Insights into service-derived Zr-Ta-O film: Morphology evolution, temperature resistance, and atomic bonding

Entropy-stabilized ceramics for ultra-high temperature oxidation protection are springing up, accompanied by complex morphology characteristics and elusive protective mechanisms. Herein, how the Ta/Zr molar ratio change affected the morphology evolution, temperature resistance, and atomic bonding of Zr-Ta-O film was revealed, which was expected to deepen the understanding on A-B-O protective film (A = Hf, Zr; B = Ta, Nb). The Zr-Ta-O film was constructed on the thermally sprayed ZrC-TaC coating utilizing oxyacetylene ablation. Morphological characteristics of the Zr-Ta-O film were found highly related to Ta/Zr molar ratios. The long-term temperature endurance limit of the service-derived Zr-Ta-O film was considered below 2000 ℃, affected by the consumption of micro-scale Ta-rich regions under high-temperature gas scouring (∼2800 ℃, 5–8 m/s). The phenomena were well explained by the binding energy difference (Ta-doped t-ZrO₂ and Zr-doped α-Ta₂O₅) and fluctuation law of Zr-O bond length with Ta/Zr molar ratio increasing (from local instability to whole instability).