Hot Corrosion Behavior of Lapo4-Ysz Thermal Barrier Coating Exposed to Molten Calcium-Magnesium-Alumino-Silicate (Cmas) at 1250°C-1350°C

Abstract

The calcium-magnesium-alumina-silicate (CMAS) corrosion behavior of LaPO4-YSZ thermal barrier coatings (TBCs) was investigated at 1250°C-1350°C for 4 hours. Corrosion was observed to occur primarily at the grain boundaries, and the corrosion depth increased with increasing temperature. The melt infiltration reaction layer formed after CMAS corrosion was primarily composed of ZrO2, residual CMAS, and La-apatite (Ca2+xLa8-x(SiO4)6-x(PO4)xO2), regardless of the temperature. It was worth noting that a continuous dense reaction layer was formed after the corrosion test at 1250 °C, which further delayed the infiltration of CMAS. However, the molten CMAS could infiltrate into the coating more easily when the temperature exceeds 1300 °C, leading to more severe corrosion. The results show that the CMAS corrosion behaviors of coating at different temperatures were primarily controlled by the infiltration and reaction processes; When temperatures exceed 1300°C, CMAS infiltration becomes the dominant process due to the reduced viscosity of the CMAS melt.

Keywords: Thermal barrier coatings, CMAS resistance, Infiltration, grain boundary, La-apatite