HIGH-TEMPERATURE OXIDATION OF TI3AL-NB ALLOYS

Titanium aluminide (Ti3Al-Nb) has potential for high-temperature applications because of its low density and high-temperature strength. This research is aimed at improving the high-temperature oxidation resistance of a Ti3Al-Nb alloy by modification of its composition. The oxidation rates of Ti3Al-Nb alloys were measured from 600 to 900 degrees C in air. The oxide layer was examined by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The experimental results reveal that alloys with added Nb tend to form denser oxide layers and that oxidation rate can be reduced by increasing Nb content (up to 11 at.% in this study), which is in good agreement with other investigators. The only exception is a Ti65Al25Nb10 alloy, which shows better oxidation resistance than the commercial Ti65Al24Nb11 alloy. The oxidation resistance of Ti65Al25Nb10 alloy can also be improved slightly by the addition of small amounts of Si or Cr. An increase in the oxidation resistance of Ti65Al25Nb10 alloy containing Y was observed at 900 degrees C but not at 800 degrees C or below. The parabolic oxidation rate equation is adequate to describe the high-temperature oxidation reaction of the Ti3Al-Nb alloys in the atmosphere.