Evaluation of major factors influencing the TBC topcoat formation in axial suspension plasma spraying (SPS)

Abstract

AbstractSuspension plasma spraying (SPS) is ideally suited to produce porous or dense columnar, strain‐tolerant thermal barrier coatings (TBCs) and also offers the possibility of producing other microstructures such as feathery and dense vertically cracked coatings. The specific properties of the TBC are significantly influenced by the formed microstructure, that is, affected by feedstock material and process parameters. In this work, the effects of various process parameters in the SPS process are investigated. It was found that the suspension feed rate has a significant effect on the microstructure, especially on the column density of the coating, whereas the suspension solids content mainly affects the coating porosity. Additionally, the surface roughness and topography of the bond coat are crucial for the formation of columnar coatings and were therefore investigated. Despite comparable roughness values for as‐sprayed bond coats for high velocity oxy fuel and vacuum plasma spray produced coatings, the surface structures differ significantly from each other and affect the microstructure of the deposited topcoat. Characterization of mechanical properties by means of micro‐indenter can be suitable for columnar coatings to determine Young's modulus within a column. However, due to the heterogeneity of the coating, the method is not suitable to describe the mechanical properties of the topcoat.