Effect of CMAS penetration behavior on stress evolution in TBCs under three-dimensional temperature gradients

Abstract

CaO–MgO–Al2O3–SiO2 (CMAS) penetration is the primary failure mode of thermal barrier coating (TBC) film cooling systems, and therefore, understanding the CMAS penetration behavior and its effect on the internal stress evolution of TBCs is necessary. In this study, the effect of nonuniform CMAS penetration on the stress profile of a top ceramic (TC) coating layer was investigated under a nonuniform temperature field with three different mainstream temperatures (1561, 1623, and 1673 K). Further, a conjugate heat transfer numerical model was established to determine the temperature distribution in the TBCs with a gas-film cooling system. A phase-field model was adopted to study the CMAS penetration behavior. Moreover, the effects of CMAS penetration on the temperature distribution, growth rate of the thermal growth oxide (TGO), and residual stress are discussed. The CMAS penetration continuously eroded the TC layer, following the temperature distribution trend. CMAS penetration achieved temperature increments of 26.1, 35.1, and 40.3 K at the TC/TGO interface and TGO thickness differences up to 0.12, 0.26, and 0.37 μm after 500 h oxidation at the three mainstream temperatures. A significant increase in the residual stresses of the TBCs caused by CMAS penetration was observed. The von Mises stress increased from 243.7, 295.7, and 339.9 MPa to 367.0, 391.5, and 414.9 MPa, respectively. Driving forces for Mode I and Mode II interfacial cracks at the trailing edge of the cooling hole increased with CMAS penetration, and the increase in the mainstream temperature enhanced the driving forces.