Texture formation in alpha-alumina coating by aerosol deposition method

Reference Presenter Authors
09-106 Makoto Tanaka Tanaka, M.(Japan Fine Ceramics Center); Kawashima, N.(Japan Fine Ceramics Center); Kitaoka, S.(Japan Fine Ceramics Center); Yokoe, D.(Japan Fine Ceramics Center); Kato, T.(Japan Fine Ceramics Center); Hasegawa, M.(Yokohama National University); Thermal and environmental barrier coatings (T/EBCs) for SiC fiber-reinforced SiC ceramic matrix composites (CMCs) are critical for application of these composites to hot-section components such as next-generation gas-turbine engines. We have previously proposed T/EBCs that reflect thermal energy, for use with CMCs. These T/EBCs had a periodic structure consisting of alternate Al2O3 and Al-doped Y2Ti2O7 layers, which have very different refractive indices. The T/EBCs were prepared by aerosol deposition (AD), which is capable of producing dense layers at room temperature. It is generally accepted that Al2O3 layers formed by AD will have random crystal orientations. However, we found that the layers produced by this process had a fiber texture consisting of (0001) basal planes. Because these basal planes have a low surface energy than other planes, such Al2O3 layers would be expected to exhibit excellent corrosion resistance when used in T/EBCs. However, the relation between the texture and the AD coating conditions is still unclear. This texture is considered to be formed due to slipping of Al2O3 particles from the jet upon impact with the substrate. Therefore, in the present study, we examined the relation between the jet particle impact velocity and the texture of the layers. The results indicated that for low impact velocities, the particles underwent plastic deformation, and dense layers with a basal fiber texture were formed. On the other hand, for high impact velocities, the particles fractured, and the fiber texture corresponded to the (10-14) cleavage planes. At even higher particle impact velocities, a porous microstructure was produced and no texture was present.
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