Residual stress mapping in high yttria thermally sprayed zirconium oxide coatings

Need for high thermal efficiency in aero and land-based turbine engines push the envelope for low conductivity and high strength thermal barrier coatings (TBC’s). Prominent approach towards achieving this is through high yttria content in zirconia to stabilize zirconia . High yttria content degrades the thermal shock resistance of the TBC system. The project therefore aims to explore the residual stress profile of 8YSZ (as sprayed) and 20YSZ (in as sprayed and thermal shock conditions). Mapping residual stresses will provide qualitative information on the thermal shock life of the TBC system thereby eliminating the need of expensive and time-consuming thermal shock studies on all the possible chemistries. Due to the heavy lattice distortion unleashed by the high atomic number rare earth elements, it is expected that neutron diffraction would be able to predict the residual stress and quantify the thermal shock. Neutron diffraction residual strain analysis is expected to expedite the selection of the best composition that would suit both the requirements of thermal shock resistance as well as low thermal conductivity. Reduced tensile residual stress are known to be beneficial to the fatigue life of coatings leading to enhanced thermal cycling behavior – which demonstrates wider impact of this investigation.