Oxidation behavior of titanium aluminides of high niobium content

The oxidation behaviour of two titanium aluminides of composition Ti–24Al–20Nb and Ti–24Al–27Nb were studied in oxygen in the range 1125–1325 K. The parabolic rate constants of the alloys in the present investigation were higher than that of titanium aluminides of lower Nb content [Ti–24Al–11Nb and Ti–24Al–15Nb (Roy TK, Balasubramaniam R, Ghosh A. Metall Mater Trans A 1996;27A:3993)]. The major constituent of the oxides was TiO2 while Nb2O5 and Al2O3 were the minor constituents. The formation of Nb2O5 as a separate phase is possibly related to the lower oxidation resistance of these alloys compared to titanium aluminides of lower Nb content.