Process-Geometry Interplay in the Deposition and Microstructural Evolution of 7YSZ Thermal Barrier Coatings by Air Plasma Spray

Abstract

Air plasma spray (APS) yttria-stabilized zirconia (7YSZ) TBCs are often deposited onto model planar surfaces for microstructural evaluation and testing. Recently, an interest on the implications of both TBC deposition and performance on more complex geometries has developed in the scientific and industrial community, as the microstructures can be substantially different depending on the substrate geometry with concomitant implications on performance (e.g. leading-edge failure). In this study, the implications of processing TBCs on cylindrical substrates as opposed to planar surfaces are explored. Particle diagnostics were conducted to understand differences in coating formation dynamics between planar and cylindrical targets. Scanning Electron Microscopy and Image Analysis were concurrently used to quantitatively define the porosity differences among multiple conditions of spraying and to benchmark the transition of porosity from disk to cylinder. Additionally, rods of different radii of curvature were explored in this study to evaluate the effect of the radius of curvature on the TBC deposit microstructure. Finally, a modified approach to established thermoelastic beam curvature techniques is introduced which can see subtle changes in the mechanical properties of coatings produced at torch traverse conditions similar to how they are produced on a curved surface.