Plasma sprayed (PS) ceramic coatings have found widespread commercial use, particularly for wear resistant surfaces. Understanding of the micromechanical basis of macroscopic weight loss through wear is very important for the development of improved coatings and better uses for existing coatings. This paper aims to elucidate the wear mechanisms that occur when a PS ceramic coating is in sliding contact with a harder asperity, using controlled scratch testing as a model abrasion test. It attempts to relate the scratch test results to the microstructural integrity, or cohesion, of the various coatings. Paper includes a German-language abstract.

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.