Fabrication of Silicon Nitride Coating by Reactive Plasma Spray using Ar, N2, and H2 Mixed Gas

In recent years, silicon nitride has received great interest for its excellent properties. Especially for high temperature applications and resistance of wear and corrosion, silicon nitride coating might contribute to the durability of various structural parts. However, fabrication of silicon nitride coating by conventional spraying techniques causes difficulties of its decomposition without a stable melting phase. In this research, the reactive Radio Frequency (RF) plasma spraying, which can fabricate nitride ceramic coatings, was used. Adding hydrogen as reactive plasma gas with argon and nitrogen improves nitridation significantly. Without hydrogen gas, we can't obtain the silicon nitride coating. The nitriding mechanism is that gaseous nitrogen diffuses to liquid silicon, which melts on the substrate, then Si3N4 coating forms. On an influence of hydrogen addition, we supposed that hydrogen removes an oxide layer on the silicon particles and/or improves thermal efficiency of plasma.