Formation of Plasma-Sprayed Oxide Coatings

摘要

This paper is an overview of the presentknowledge of the phenomena that affect the formation andquality of plasma-sprayed zirconia and alumina coatings.The characteristics of particles in flight and theircondition at the point of impact, the flattening of themolten particles, the cooling of the resulting splatsafter impact, and the formation of coating by theaccumulation of successive splats are discussed, alongwith the laboratory and industrial instrumentationsthat have been developed to study these phenomena. Athreshold substrate temperature has been identifiedabove which the splats on smooth surfaces (Ra<0.1 #mu#m)have a perfect disk shape and excellent contact with theunderlying material. The formation of the coating andits adhesion/cohesion values depend on residualstresses which are related to the initial condition ofthe surface to be coated, the preheating temperature andthe thickness of material deposited in successive passesof the plasma torch over the coated surface.