HIGH-TEMPERATURE OXIDATION OF TI3AL-NB ALLOYS

Titanium aluminide (Ti3Al-Nb) has potential for high-temperature appli cations because of its low density and high-temperature strength. This research is aimed at improving the high-temperature oxidation resista nce of a Ti3Al-Nb alloy by modification of its composition. The oxidat ion rates of Ti3Al-Nb alloys were measured from 600 to 900 degrees C i n air. The oxide layer was examined by X-ray diffraction, scanning ele ctron microscopy, and electron probe microanalysis. The experimental r esults reveal that alloys with added Nb tend to form denser oxide laye rs 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 inve stigators. The only exception is a Ti65Al25Nb10 alloy, which shows bet ter oxidation resistance than the commercial Ti65Al24Nb11 alloy. The o xidation resistance of Ti65Al25Nb10 alloy can also be improved slightl y by the addition of small amounts of Si or Cr. An increase in the oxi dation resistance of Ti65Al25Nb10 alloy containing Y was observed at 9 00 degrees C but not at 800 degrees C or below. The parabolic oxidatio n rate equation is adequate to describe the high-temperature oxidation reaction of the Ti3Al-Nb alloys in the atmosphere.