Fabrication of Silicon Nitride Thick Coatings by Reactive RF Plasma Spraying

Abstract

Silicon nitride (Si 3 N 4 ) is one of the attractive ceramics in respect of its excellent properties both in wear and thermal shock resistance. In this research, Si 3 N 4 thick coatings were fabricated by reactive RF (Radio Frequency) plasma spray process, and a reactive plasma spraying, in which metal element reacts with surrounding active species in plasma, has been considered to be an useful way for the formation of non-oxide ceramics coatings. Spraying with Ar/N 2 mixed gas was not effective for the fabrication of Si 3 N 4 coatings. Hydrogen addition as a reactive plasma gas improved the nitridation significantly. Si 3 N 4 content in the coatings could he controlled by changing N 2 and/or H 2 fraction in plasma gas. Hardness of the coatings obtained increased with increasing Si 3 N 4 content in the coating. Nitriding reaction of Si in reactive RF plasma spraying was promoted in the liquid phase of Si after deposited onto the substrate.