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A novel TiAl 3 /Al 2 O 3 composite coating was prepared on γ-TiAl alloy. The process included two steps: (1) TiAl 3 /Al 2 O 3 composite powders were prepared by high energy ball milling of pure Al and nano-TiO 2 powders, followed by a heat-treatment; (2) the as-prepared composite powders were deposited on γ-TiAl substrate by cold spray. The cyclic oxidation was conducted at 900 °C to test the performance of the composite coating. The results showed that the composite coating had good crack resistance and effectively decreased the oxidation rate of the substrate. [ABSTRACT FROM AUTHOR]

A novel silicon-aluminizing diffusion coating was prepared on γ-TiAl alloy by cold sprayed Al-12Si alloy coating and subsequent heat treatment. The oxidation resistance of silicon-aluminizing diffusion coating was studied at 900 °C for 1000 h and 120 cycles. The results showed that the coating decreased the inward oxygen diffusion and thus improved the oxidation resistance of bare alloy effectively. The microstructure evolution of the diffusion coating was investigated. Possible mechanisms related to the oxidation and elements diffusion behavior were also discussed. [ABSTRACT FROM AUTHOR]

Abstract: The TiAl3–Al composite coating on orthorhombic Ti2AlNb based alloy was prepared by cold spray. Oxidation in air at 950°C indicated that the bare alloy exhibited poor oxidation resistance due to the formation of TiO2/AlNbO4 mixture and intended to scale off at the TiO2 rich zone. A nitride layer about 2µm was formed under the oxide layer. The oxygen invaded deeply into the alloy and caused severe microhardness enhancement in the near surface region. The TiAl3–Al composite coating exhibited parabolic oxidation kinetics and showed no sign of degradation after oxidized up to 1098h at 950°C in air under quasi-isothermal condition. No scaling of the coating was observed after oxidized at 950°C up to the tested 150 cycles. The major oxide in the oxidized coating was Al2O3. The AlTi2N, TiAl and small amount of TiO2 were also observed in the oxidized coating. The EPMA and microhardness tests showed that inward oxygen diffusion was prevented by the interlayer, which was formed between the composite coating and the substrate during heat-treatment. Microstructure analyses demonstrated that the interlayer play a major role in protecting the substrate alloy from high temperature oxidation and interstitial embrittlement. [Copyright &y& Elsevier]