Abstract
Thermal spray coatings are formed by successive molten droplets impinging onto a 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 number of works have been devoted to explain the splashing mechanisms and the flattening behavior from different aspects, such as fluid dynamics, solidification behavior, surface wettability or surface adsorbates/condensates. It was thus shown that surface conditions such as surface roughness, contaminants, adsorption, etc. play a very important role in controlling the splat flattening behavior. In this study, the role of the substrate condition as well as that of the impinging particle parameters are emphasized in the case of a copper deposit formed on a titanium base alloy and on a stainless steel substrates. The plasma sprayed copper splats were examined for different surface conditions. It was thus confirmed that favorable surface conditions tend to suppress splashing and to promote the occurrence of disc-shaped splats while the substrate nature and particle parameters also affect the splat flattening behavior. Results also indicated that disc-shaped copper splats prepared on a cold substrate have a smaller flattening degree than those obtained on a preheated substrate.
