Unveiling the Corrosion Mechanisms of High-Entropy RETaO₄ Through In Situ Observation

The ambiguous understanding of calcium-magnesium aluminosilicate (CMAS) corrosion mechanisms in RETaO₄ has hindered performance optimization through rare-earth compositional engineering. This study systematically investigates the corrosion behavior of 3-10 component RETaO₄ systems. In situ X-ray diffraction/Transmission electron microscope coupled with Electron backscatter diffraction analysis unveils dynamic reaction pathways during the pre-corrosion heating stage, identifying the crystallization and growth patterns of dominant corrosion product pyrochlore-structured (Ca_2-a-bRE_aAl_b)(Ta_2-c-dMg_cSi_d)O₇. A reaction-diffusion mechanism of CMAS corrosion for RETaO₄ is proposed, highlighting the different behaviors of various rare earth elements in the corrosion process. Among eight types of RETaO₄, La_1/6Nd_1/6Sm_1/6Eu_1/6Gd_1/6Dy_1/6TaO₄ exhibits the best corrosion resistance, with a relatively thin corrosion layer and the ability to avoid element segregation and localized infiltration. These findings establish composition-property relationships for designing next-generation corrosion-resistant thermal barrier coatings.