Abstract
A technique to synthesize in-situ α-Al2O3 composite coating on TC11 is explored for protecting titanium alloys against oxidation at high temperature. Results reveal that an oxygen barrier composite coating is formed on the substrate at 1073 K, which is composed of the compact α-Al2O3 layer and transition layer. It is effective to protect TC11 from the internal and external oxidation, the oxidation rate and average oxide thickness of in-situ composite coating are much less and thinner than those of substrate. At 973 K, The rate and thickness with the composite coating are 0.01 mg2/cm4·h and 3 μm, in comparison with 0.1 mg2/cm4·h and 28 μm of the substrate after high temperature oxidation after 100 h. At higher temperature 1073 K, the composite coating also apparently improves the oxidation resistance (0.03 mg2/cm4·h) compared with the non-coated substrate (7.95 mg2/cm4·h). It was observed outward oxidation at 1073 K for the composite coating by XRD and SEM-EDS analysis, which is due to the fact that Ti diffused towards the coating surface and formed Al2TiO5. Finally, the oxidation resistance mechanism was discussed. The overall diffusion coefficient is reduced by the formation of the α-Al2O3 layer. And the oxidation is inhibited by reducing substrate surface oxygen partial pressure by composite coating.
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