Hot corrosion of Gd2M2O7 (M = Zr, Hf) thermal/environmental barrier coatings subjected to calcium-magnesium-alumina-silicate melts at 1300 and 1500 °C

The new generation of T/EBCs requires their top layer materials with good resistance to severe corrosion by CMAS. Rare-earth zirconates/hafnates with pyrochlore structure are regarded as promising candidates for T/EBC. In this work, the corrosion behaviours and mechanisms of plasma-sprayed Gd2M2O7 (M=Zr, Hf) coatings at 1300 and 1500 °C for 4 - 25h were investigated. The Gd2M2O7 coating showed good corrosion resistance under long-term corrosion at 1300°C. The Gd2M2O7 coatings reacted with CMAS and precipitated apatite and fluorite, forming a dense layer that can prevent further penetration of CMAS. However, the CMAS penetrated into the Gd2M2O7 coatings because of the sharply decreased viscosity of the CMAS as the temperature raised to 1500°C, forming another infiltration layer. The results also suggested that the Gd2Hf2O7 possessed better resistance to CMAS corrosion than Gd2Zr2O7.