Improvement in the Self-healing Property of Plasma-Sprayed Environmental Barrier Coatings by SiC Addition

Abstract

Environmental barrier coatings (EBCs) protect SiC/SiC ceramic matrix composites from steam oxidation. Yb2Si2O7 is a promising ceramic material for the top coating of the EBCs. However, thermal shock and foreign object debris can cause cracks on the surface of an EBC, thereby reducing its ability to overcome environmental barriers. It has been found that an EBC can be strengthened by adding SiC to its top coating; this addition heals the cracks present on the EBC when subjected to high-temperature oxidation. In this study, the SiC contents of Yb2Si2O7 coatings prepared using atmospheric plasma spraying (APS) were evaluated to identify the structure and composition of the coatings. The results of crack-healing tests show that the Yb2Si2O7/SiC granulated powder could retain SiC particles in the coatings after the spraying, whereas in Yb2Si2O7/SiC mixed powder, the SiC particles evaporated during APS, indicating that Yb2Si2O7/SiC granulated powder can be used as the feedstock powder in self-healing EBCs. The time-dependent changes in surface crack closure and Yb2Si2O7/SiC granular powder coating remediation caused due to high-temperature oxidation were also evaluated. It was found that the reliability of self-healing EBCs could be improved by appropriately controlling the particle size and SiC content in the coatings.