REMELTING PHENOMENA IN THE PROCESS OF SPLAT SOLIDIFICATION

A combined theoretical and experimental study is reported which investigates remelting phenomena during the splat cooling of two liquid-metal droplets impacting sequentially on a substrate. Under conditions of sufficiently high superheat it was proposed theoretically and demonstrated experimentally that an initial deposit is remelted by the subsequent impact of molten material. It is shown that the amount of superheat as well as the variation of thermophysical properties, particularly the latent heat and the melting temperature, influence the degree of remelting. Experimental findings supported to a certain extent the thee retical model assumptions that the splats could be represented by thin discs and that the heat transfer and solidification within the splat propagates in the axial direction only. However, the experiments showed that these assumptions are better suited for the central region of the splat. The occurrence of remelting often depended on the radial location for a given amount of superheat. For most part, the splat exhibited globular microstructure. Lamellar structures were observed near the top and the periphery of the splat, indicating slower cooling rates at these locations. The theoretical model constituted a good compromise between accuracy and simplicity and predicted the correct trends of the remelting phenomenon.