Finite difference thermal model for a thermal barrier coating with alumina growth

This thesis presents a one-dimensional finite difference thermal model that characterizes heat transfer in a thermal barrier coating (TBC) and substrate system. Results of both standard and vertically cracked TBCs have been presented. The effect of the growth of the thermally grown oxide (TGO) layer on the temperature distribution has been considered as well. The TGO layer, principally composed of aluminum oxide, initially plays a salutary role as it serves to keep the other two layers of the TBC system, namely, the metallic bond coat and ceramic top coat firmly bonded. During operation, however, the TGO layer continues to grow as a result of the continuous ingress of oxygen through the porous ceramic top coat and migration of aluminum from the bond coat, in the prevailing high temperature environment. Governing heat transport equations have been formulated using constitutive thermo-physical properties of the different components of the system. Cognizant of the fact that TGO formation is essentially a chemical process during which alumina is formed in the presence of heat, a growth kinetics model which characterizes the change in dimensions of the TGO layer as a function of time and temperature, forms an integral part of the proposed mathematical model. With the implementation of the requisite boundary conditions, while using a finite difference solution methodology executed in MATLAB, it is possible to track the location of the interface between the TGO layer and the bond coat, while determining the temperature distribution in the entire TBC - Substrate system.