Interfacial reaction-induced bilayer multicomponent barrier in plasma-sprayed Y₂O₃/YSZ coatings for superior CMAS corrosion resistance

Calcium-magnesium-alumino-silicate (CMAS) corrosion threatens the durability of thermal barrier coatings (TBCs) in aero-engines. To address this, we developed an atmospheric plasma-sprayed (APS) Y₂O₃/YSZ bilayer coating that forms an in-situ bilayer multicomponent barrier against molten CMAS. Through interfacial reaction studies at 1300 °C, we identified a dense apatite-garnet barrier layer. Experiments reveal two Y-apatite phases: Ca₂Y₈(SiO₄)₆O₂ dominates at Y³⁺-rich interfaces, forming a dense apatite layer; while Ca₄Y₆(SiO₄)₆O crystallizes in Ca²⁺-rich regions, consuming basic oxides to increase CMAS viscosity. Prolonged exposure further yields Y-garnet phase, establishing a secondary protective barrier. First-principles DFT calculations confirm that Ca₂Y₈(SiO₄)₆O₂ exhibits the highest thermodynamic stability, with a formation enthalpy of −355.087 kJ/mol and a cohesive energy of −8.127 eV/atom, rationalizing its dominance in the barrier layer. This bilayer multicomponent barrier composed of apatite and garnet layers, effectively and completely blocks CMAS infiltration after 24 h, demonstrating exceptional protection for next-generation TBCs against CMAS corrosion.