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

通过在AISI304不锈钢表面喷涂几种金属粉末材料，系统地研究了等离子喷涂粒子撞击平板表面的飞溅和凝固的主导因素。结果表明：1)在不锈钢衬底上溅射镍、铬、铜、铁和钼粉末时，在300K的温度下观察到典型的飞溅现象，且飞溅形态发生了剧烈的变化，从有飞溅到无飞溅。另一方面，在Al、Ti和Zr的情况下，这些没有被识别。2)从飞溅底表面的观察结果和粉末材料的潜热比较来看，溅射后飞溅的初始快速凝固似乎是飞溅的重要原因之一。3)从粉末表面张力与转变温度的关系可以看出，粉末材料的表面张力是飞溅的主要因素之一。4)用简单的飞溅和凝固模型估算了被撞击的粉末的初始凝固速率。而飞溅的发生与粉末材料的凝固速度和表面张力之间的关系很好地对应。5)对于凝固和扁平化之间的间隔时间，当更容易发生凝固时，两者似乎同时发生，而当凝固速率较低时，扁平化优先发生在凝固之后。6)粒子的速度不是喷雾粒子飞溅模式转变行为的原因，因为在超音速火焰喷涂粒子中观察到了伴随着衬底温度升高的飞溅模式的转变行为。

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.