High-temperature performance and failure behavior of A6B2O17 (A = Hf, Zr; B = Ta, Nb) high-entropy thermal barrier coatings prepared by atmospheric plasma spraying

High-entropy A 6 B 2 O 17 (A = Hf, Zr; B = Ta, Nb)/8YSZ double-layer ceramic coatings with three compositions are fabricated by atmospheric plasma spraying (APS). Thermal cycling tests are performed at 1150 °C with a 5 min heating hold followed by 5 min air cooling, while isothermal oxidation tests are performed at 1150 °C. Among the three coatings, H 3 Z 1 T 2 N 1 coating exhibits the longest thermal cycling lifetime (1823 ± 153 cycles), followed by the H 1 Z 1 T 2 N 1 coating (1123 ± 136 cycles) and H 1 Z 3 T 2 N 1 coating (826 ± 114 cycles). After 180 h oxidation, the thermally grown oxide (TGO) thicknesses are 5 μm, 5.6 μm, and 6.6 μm, respectively. The H 3 Z 1 T 2 N 1 coating possesses the lowest oxidation rate constant ( k p = 0.1263 μm 2 ·h −1 ). This superior performance is attributed to dense vertical cracks induced by higher thermal expansion, which relieve thermal stress, suppress oxygen ingress, and delay interfacial failure.