Mullite based compositions have interest for thermal barrier coatings because they have thermal expansion coefficients close to those of silicon ceramic substrates. In this work, mullite-zirconia coatings are obtained by flame spraying and characterized based on microstructure, crystal phases, hardness, elastic modulus, and thermal conductivity. Crystallinity is improved by in-situ heating with a flame torch, which is also shown to increase hardness and elastic modulus. Thermal diffusivity measurements show that the thermal properties of mullite-zirconia coatings are relatively stable over a wide temperature range and adequate for many thermal barrier applications.

CaZrO 3 coatings were alternatively prepared by air plasma spray and flame spray processes. The microstructural characteristics and crystalline phases of the coatings were comparatively studied as a function of the spraying temperature achieved with each technique and the stand off distance. Image analyses were used to estimate their porosity. Thermal diffusivity was measured on free-standing thick coatings using the laser flash technique. Thermal conductivity was obtained from the experimental thermal diffusivity and density data. The hardness of the coatings was evaluated by Vickers indentation tests. Finally, different thermal treatments were carried out to evaluate the evolution of the crystalline phases and the properties of the coatings.