Numerical assessment of thermal insulation and stress responses in film-cooled turbine vane thermal barrier coatings under CMAS deposition conditions

Abstract

Deposition of CaO-MgO-Al₂O₃-SiO₂ (CMAS) significantly contributes to the spalling of thermal barrier coatings (TBCs) on turbine vanes. A thorough understanding of the thermodynamic properties during CMAS deposition is critical for advancing the lifetime design of TBCs. This study employs the CMAS gas thermal shock test to determine the deposition characteristics, which were then analyzed using the critical velocity model. The results of this analysis align closely with experimental outcomes. Based on the numerical simulation of the fluid-solid coupling method, we further explored the insulation efficiency and stress distribution in TBCs under CMAS deposition conditions. It was observed that CMAS predominantly accumulates on the pressure side and within the film pores of the vane TBCs, with minimal deposition on the suction side. Such deposition patterns result in an increased overall temperature of the vane, concurrently diminishing the TBCs' insulation efficiency. Specifically, CMAS deposition raised the maximum surface temperature of the vane by 100 K and decreased the peak insulation performance of the TBCs by 16 %. Additionally, the deposition induced higher stresses within both the TBCs and the underlying vane substrate, with a 7 % increase in the maximum principal stresses at the TBC surface and a 6 % increase in the substrate. Consequently, under CMAS deposition conditions, TBCs in regions of low insulation efficiency and high stress on turbine vanes are prone to cracking and subsequent spallation.