Processing parameter effects on solution precursor plasma spray process spray patterns

Solution precursor plasma spray (SPPS) is a promising process for making thermal barrier coatings (TBCs) with improved durability. The improved durability of SPPS TBCs results from the novel microstructural features, (i) absence of splat boundaries, (ii) generation of through-thickness vertical cracks (iii) existence of uniformly distributed porosity. In this process, the coating is built up by the overlapping and stacking of layers deposited in each pass of the plasma torch across the substrate. Information concerning the lamella is generally referred to as the spray pattern. The spray patterns from SPPS of 7wt.%Y2O3–ZrO2 precursor were studied via a fixed scan spray method, where the plasma torch repeatedly scans on a single line across the substrate. The surface of the resulting spray patterns can be divided into adherent deposits and powdery deposits that correspond to the hot and cold regions of the plasma jet, respectively. The penetration depth of the liquid into the plasma jet has a significant effect on the position of the adherent deposits and the deposition efficiency. The structure of the adherent deposits across the section normal to the motion of plasma torch is symmetric about its center. It becomes more porous and the thickness of the deposits is reduced towards the edges. Implications of these results for understanding and improving the SPPS process are discussed.