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Evaluation of splat profile for droplet impingement

Surface and Coatings Technology
Publication Date
DOI: 10.1016/s0257-8972(99)00175-9
  • Droplet
  • Flattening
  • Free Fall
  • Molten Metal
  • Peripheral Profile
  • Unevenness Ratio


Abstract 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. The unevenness ratio can represent how the splats change their profile on their periphery, and it is influenced by the impinging velocity, W, as well as Re and We numbers. If we plot the unevenness ratio with respect to W, Re and We for the molten droplets in approximately the same size, a bi-linear relation was obtained. In the region beyond a corner (kinked) point, the splat periphery shows a splash-like contour due to the Rayleigh instability. We call this point the crtical-unevenness ratio — Re and — We numbers. These critical values change with the viscosity and surface tension of the molten metal.

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