Alumina Coatings by Plasma Spraying of Monosize Sapphire Particles

In an effort to obtain a series of plasma-sprayed coatings of controlled microstructure, three monosized sapphire powders were deposited using an axial injection torch in which the plasma gas composition and nozzle diameter were the only parameters varied. The effect of these parameters on splat morphology, porosity, angular crack distribution, and hardness is reported. Uniform, dense microstructure with a hardness rivaling chromia coatings was achieved through a combination of tightly controlled processing conditions and the use of mono-disperse precursor powders.