1999 Volume 17 Issue 2 Pages 243-250
A freely falling experiment, in which a metal droplet fell freely and impinged on a flat substrate, was conducted as a simulation of the thermal spray process. The effect of substrate temperature on the flattening and solidification of the droplet was mainly investigated in this study.
The transition of the splat pattern was recognized in the experiment, that is, the splat morphology of Ni and Cu droplet on the room temperature substrate was splash-type, while that on the high temperature substrate was disk-type. The cross section microstructure of the splat on the room temperature substrate was composed of an isotropic coarse grain, while that on the high temperature substrate was quite fine columnar structure. As the mean interparticle spacing in the splat changed transitionally with the substrate temperature, the solidification rate in the splat on the high temperature substrate was higher than that on the room temperature substrate. The unique porous microstructure and flowing pattern were observed in the bottom surface of the splat on the room temperature substrate while the flat microstructure without pore was recognized in that on the high temperature substrate. The difference of the solidification rate between these two kinds of splats seems to be attributed to the interface microstructure between splat and substrate. From the results obtained in this study, it can be concluded that the quite rapid solidification occured at the interface between splat and substrate when the droplet impinged on the cold substrate surface.
