THE OXIDATION AND PROTECTION OF GAMMA-TITANIUM ALUMINIDES

The excellent density-specific properties of the gamma class of titani um aluminides make them attractive for intermediate-temperature (600-8 50 degrees C) aerospace applications. The oxidation and embrittlement resistance of these alloys is superior to that of the alpha(2) and ort horhombic classes of titanium aluminides. However, since gamma alloys form an intermixed Al2O3/TiO2 scale in air rather than the desired con tinuous Al2O3 scale, oxidation resistance is inadequate at the high en d of this temperature range (i.e., greater than 750-800 degrees C). Fo r applications at such temperatures, an oxidation-resistant coating wi ll be needed; however, a major drawback of the oxidation-resistant coa tings 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.