The oxidation and protection of gamma titanium aluminides

The excellent density-specific properties of the gamma class of titanium aluminides make them attractive for intermediate-temperature (600-850 degrees C) aerospace applications. The oxidation and embrittlement resistance of these alloys is superior to that of the alpha(2) and orthorhombic classes of titanium aluminides. However, since gamma alloys form an intermixed Al2O3/TiO2 scale in air rather than the desired continuous Al2O3 scale, oxidation resistance is inadequate at the high end of this temperature range (i.e., greater than 750-800 degrees C). For applications at such temperatures, an oxidation-resistant coating will be needed; however, a major drawback of the oxidation-resistant coatings currently available is severe degradation in fatigue life by the coating. A new class of oxidation-resistant coatings based in the Ti-Al-Cr system offers the potential for improved fatigue life.