Influence of microstructure on the erosion behaviour of suspension plasma sprayed thermal barrier coatings

Suspension Plasma Spraying (SPS) is a promising technique for thermal barrier coating (TBC) applications by virtue of its ability to produce a porous-columnar microstructure. Such a microstructure bears promise to combine the benefits of both conventional electron beam physical vapour deposited (EB-PVD) as well as atmospheric plasma sprayed (APS) columnar and porous microstructures, respectively. Significant research has been devoted to understand the effect of microstructure on thermal conductivity and lifetime of SPS TBCs. However, limited studies have so far targeted the erosion behavior of SPS TBCs, which is an important performance criterion for TBCs operating in erosive environments. Therefore, this work aims to study the influence of various microstructures produced by SPS on the erosion behavior of TBCs. Six different coating microstructures were produced using SPS employing identical spray conditions with distinct suspension characteristics achieved by utilizing varying solvent type, particle size distribution and solid load content. The as-sprayed TBCs were subjected to an air jet erosion test, and their erosion resistance was compared. Results showed significant influence of porosity on the erosion behavior, with lower porosity resulting in superior erosion resistance. Furthermore, a vertically cracked microstructures with negligible unmolten regions exhibited superior erosion performance compared to a columnar microstructure.