Examination of the effect of YSZ/α-Al2O3 interphase upon the thermo-mechanical behaviour of thermal barrier coating using hybrid MD-FE simulations

Abstract

The adhesion strength of thermal barrier coatings (TBC) is governed by the interphase between the top coat (TC) and the thermally grown oxide (TGO). In most existing continuum work, the thermomechanical property of this interphase is either ignored or described using rudimentary methods. To address this deficiency and determine reliable thermomechanical properties for that interphase, we conducted comprehensive molecular dynamics (MD) simulations of the three affected interphases: TC, TGO and the cohesive interphase between them. Three aspects of the work were examined. First, we conducted extensive research to carefully select the Coulomb-Buckingham interatomic potential parameters needed for the accurate description of TC and TGO atomistic systems. Second, Young's modulus (E), coefficient of linear thermal expansion (α) and thermal conductivity (κ) were determined using MD simulations. Third, the results from MD simulations were used in finite element (FE) model to determine the continuum behaviour of the 3-phases of the TBC. The results show that at TC/TGO interphase, a cohesive bond is formed, and that Young's modulus of the interphase decreases with increased temperature. Our results further reveal that the thermal expansion of YSZ is restricted by α-Al2O3 at the interphase. Additionally, we show that the thermal resistance at the interphase is negligible. Lastly, the results obtained from the newly proposed MD-FE framework show that the assumption of line interphase will grossly overestimate the effective stiffness of YSZ/α-Al2O3 system.