Metallographic evaluation of the thermal history and velocity of powders during plasma spraying

Plasma-sprayed coatings are used in a wide range of engineering applications to combat oxidation, corrosion and wear. The plasma spraying process is ideally suited for refractory materials, but there are a number of process variables that need be controlled to obtain dense coatings. In spite of the considerable progress made in the theoretical understanding of this complex process, there is a need for a simple method to evaluate the interaction between the plasma flame and the powder particles that fonn the coatings. As reported in the literature, this involves metallographic observation of the powders collected from the plasma. In this paper, the results of such a study are presented. It is shown that this method is effective in detennining the extent of melting and the relative velocity of both metallic and ceramic powders.