Examination of Substrate Surface Melting-Induced Splashing During Splat Formation in Plasma Spraying

Abstract

Abstract Impacting of a molten droplet with melting point much higher than substrate results in melting of substrate around the impact area. The melting of the substrate surface to certain depth alters the flow direction of droplet fluid. The significant change of fluid flow direction leads to detaching of fluid from contact with the substrate. Consequently, splashing occurs during droplet spreading process. In the present study, Mo splats were formed on stainless steel substrate under different plasma spraying conditions. For comparison, Mo splats were also deposited on Mo surface. The substrate surface was polished prior to deposition. The powders used have a narrow particle size distribution. The results show that the morphology of splats depends significantly on the thermal interaction between the molten particle and the substrate. The splat observed was only a central part of an ideal disk-like complete splat. The typical pattern of Mo splats was the split type presenting a small split structure on stainless steel substrate surface. With Mo particles, the preheating of steel substrate has no effect on splat morphology. On the other hand, disk-like type Mo splat with a reduced diameter of a dimple-like structure at the central area of the splat was formed on Mo substrate and splashing can be suppressed through substrate preheating. Based on the experimental results, a surface-melting- induced splashing model was proposed to explain the formation mechanism of Mo splat on steel surface.