R. Pflumm, S. Friedle, M. Schütze
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.