Recent progress in the coating protection of gamma titanium aluminides

Engine designers show continued interest in titanium aluminides based on the intermetallic gamma-TiAl phase as lightweight structural materials to be used at moderately elevated temperatures. Although alloy development has made significant progress in terms of mechanical properties and environmental resistance, protective coatings have been developed that help to extend the lifetime of these alloys significantly. The major challenge of coating development is long-term stability of a protective oxide scale that forms during service for which purpose alumina formation is essential. Furthermore, changes of coating chemistries at high temperatures must be controlled to avoid rapid degradation of the coatings due to diffusional losses into the substrate material and vice versa.