Verification of Dominant Factors for Splatting and Solidification of Plasma Sprayd Particles.

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The dominant factors for splatting and solidification of the plasma sprayd particles impinging on the flat substrate surface were systematically investigated by spraying the several metal powder materials on the AISI304 stainless steel substrate.The results obtained are summarized as follows :1)In the splatting of Ni, Cr, Cu, Fe and Mo powder on stainless steel substrate, typical splashing at the substrate temperature of 300K and a drastic fraction change of the splat pattern, from the form with splashing to the one without splashing with the substrate temperature, were observed. On the other hand, those were not recognized in the case of Al, Ti and Zr. It seems that splatting strongly depends on thje powder material.2)From the observation result of the bottom surface of the splat and the comparison of the latent heats of the powder materials, initial rapid solidification of the splat just after the impingement seems to be one of the remarkable reasonsfor the splashing.3)It revealed that the surface tension of the powder material was one of the dominant factors for the splashing from the relation between surface tension and transition temperature of the powder.4)The initial solidification rates of the powder impinged were estimated by the simple splat and solidification model, and the incident of the splashing corresponded well to the relation between solidification rate and surface tension of the powder material.5)As for the intervals between solidification and flattenning, it seems that both occur simultaneously when the solidification tends to occur easier, while the flattenning occurs preferentially followed by the solidification when the solidification rate is lower.6)Particle's velocity is not suspected to be responsible for the transition behavior in the splat pattern of the sprayd particle, for the transition behavior of the splat pattern attendant to the substrate temperature increasing was observed in HVOF sprayd particles.