Optimization of Plasma Spray Processing Parameters for Deposition of Nanostructured Powders for Coating Formation

When nanostructured powder particles are used for thermal spray coatings, the retention of the original nanostructure that is engineered into the raw stock is a principal objective, along with production of some molten material in order to adhere the sprayed material to the surface being coated. Therefore, in contrast with spraying conventional powders, complete melting of the nanostructured raw stock is to be avoided. In this study, the melting and resolidification of sprayed material is correlated to a spray processing parameter that has been introduced in the literature by some of the spray processing practitioners. Using computer modeling, processing of zirconia agglomerates with plasma spraying has been simulated. Transition regions for the phase change response of the sprayed material to the thermal processing conditions are identified. The retained nanostructure content and liquid fraction of the sprayed material are correlated to particle diameters, injection velocities, as well as this thermal spray processing parameter. Finally, a novel method to produce desired coatings composed of partially molten material using a bimodal particle size distribution of the sprayed powder is suggested.