Pure and Applied Chemistry

Abstract: Many kinds of both metallic and ceramic powder particles were plasma-sprayed onto the mirror-polished metallic substrate surface, and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature and ambient pressure. That is, the flattening behavior changed transitionally on that critical temperature and pressure range, respectively. We defined and introduced a transition temperature, T_t, and transition pressure, P_t, respectively, for those critical conditions. The role of the related factors (such as solidification of the bottom surface of the splat, desorption of adsorbates on the substrate surface and wetting at interface) on the transition behavior in the flattening was clarified from several points of views. The fact that the dependence both of transition temperature and transition pressure on the sprayed particle material had a similar tendency indicated that the wetting of the substrate by the molten particles seemed to be a domination in the flattening. A three-dimensional transition map by combining both transition temperature and transition pressure dependence was proposed as a controlling principle of the thermal spray process.