Effect of Substrate Temperature and Ambient Pressure on Heat Transfer at Interface Between Molten Droplet and Substrate Surface

Millimeter-sized molten Cu droplets were deposited on AISI304 substrate surface by free falling experiment. The roles of substrate temperature and ambient pressure on heat transfer at interface between molten droplet and substrate surface were systematically investigated. The splat characteristics were evaluated in detail. Temperature history of molten droplet was measured at splat-substrate interface. Cooling rate of the flattening droplet was calculated as well. Furthermore, the spreading behavior of molten droplet on substrate surface was captured by high speed camera. The heat transfer from splat to substrate was enhanced both by substrate heating and by ambient pressure reduction, which can be attributed to the good contact at splat bottom surface. The splats in free falling experiment showed similar changing tendency as thermal-sprayed particles. Consequently, substrate temperature and ambient pressure have an equivalent effect to contact condition at interface between droplet and substrate surface. Substrate heating and pressure reduction may enhance the wetting during splat flattening, and then affect the flattening and solidification behavior of the molten droplet.