The Microstructure of Functionally Gradient Material Made by Plasma Spraying

Abstract

This study was aimed at development of a fabrication process of Functionally Gradient Material (FGM), consisting of NiCr and YSZ, made by using Low Pressure Plasma Spraying. Our research showed that the density of coatings largely depended on the pressure, substrate position and particle size during spraying. And studies were carried out on the microstructure of FGM compared with NiCr and YSZ monotonunous coatings. In the case of a NiCr monotonous coating and YSZ monotonous coating, the microstructures of particles were of a columnear type. The direction of grain growth was perpendicular to the surface of the coating. On the other hand, in the case of FGM, the microstructure of NiCr was of an equiaxed type. In this case, the deposited and solidified NiCr particles were considered to be remelted again by the molten YSZ particles, which impinged on these NiCr particles and to solidify at a relatively slow rate. Additionally, investigation of the interface between Cu substrate and coating, and also between particles was carried out in an atomic scale. The results showed that the interface was formed by either a thin oxide amorpous composite layer or a coherently connected crystal plane boundary.