Thermomechanical degradation mechanisms of high-entropy (Yb0.25Er0.25Ho0.25Y0.25)2SiO5 environmental barrier coatings under CMAS melt infiltration

This study examines the thermomechanical degradation mechanisms of a high-entropy (Yb_0.25Er_0.25Ho_0.25Y_0.25)₂SiO₅ (4REMS) environmental barrier coating under CMAS melt infiltration. The investigation considers both isothermal and thermal cycling conditions. Under isothermal exposure, the 4REMS coating exhibited excellent corrosion resistance due to the formation of a continuous apatite reaction layer that effectively inhibited melt infiltration. The synergistic dissolution of Yb^3 + , Er³⁺, Ho³⁺ and Y³⁺ cations in the CMAS melt promoted the formation of this dense layer. However, during cyclic corrosion testing, the emergence of microcracks compromised the structural integrity of the reaction layer, leading to an accelerated penetration rate of corrosive species. Furthermore, periodic temperature fluctuations induced dynamic instabilities in the dissolution-precipitation equilibrium, resulting in pronounced morphological alterations of apatite grains, including enhanced nucleation and coarsening.