Splat-Substrate Interactions in Plasma Sprayed Ni-Cr Powders on Polished Metal Substrates

This study has investigated the structural and chemical interactions between plasma sprayed Ni-Cr particles on 5052 Al and 304L stainless steel substrates as a function of the surface condition of the substrates. In the presented work, substrates were ground and polished to a surface roughness of ~5nm prior to plasma spray. Detailed microstructural characterization of the splat-substrate interface was performed by atomic force microscopy, SEM, focused ion beam microscopy and TEM. In both materials a range of splat morphologies were exhibited. Cross-sectional analysis of each splat type was performed and a range of microstructural features, including the presence of oxides, voids and delamination was observed. TEM studies of the splat-substrate cross-sections show that melting of the substrate, together with chemical intermixing between the substrate and splat, occurred for the steel substrate, but not for the aluminum substrate. The observed structures were correlated to the heat flow occurring during splat solidification.