Recent Progress in the Coating Protection of Gamma Titanium Aluminides

Abstract

Engine designers show continuing interest in titanium aluminides based on intermetallic γ-TiAl phase as light–weight structural materials to be used at moderately elevated temperatures. Although alloy development has made significant progresss in terms of environmental resistance, protective coatings have been developed that help to extend the lifetime of these alloys significantly. The major challenge of coatings developments is long-term stability of a protective oxide scale that forms during service for which purpose alumina (Al₂O₃) formation is essential. Furthermore, changes of coating chemistries at high temperatures must be controlled in order to avoid rapid degradation of the coatings due to diffusional losses into the substrate material. The paper describes recent work of the authors on metallic Ti-Al-Cr and Ti-Al-Cr-N coatings. Moreover, an attempt will be described to apply thermal barrier coatings on γ-TiAl in order to further push their useful service temperatures to higher limits.