Alumina-zirconia composite coatings were fabricated by plasma spraying using both of mixture of commercial feedstocks and agglomerated feedstock from fine powders of about 100 nm. The coating from mixture had an ordinary lamella structure which consisted of alumina splats and zirconia splats, whereas that from fine powders showed the striped contrast in the splat. X-ray deflection profiles revealed that the latter contained gamma-alumina, monoclinic-zirconia and tetragonal-zirconia crystals, which sizes were under 10 nm. These facts mean the fine crystals dispersed inhomogeneously. The nano-composite coating had a higher Vickers hardness and lower thermal diffusivity than the coating from mixture. Moreover, it showed good thermal stability and its crystallite size kept under 50 nm even after the heat treatment at 1500°C for 100h.

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