Damage quantification and failure mechanism of EB-PVD thermal barrier coatings under CMAS corrosion

In this work, the corrosion resistance mechanism and the destructive behavior of thermal barrier coatings (TBCs) under CaO-MgO-Al₂O₃-SiO₂ (CMAS) corrosion condition were elucidated through the utilization of authentic volcanic ash powders. Based on the buckling theory, an interface damage accumulation model of TBCs under CMAS corrosion was established from surface critical compressive strain. Furthermore, the evolution law of the surface critical compressive strain of TBCs under different corrosion time was determined through room temperature compression tests combined with digital image correlation (DIC) technology. The research findings indicate that the columnar crystal gaps and pores in the top coat (TC) layer serve as channels for CMAS penetration, allowing CMAS to penetrate the entire TC layer in a short period of time. The infiltration of CMAS will alter the mechanical properties of TC layer, resulting in increase of the Young's modulus and hardness of the TC layer. Consequently, microcracks appear at the TC/TGO interface during CMAS corrosion, ultimately leading to delamination and spalling at the TC/TGO interface. Finally, a comprehensive understanding of damage accumulation processes in TBCs under CMAS corrosion is achieved by establishing a relationship between damage and corrosion time, realizing cross-scale correlation between the macroscopic spalling in TBCs and microscopic interfacial damage mechanisms. This study provided a quantitative test method for assessing corrosion-induced damages in TBCs.