THE STRUCTURE OF NICRALY METAL POWDERS PLASMA-SPRAYED AND CAPTURED INWATER

The effect of plasma beam on the structure of NiCrAlY powders can be a possible source of structural inhomogeneities in plasma spray coating s. Results of structural studies performed with light microscopy, SEM, TEM, and EDX on NiCrAlY metallic powders plasma sprayed and captured in water are presented in this paper. The internal structure was found to consist of a mixture of phases including gamma, gamma', beta-NiAl and martensitic NiAl. Y is bound in the Ni5Y yttride localized in the grain boundary regions. Spherical caps containing O Al, Y, and Cr are formed at the surface of powders. The depletion of bulk powders of Al due to surface oxide formation was found to be the cause of a slight d ecrease of microhardness of plasma sprayed powder.