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 deg C) aerospace applications. The oxidation and embrittlement resistance of these alloys is superior to that of the alpha sub 2 and orthorhombic classes of titanium aluminides. However, since gamma alloys form an intermixed Al sub 2 O sub 3 /TiO sub 2 scale in air rather than the desired continuous Al sub 2 O sub 3 scale, oxidation resistance is inadequate at the high end of this temperature range (i.e., > 750-800 deg 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 on the Ti-Al-Cr system offers the potential for improved fatigue life.