Investigation of the CMAS thermal corrosion resistance of novel Al2O3/YTaO4 thermal barrier coatings

Abstract

In this paper, atmospheric plasma spraying was used to produce YTaO₄ thermal barrier coatings and 10 wt% Al₂O₃-YTaO₄ thermal barrier coatings. The coatings were heated to temperatures of 1300 °C and 1600 °C, respectively. The corrosion resistance and mechanism of the coatings against CMAS corrosion at 1250 °C for 10 h and 50 h were then investigated. This study revealed that during CMAS thermal corrosion, the primary corrosion products were anorthite, apatite, and Ca₂Ta₂O₇. Apatite and Ca₂Ta₂O₇ formed a compact layer at the boundary between the reaction layer and the coating layer, effectively blocking CMAS melt infiltration in a downward direction. As the heated temperature increased, the volume expansion resulting from the phase transformation and the closure of pores and microcracks within the coating caused the coated surface to become denser. The corrosion rate of the coatings was reduced due to a reduction in grain boundaries and a lower concentration of defects in the grain boundary regions. This improved the resistance of coatings to CMAS thermal corrosion. The presence of Al₂O₃ facilitated the formation of anorthite in the CMAS melt. Excessive anorthite can form a thick network that hinders the penetration of the CMAS melt. Meanwhile, it increased the viscosity of the melt and reduced its ability to spread, resulting in a slower rate of penetration by the CMAS melt. This, in turn, improved the coatings' ability to withstand thermal corrosion caused by CMAS.