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 (Dy 0.2 Ho 0.2 Er 0.2 Tm 0.2 Lu 0.2 ) 2 Hf 2 O 7 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 degrees C, which alleviates rapid infiltration of CMAS. The reaction between the melt and (Dy 0.2 Ho 0.2 Er 0.2 Tm 0.2 Lu 0.2 ) 2 Hf 2 O 7 forms mixture layers comprising apatite and fluorite phases at 1500 degrees 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 degrees C; however, its effectiveness in preventing rapid corrosion decay diminishes at 1500 degrees 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.