Role of substrate temperature on microstructure formation in plasma-sprayed splats

The flattening nature of the individual splat in thermal spraying is the fundamental process for the coating fabrication process, thus numerous studies have been conducted to understand the splat formation process in thermal spraying. In the present investigation, commercially available pure Cu particles with diameter of several tens of micrometers were thermally sprayed onto mirror polished AISI304 substrates held at various temperatures during the spraying. The top surface, bottom surface, and cross section morphologies of splats collected under designated conditions were observed in detail. According to the observation, different splat microstructures could be found varied with the substrate temperatures. In particular, a typical layer composed of fine grains could be found at splat–substrate interface when the substrate was held at high temperature, which has a close relation with the favorable wetting and enhanced heat transfer from molten droplet to substrate. This layer could induce the rapid decrease of droplet viscosity at the bottom surface and prevent the further spreading of the splat, which promoted the formation of disk-shaped splat.