Corrosion behaviour of La2Hf2O7 thermal barrier coatings against molten CMAS melts at 1300 and 1500 °C

Thermal barrier coatings (TBCs) are susceptible to accelerated degradation caused by molten calcium-magnesium-alumino-silicate (CMAS), which exhibits a significant challenge to design and develop durable TBCs. Rare-earth hafnates are regarded as promising TBCs candidates. In this study, the corrosion behaviour of plasma-sprayed La2Hf2O7 coating at 1300 and 1500 degrees C was investigated and compared with the traditional YSZ coating. The study indicated that the La2Hf2O7 exhibited better corrosion resistance than the YSZ. During the corrosion process, La2Hf2O7 coating dissolved into CMAS melts and reprecipitated m-HfO2 and apatite which effectively mitigate the corrosion, while the YSZ coating only produced ZrO2 with a transition from tetragonal to monoclinic phase. The recession depth of the coatings increases noticeably when the reaction temperature raised from 1300 to 1500 degrees C. The YSZ coating failed at 1500 degrees C, while the La2Hf2O7 coating still remained intact. This study may provide a theoretical basis for selecting and design of rare-earth hafnates TBCs with excellent corrosion resistance.