Effects of oxygen on the deformation behaviour in single-phase γ-TiAl alloys

The effect of the interstitial solute element oxygen on the mobility of dislocations in single-phase γ-TiAl alloys has been assessed experimentally. Thus polycrystalline samples of alloys of Ti-52 at.% with oxygen impurity levels of either 750 or 1250wt p.p.m. have been deformed at room temperature. It has been found that, while extensive glide of dislocations with Burgers vectors b given by b = 1/2(110) is observed for higher purity specimens, their activity is very much reduced at increasing levels of oxygen impurity contents. Thus, plastic deformation of samples with an oxygen level of 1250 wt p.p.m. is provided essentially by glide of superdislocations with b = (101), accompanied by superlattice extrinsic stacking fault formation. Possible mechanisms for this effect are discussed.