Numerical study on effects of interfacial roughness and microcracks on stress distribution in thermal barrier coatings with temperature drop.

Abstract

This paper establishes a finite element model that includes the interface roughness characteristics to evaluate the stress concentration in the atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) with an uneven temperature field. We further scrutinize the effects of crack initiation at the interface between the thermally grown oxide (TGO) and the bond coat (BC) and in the ceramic top-coat (TC) on stress redistribution by introducing the debonding model for crack analysis. Results indicate that the interfacial residual stress σ₂₂ achieves the critical value at the end of the cooling stage. As the temperature drop intensifies, the σ₂₂ declines at the interface while it escalates within the TC. However, the interfacial crack propagation results in the redistribution of stress in the TBCs, and the σ₂₂ changes from tensile stress to compressive stress in the peak of the TC. The propagation rate of the interfacial crack accelerates with a smaller temperature difference and a thicker initial TGO. When the TGO/BC interfacial morphology is uniform, the crack growth rate is the most rapid. The stress redistribution leads to an off-peak tensile stress concentration area in the TC and increased maximum tensile stress near the horizontal micro-crack tip. The concentration area of σ₁₁ occurs in the TC above the peak of the interface, indicating that the vertical crack in the TC is likely to initiate above the peak.