OXIDATION OF INTERMETALLIC ALLOYS IN TI-AL-NB TERNARY-SYSTEM

The isothermal oxidation behavior of intermetallic alloys over a wide range of compositions in the Ti-Al-Nb system was investigated in a temperature range from 900 to 1,200-degrees-C. The results showed that the Al content and the ratio of Ti-to-Nb of the alloys affected the oxidation behavior in this ternary system. Al improved the oxidation resistance of alloys. ff the ratio of Ti-to-Nb was either too high or too low, the oxidation resistance was reduced dramatically. The oxide constituents were determined. The formation of an integral protective Al2O3 scale-layer was the basic condition for good oxidation resistance. A composition range of the alloys, having excellent oxidation resistance, was suggested. A map summarizing the results of the oxidation resistance and the oxide scale type was established. The oxidation mechanism was also discussed.