Thermo-mechanical modelling of functionally graded thermal barrier coatings

The introduction of oxygen diffusion barrier such as alumina is one of the promising solutions to use Ni-based superalloys with TBC for longer periods. Three types of TBC systems containing alumina are proposed in this study. Residual thermal stresses at room temperature were calculated for the proposed systems using a linear plate model. In the case of a layered composite system (stabilized zirconia / alumina / bond coat), tensile stresses in the bond coat are shown to be much higher than its yield limit. If a pure bond coat layer was replaced by an alumina / bond coat graded layer was under zirconia layer, the stress distribution significantly depends on the profile of concentration. TBC systems containing metal-rich graded layer were found to have substantially reduced thermal stresses. The system of stepwise FGM is more promising from the standpoint of thermal stress relaxation.