Splat Formation Mechanism in Thermal Spray Process According to Substrate Temperature and Ambient Pressure Change

Abstract

Abstract Aiming at clarifying the individual splat formation mechanism in thermal spray process, commercially available metallic powders were thermally sprayed onto AISI304 substrate surface. The splats changed from a distorted shape with splash to a disk-shaped splat in flattening after collision onto substrate surface, through substrate preheating and/or reducing the ambient pressure. Accordingly, both substrate temperature and ambient pressure have an equivalent effect on the shape transition. The observation on the bottom surface morphology of single splat indicated that the ring-shaped initial solidification might play an important role during splat formation process. As a simulation of the real thermal spray process, free falling experiment has been conducted. The thermal history of the free falling metal droplet onto AISI304 substrate indicated that the flattening pattern is decided so quicky just after collision onto solid surface, which is enough earlier to the finalization of the flattening.