Influence of preheating temperature on splat morphology of spray deposited yttria-stabilized zirconia and lanthanum magnesium hexaaluminate in thermal barrier coatings

Abstract

The performance of thermal barrier coatings (TBCs) depends upon the morphology of individual splats and how a single particle flattens. A splat is a single unit cell of thermal barrier coatings. Its properties significantly influence the overall performance of the coating. The transition temperature of the substrate affects the splat morphology and also influences the adhesion strength of the applied coating.  This study investigates the effect of substrate preheating temperature on splat morphology and the critical transition temperature for yttria-stabilized zirconia (8YSZ) and lanthanum magnesium hexaaluminate (LaMgAl₁₁O₁₉, LaMA) powders deposited via atmospheric plasma spray (APS).  Using scanning electron microscopy (SEM), a critical transition temperature of 400°C was identified for both materials. At this temperature, disc-shaped splats with improved adhesion formed, while irregular shapes were observed below 400°C, and disordered morphologies appeared above it. Notably, at 400°C, 8YSZ splats exhibited surface cracks, whereas LaMA splats remained crack-free, highlighting differences in their thermo-mechanical properties. These findings emphasize the importance of optimizing preheating temperature to achieve desirable splat morphology and enhance TBC performance.