Simulation of bond coat properties in thermal barrier coatings during bending

Analytical models are presented for predicting bond coat properties of thermal barrier coatings (TBCs) during crack propagation studies induced by bending. Studies on crack propagation behaviour in TBCs were performed with plasma spray coated zirconia, bonded by a MCrAlY layer to Ni-base superalloys (Inconel 617 and CMSX-4). Such thermal barrier composites are currently considered as candidate materials for advanced gas turbine stationary components. Coating as a protective layer improves the surface properties of the substrate. At a temperature of 1073 K, the crack propagation was found to be confined to the TBC (ceramic layer), as the ductile bond coat offers an attractive sink for stress relaxation. The stress-strain behaviour is a function of the elastic modulus of coating, bond coat as well as that of substrate. Thus, from a knowledge of the elastic modulus of TBC and that of substrate, the elastic modulus of the bond coat needs to be evaluated which is a basic parameter for characterizing coating performance. In this paper, the elastic modulus of the bond coat has been determined by modifying the existing model for a two-layered composite beam to a three-layered composite beam.