Experimental determination of the interfacial heat transfer during cooling and solidification of molten metal droplets impacting on a metallic substrate: Effect of roughness and superheat

The interfacial heat transfer between a solidifying molten metal and a metallic substrate is critical in many processes such as strip casting and spray deposition. As the molten metal cools down and solidifies, the interface undergoes a change from the initial liquid/solid contact to a solid/solid contact, leading to very dynamic variations in the rate of interfacial heat transfer. This article presents the results of an experimental study of the contact heat transfer when molten nickel or copper droplets are dropped on an inclined metallic substrate. The interfacial heat transfer coefficient, h, between the melt and the substrate is evaluated by matching model calculations with the top splat surface temperature history measured by a fast-response pyrometer. The results suggest that a high value of the interfacial heat transfer coefficient h (10⁴ to 3 × 10⁵ W/m² K) is achieved when the molten splat is in contact with the substrate, followed by a smaller value (<10⁴ W/m² K) during the later stages of solidification and the solid cooling phase. A parametric study was performed to investigate the effect on h of the metal/substrate materials combination, the melt superheat, and the substrate surface roughness, and some of the results are also presented.