Abstract
The peculiarities of plasma treatment of agglomerated YSZ powders as well as mechanically pretreated metal and metal alloy powder with the aim of their spheroidization and subsequent thermal spraying of produced HOSP powders are analyzed. Formation of splats from hollow droplets deserves a special attention for thermal spraying. In this case, immediately prior to particle – substrate collision, we have a droplet that consists of a liquid shell enclosing a gas cavity heated to a temperature close to the particle surface temperature. The paper presented includes the results of computer simulation and model experiments carried out under full control of pre-impact key physical parameters (KPPs): temperature Tp0, velocity up0, external diameter of droplet Dp0, thickness of its shell Δp0 , temperature of substrate Tb0, and its surface state. It was shown that formation of splats from hollow droplets proceeds in a manner more stable compared to the case of “dense” molten particles obtained from fused and crushed compacts, and this provides for a more perfect splat-substrate, splat-splat and coating-substrate interface. Advantages of hollow metal, metal alloy and metal oxide powders over corresponding dense powders for thermal spraying by the example of thermal barrier coatings are discussed. Since the splat formation process involving hollow droplets proceeds, following their high-velocity impact deformation on the base/substrate, in an explosive manner, this type of spraying can be referred as HOSP micro explosive thermal spraying.
