Study of the Splat Microstructure and the Effects of Substrate Heating on the Splat Formation for Ni-Cr Particles Plasma Sprayed onto Stainless Steel Substrates

The plasma spraying process is still poorly understood in term of the processes by which the coating is built up, especially coating interactions with the substrate. This present study enhances this understanding by studying, through a range of electron microscopy techniques, single NiCr splats plasma sprayed onto stainless steel substrates, which were first exposed to different heat treatments. The microstructure of the splats, particularly the splat-substrate interface, was characterized, and the formation of the observed features is discussed. Evidence of localized substrate melting and inter-mixing with the splat material was found, showing metallurgical bonding. The structures observed were also correlated to the treatment of the substrate, demonstrating how such treatments can influence the properties of the fully deposited coating by modifying the splat formation process. Most notably, heating the substrate during spraying was found to significantly modify splat formation by reducing splashing and increasing the extent of substrate melting.