Low-temperature stiffening of air plasma-sprayed 7 wt% Y₂O₃-stabilized ZrO₂

Evolution in bending modulus and accompanying microstructure of free-standing air plasma-sprayed Y₂O₃-stabilized ZrO₂ subjected to thermal exposure, from 800°C to 1300°C, has been studied. The bending modulus was measured using custom-made miniaturized cantilevers, which was loaded using a nanoindenter. Variation in the bending modulus was compared with the density change. The coating shows two domains of behavior of modulus variation with density: the low temperature/time domain wherein the bending modulus doubles without measurable change in the density and the high-temperature domain where modulus increases monotonically with density. Finite element (FE) analysis was carried out using cross-sectional micrographs of coatings to measure the elastic modulus of the actual coating and compared with experimentally observed values. The modulus values predicted by FE analysis are 70%-80% higher than the experimentally observed values. An analytical model has been proposed to corelate the microcracks density and elastic modulus, which is in reasonable agreement with the experimentally measured values.