Oxidation protection of γ-TiAl-based alloys – A review

• Comprehensive comparison of coating concepts for the environmental protection of intermetallic γ-TiAl alloys.
• Evaluation of the long-term performance of the different coatings during exposure between 800 and 1050 °C.
• The main evaluation criterion is based on the mass gain after at least 1000 h of high temperature exposure.
• Detailed overview of the chemical stability of the different coating types (overlay, diffusion and halogen based) is included.
• Assessment of the coatings processing routes along with their advantages and drawbacks.

Alloys based on γ-TiAl are lightweight materials with attractive mechanical properties at high temperatures. Although these alloys reveal a superior resistance against environmental attack compared to titanium and 2-based alloys, efficient protection is required for industrial applications at temperatures between 800 and 1050 °C. Extensive research in order to solve this problem started more than 30 years ago. This review provides a summary of the different concepts based on surface modification techniques developed for the environmental protection of γ-TiAl alloys at high temperatures, including overlay and diffusion coatings, as well as the halogen effect. The discussion includes a comparison between the most promising coating types under long-term high temperature exposure and an assessment of their processing routes from a technological point of view. Therefore, a mass gain of 1 mg/cm2 after at least 1000 h of exposure was set as a benchmark to evaluate these protection systems.

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