CMAS Corrosion Behavior of Mid-Entropy Rare-Earth Hafnate (Y_0.3Gd_0.3Yb_0.4)₄Hf₃O₁₂ as Thermal Barrier Coating Candidate

High-temperature CMAS corrosion has become a crucial factor inhibiting the further development of thermal barrier coatings (TBCs) because of the increasing service temperature of aero-engines. Herein, a novel mid-entropy rare-earth hafnate (Y_0.3Gd_0.3Yb_0.4)₄Hf₃O₁₂ (YGYbH) was prepared by ultrafast high-temperature sintering (UHS) technology, and its CMAS corrosion behavior and mechanism were investigated. During corrosion, the Ca₂RE₈(SiO₄)₆O₂ apatite phase with a lower formation enthalpy and entropy-stabilized effect had a more intense tendency to be generated, which improves the density and stability of the reaction layer, hindering the further penetration of molten CMAS. Moreover, the significant lattice distortion caused by the rare-earth ions with different radii impeded the ionic diffusion, which delayed the CMAS corrosion reaction. In general, YGYbH, with excellent CMAS corrosion resistance, has the potential to serve as a next-generation TBC material.