Recently, we have shown that the splat morphology of most metallic materials thermally sprayed strongly depend on the substrate temperature and usually the change occur drastically near the transition temperature; Tt. In the present study, theeffects of substrate material, powder material and PVD coating material on the flattening of the plasma sprayed ceramic particles were investigated.Commercially available several kinds of powders, that is, A1{sub}2O{sub}3, TiO{sub}2 and YSZ, were plasma sprayed and collected on the mirror polished substrate surface. The substrate materials are AISI304 stainless steel, brass and glass, and those wereheld at a designated temperature before spraying. To investigate the effect of wetting on the flattening of the particle, Au, Ti and Al coated substrates by PVD were also prepared.The splat morphology collected on the room temperature substrate was splash type. As the substrate temperature increased, the central solidification area of the splash splat gradually enlarged, and finally the splat morphology changed to the disk typeover Tt range. This transition is maybe caused by both the improvement of wettability at splat/substrate interface and suppression of rapid solidification with the substrate temperature increasing.The different transition behavior was observed on the common substrate material with each PVD coating. It is well known that the standard formation free energy of oxide can be closely related to the static wetting of melt material on the substrate. Ifthis relation can be applicable to the dynamic wetting like thermal sprayed particles on the substrate, it can be estimated from the results obtained that the better wetting promotes the occurence of the disk splat. The observation results of the bottomsurface microstructures of the splats supported well this hypothesis.Consequently, it was clarified that the wetting played an important role on the flattening behavior of the plasma sprayed ceramic particles.
展开▼
