Air plasma-sprayed high-entropy (Y_0.2Yb_0.2Lu_0.2Eu_0.2Er_0.2)₃Al₅O₁₂ coating with high thermal protection performance

High-entropy rare-earth aluminate (Y_0.2Yb_0.2Lu_0.2Eu_0.2Er_0.2)₃Al₅O₁₂ (HE-RE₃Al₅O₁₂) has been considered as a promising thermal protection coating (TPC) material based on its low thermal conductivity and close thermal expansion coefficient to that of Al₂O₃. However, such a coating has not been experimentally prepared, and its thermal protection performance has not been evaluated. To prove the feasibility of utilizing HE-RE₃Al₅O₁₂ as a TPC, HE-RE₃Al₅O₁₂ coating was deposited on a nickel-based superalloy for the first time using the atmospheric plasma spraying technique. The stability, surface, and cross-sectional morphologies, as well as the fracture surface of the HE-RE₃Al₅O₁₂ coating were investigated, and the thermal shock resistance was evaluated using the oxyacetylene flame test. The results show that the HE-RE₃Al₅O₁₂ coating can remain intact after 50 cycles at 1200 ℃ for 200 s, while the edge peeling phenomenon occurs after 10 cycles at 1400 ℃ for 200 s. This study clearly demonstrates that HE-RE₃Al₅O₁₂ coating is effective for protecting the nickel-based superalloy, and the atmospheric plasma spraying is a suitable method for preparing this kind of coatings.