A large-deformation mechanical-thermal-chemical coupling model for thermal barrier coatings incorporating strain gradient effects

The growth of the thermally grown oxide (TGO), formed during the oxidation of thermal barrier coatings (TBCs) in advanced gas turbine engines, exhibits a pronounced size effect as the thickness approaches its grain size. Addressing the gap in current coupling theories for capturing scale-dependent oxidation behavior, this study further develops an enhanced theoretical framework that integrates large deformation mechanical-thermal-chemical coupling, incorporating strain gradient effects. By utilizing the Green strain as an independent field variable, numerical solutions were obtained using a mixed finite element method. The growth kinetics of the TGO are investigated under isothermal conditions. Numerical results indicate that the strain gradient effect increases the compressive stress within the TGO growth region by 77.8 % and promotes a more uniform stress distribution with increasing scale parameters. Consequently, the growth rate and non-uniform expansion of the TGO are substantially mitigated, as the stress-induced inhibition effect is more effectively utilized. With suppressed non-uniform expansion of the TGO, the susceptibility of the coating to surface wrinkling diminishes with larger scale parameters. This research is instrumental in elucidating the oxidation dynamics of TBCs.