Depending on working parameters, plasma spraying process allows to achieve original metallic and/or ceramic coating microstructures varying from quite dense to high porosity materials. Combined to the versatility of the process in terms of coating shaping, this leads to an extended field of applications. For instance, porous coatings are required for stress accommodation or filtering applications due to their high specific area, whereas dense coatings are needed for the electrolyte in S.O.F.C technology. Past works have shown that porosity is not a convenient parameter to describe completely coating microstructure and that the main difficulty is to find a unique parameter capable to describe the microcrack network and pores distribution. In this paper we propose a fractal approach of coating microstructure based on confocal microscopy of fluorescent impregnated coatings. Fractal dimensions as well as porosity data are given and analyzed for various plasma-spayed coating microstructures. This work is a contribution to characterize plasma-sprayed coatings. Coatings properties are related to the microstructure which depends on the spraying process.

The influence of plasma spraying parameters on the mechanical properties of coatings has been studied. ZrO2-Y2O3 coatings were sprayed onto stainless steel and aluminium substrates at temperatures of about 75°C and 225°C. An original set of samples, facilitating the measurement of substrate deflection, was used to evaluate the effect of thermal cycling under different spraying conditions. In order to correlate thermal cycling values and mechanical properties to coating microstructure, the coatings were impregnated with low-viscosity resin and examined under a confocal microscope. The results reveal the influence of spraying temperature, substrate properties, and torch-substrate velocity on coating damage.