Fabrication of silicon nitride thick coatings by reactive RF plasma spraying

Silicon nitride (Si3N4) is one of the attractive ceramics in respect of its excellent properties both in wear and thermal shock resistance. In this research, Si3N4 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 Si3N4 coatings. Hydrogen addition as a reactive plasma gas improved the nitridation significantly. Si3N4 content in the coatings could be controlled by changing N-2 and/or H, fraction in plasma gas. Hardness of the coatings obtained increased with increasing Si3N4 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.