On the evolution of stresses due to lattice misfit at a Ni-superalloy and YSZ interface

The principle of elastic strain energy minimization is used to predict the possible ranges of allowable lattice misfit for the formation of coherent and semi-coherent interfaces between a Ni superalloy substrate and a cubic yttria stabilized zirconia (c-YSZ) ceramic coating. Depending upon the elastic modulus, failure strength in compression and tension, and the Burgers vector of the film material, the magnitude of allowable lattice misfit can vary over a wide range. It is shown that compressive stresses as high as several gigapascals may exist at the coherent YSZ films, and a higher positive lattice misfit can sometimes be more favorable for the formation of a semi-coherent interface than is a lower negative lattice misfit. Both coherency and the effect of lattice misfit on the interfacial stress decrease with an increase in the thickness of the film. The effect of lattice misfit on the evolution of interfacial stresses during film deposition must be considered during the design of dissimilar materials interfaces and for the prediction of interfacial delamination and the fracture of films.