Melting index characterization and thermal conductivity model of plasma sprayed YSZ coatings

The melting index of particle was measured to quantitatively characterize the spraying parameters of as-sprayed YSZ coatings. Moreover, new and reliable representation of melting index was achieved, using in-flight particle temperature and velocity. The prediction of microstructure features, such as total porosity and spheroidal porosity of as-sprayed coatings, could be available by the quantitative relationship between melting index and porosity. Based on the real microstructure characteristics, finite element models were generated to simulate heat transfer and calculate thermal conductivity of coatings. The large deviation between the experimental thermal conductivity and simulation results was attributed to the influence of microcracks, which was not shown in as-analyzed images due to resolution limit. Taking all the effects of microcracks and porosity into account comprehensively, the calculation model of thermal conductivity was established with the calculated error lower than 10%.