Sintering and mud cracking in EB-PVD thermal barrier coatings

A multi-scale model is presented for the evolution of microstructure, sintering and deformation of columnar EB-PVD thermal barrier coatings. Computational studies are presented of the sintering of a coating constrained by a rigid substrate. It is demonstrated that the sintering process can become unstable when the in-plane stiffness exceeds a critical value. Imperfections in the coating can develop into cracks, which propagate through the thickness of the coating, creating a pattern of “mud cracks”. The simulations have motivated the development of simplified models of this process which describe the sintering response and the development of mud cracks in terms of the evolution of a small number of degrees of freedom. These simple models capture the major features of the more detailed computational simulations. They also allow the conditions under which imperfections grow into cracks to be readily identified and predict a density of mud cracks that is consistent with experimental observations.