Microstructure and phase evolution of Yb₂SiO₅/MoSi₂-Mullite environmental barrier coatings on niobium alloy at 1500 °C

Water-vapor corrosion behavior of Yb₂SiO₅/MoSi₂-Mullite double-layer environmental barrier coating on Nb based alloy at 1500 °C was investigated systematically. Initially, the thermal grown oxide (TGO, mainly SiO₂) appearing undulating morphology was generated at the interface of Yb₂SiO₅/MoSi₂-Mullite. Then, undulation characteristics of TGO layer were gradually weakened, and the maximum tensile stress near TGO layer reduced by ∼36%. With the internal diffusion of Yb₂O₃ and the generation of gaseous water-vapor corrosion substance, pores in the Yb₂SiO₅ layer, acting as diffusion paths for oxygen, induced continual thickening of TGO with an approximately line law, resulting in horizontal cracking near the TGO layer.