Curvature behaviour of multilayer specimens of thermal barrier systems

The impact of residual stresses on the elastic and plastic deformation behavior of plasma sprayed and physical vapor deposited thermal barrier systems was studied. In particular, multilayer specimen strips composed of plasma sprayed partially stabilized zirconia, oxidation resistant NiCoCrAlY bond-coat and Ni-based superalloy substrate were tested. The experiments focused on the in-situ observation of specimen curvature during thermal cycling between room temperature and 1000 degreesC. The mechanical response of specimens with different layer thickness was analyzed with a thermoelastic model to derive elastic modulus and thermal expansion of the ceramic top coat, both parameters as a function of temperature. With the thermoelastic data of all three layers, the residual stress distribution could be calculated analytically. The results of the two coating variants are compared. The deviation from thermoelastic behavior at higher temperature is discussed in terms of stress relaxation in the bond coat due to plastic deformation.