Effects of surface conditions on the flattening behavior of plasma sprayed Cu splats

Thermally sprayed coatings are built-up by successive molten or semi molten droplets impinging onto the substrate. It is commonly admitted that the flattening behavior determines the interaction of splats with the substrate or previously deposited under-layer and hence governs the overall quality of the sprayed deposit. Therefore a great number of works have been devoted to explain the flattening behavior and the splashing mechanisms from different aspects, such as fluid dynamic, solidification behavior, surface wettability, and surface adsorbates/condensates.Based on our contemporary understanding, the influence factors on splat flattening behavior were briefly reviewed. The roles of the substrate adsorbates/condensates level and substrate temperature were clearly emphasized as well as the conditions of the impinging particles. The plasma sprayed copper splats were examined on different surface conditions in this preliminary study. It was confirmed that a favorable surface condition tends to suppress the splashing and to promote the occurrence of disc-shaped splat. Results indicated that the intensive splashing phenomenon is associated with the evaporation of surface absorbates/condensates. The substrate nature and the particle parameters also affect the splat-flattening behavior. The disc-shaped copper splat prepared on cold substrate has smaller flattening degree than that one obtained on preheated substrate.