Quantitative characterization of microstructures of plasma-sprayed coatings and their conductive and elastic properties

Quantitative characterization of microstructures of plasma-sprayed coatings that accounts for their anisotropic and "irregular" character is developed. Dominant microstructural features are identified. It is found, in particular, that small "islands" of partial contacts along microcracks produce a strong effect on the conductive and elastic properties and constitute a major microstructural feature. The role of porosity is two-fold: (1) it has only a minor effect on the conductive and elastic properties, as compared with the effect of cracks (for porosities less than 15%) and (2) higher levels of porosity appear to be an indicator of higher crack density. Effective conductive and elastic properties are given in terms of the proper microstructural parameters. Cross-property connections that interrelate the conductive and the elastic properties are given in an explicit form. They can be used for optimization of the microstructure for the combined conductive and elastic performance. The developed framework is applied to yttria-stabilized-zirconia (YSZ) coatings. It is demonstrated that the framework can be directly linked to microstructural data obtained from photomicrographs. Predictions made on the basis of the microstructural analysis were tested against experimental data on elasticity/conductivity. The agreement is generally good. (C) 2004 Elsevier B.V. All rights reserved.