Influence of Substrate Temperature on Dynamic Wetting by Freely Fallen Droplet

Abstract

A free failing experiment has been conducted as a simulation of a thermal spray process to investigate the effect of substrate temperature on wetting at splat / substrate interface. A gold-coated substrate was prepared by ion sputtering to change the wetting conditions. The experiments were conducted both in atmospheric pressure nitrogen and under low-pressure condition.
The grain size in the cross-section microstructure of the splat obtained under low-pressure condition was quite small even on the room temperature substrate and the bottom surface microstructure was quite dense. It was found that the ambient gas has a physical restraint effect on the wetting by introducing the pores at interface. The grain size in the cross-section microstructure of the splat on gold-coated substrate was also small and the bottom surface microstructure was quite dense. It was recognized that both materials factor and temperature factor affect the wetting at interface with substrate temperature increasing. The transition phenomenon in the wetting with substrate temperature increasing was indicated to be due to materials factor induced wetting, such as a surface roughening by an oxidation of the substrate.