti-Si-N film as derived from Si content, was systematically studied in this work.