Resistance of (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 top-coat material in thermal/environmental barrier coatings to calcium-magnesia-alumina-silicon attack at 1300 °C and 1500 °C

Rare earth elements (Dy, Ho, Er, Tm, and Lu), characterized by low-diffusivity in silicate melts, were designed as defect-fluorite structure high-entropy material (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 to determine its resistance to calcium-magnesia-alumina-silicon (CMAS) attack. The results indicate that corrosion reactions preferentially crystallize anorthite and garnet phases in the front of molten CMAS at 1300 °C, which alleviates rapid infiltration of CMAS. The reaction between the melt and (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 forms mixture layers comprising apatite and fluorite phases at 1500 °C, which are accompanied by the prompt exhaustion of CMAS. The capability of intaking RE determines the formation mechanisms of apatite with two different structures. The study reveals that the high-entropy material effectively resists molten CMAS attack at 1300 °C; however, its effectiveness in preventing rapid corrosion decay diminishes at 1500 °C. Factors affecting reaction control were discussed at each condition to elucidate the interactions between the multi-cation hafnate material and silicate deposits. This study represents a significant stride towards advancing high-entropy hafnate thermal barrier coating material applications in aerospace engineering.