抄録
Plasma-sprayed coatings are deposited onto a substrate by the flattened splats of the molten metal and ceramic droplets. The quality of the formed deposit greatly depends on the individual flattened splats. This paper presents free-falling and splat-formation experiments in which the molten droplets of Sn, Pb, Cu and Fe were impinged on the cold substrate and solidified after the flattening process. To evaluate the contour of the flattened splats, the unevenness ratio was introduced and defined by the contour length of the flattened splat to the circumferential length of an equivalent regular circle having the same area as the flattened splat.This report presents that the fractal dimension is introduced to a new evaluating measure for the contour of flattened splats. The unevenness ratio and fractal dimension with respect to W, Re and We change in a bi-linear relation for the molten droplets approximately in the same size. In the region beyond kinked point, the splat periphery shows a splash-like contour due to the Rayleigh instability. We call this point the critical-unevenness ratio, -Re and- We numbers. These critical values change with the viscosity and surface tension of the molten metal.
