Structural evolutions and failure mechanisms of APS tantalate high-entropy ceramics coatings response to thermal cycle up to 1500 ºC

Thermal barrier coatings (TBCs) with high working temperatures and long service life are indispensable for the hot-end components of gas turbines and aircraft engines. This work designs and verifies that tantalate high-entropy ceramics (HECs) coatings are excellent TBCs with working temperatures reaching 1500 °C. We reveal the structural evolutions and failure mechanisms of tantalate HECs coatings synthesized via the air plasma spraying (APS), after they are subjected to thermal shock at 1500 ºC for 614 times, thermal fatigues at 1150 ºC for 12830 times, and annealing at 1100 ºC for 384 h. The thermal stress caused by temperature gradient, differences in thermal expansion coefficients (TECs) and mechanical properties between ceramic coatings and bond coat (BC) lead to the spalling of coatings during thermal shock, while the effects of BC oxidization are limited. In thermal fatigues, the accumulative thermal stress between BC and thermal growth oxides (TGO) is higher than the fracture resistance when the <em>h/R</em> ratio is higher than 0.32 (<em>h</em> and <em>R</em> are the TGO thickness and undulation radius, respectively), which mainly leads to spalling of coatings. Additionally, the effects of coatings sintering and stiffness are also considered, which lead to their surficial spalling during the high-temperature service. Two different failure mechanisms are proposed based on their microstructural evolutions, and the synthesized tantalate HECs coatings can be used at temperatures up to 1500 ºC, which further promote the designs and applications of high-performance TBCs.&nbsp;