High temperature thermal shock resistance of plasma‐sprayed high‐entropy (Y _0.2 Yb _0.2 Ho _0.2 Er _0.2 Tm _0.2 ) ₂ Hf ₂ O ₇ coating

Abstract Rare earth hafnates are considered to have great application potential in the field of thermal protection due to their relatively higher melting point and lower thermal conductivity. Based on the multi‐principal element high‐entropy design concept, a novel high‐entropy (Y 0.2 Yb 0.2 Ho 0.2 Er 0.2 Tm 0.2 ) 2 Hf 2 O 7 (HE‐YYb) as top coating was deposited by air plasma spraying. In this study, exploring the thermal shock resistance behaviors of the HE‐YYb coating was carried out by the plasma flame shock test. Results indicate the HE‐YYb coating has only impact pits in the central ablation area and no peeling phenomenon at 1300°C. However, at 1400°C, the surface edge position of the coating occurs fragmented peeling but remains a defect fluorite structure, the unique high‐entropy effect of the material significantly improves thermal shock performance and high temperature phase stability of HE‐YYb coating. Additionally, the HE‐YYb coating only exhibited edge delamination and cracking after 13 cycles of the furnace cycle test at 1200°C for 300 s, which effectively alleviates thermal stress concentration, indicating that the coating possesses thermal shock resistance. This study clearly shows that the novel HE‐YYb coating expands the application prospects of high‐entropy rare earth oxide coatings in thermal protection coatings.