Feasibility of suspension spraying of yttria-stabilized zirconia with water-stabilized plasma torch

Thermal spraying of suspensions allows preparation of coatings from submicron-sized powders but demands a source of heat with a high enthalpy in order to provide an appropriate thermal treatment of the liquid feedstock during the in-flight stage so that the solvent may be evaporated, dispersed particles melted and accelerated towards the substrate to form a coating. Water-stabilized plasma (WSP) torch developed at the Institute of Plasma Physics AS CR, v.v.i. provides such a heat source with high enthalpy, high velocity of the plasma and, when compared to high-enthalpy gas-stabilized plasma (GSP) torches, relatively cheap operation. In this study, results of our experiments with suspension spraying of yttria-stabilized zirconia (YSZ) with WSP torch are presented and demonstrate that coating deposition with a high feed rate is possible with WSP technology. Formation of both columnar “cauliflower” microstructure and segmentation cracks was achieved. Variation of the deposition conditions was observed to modify coating microstructure in terms of splat morphology, porosity and thickness per pass, which is promising for further coating development.