Compositional dependence of the deformation behaviour of ultrahigh-purity Ti-Al alloys

Abstract

The present study is concerned with the effect of the O and Al concentrations on the deformation behaviour of ultrahigh-purity (UHP) Ti-(48, 50, 52) at.% Al alloys using UHP Ti with 30 wt ppm O. It has been shown that yield strength increases with increasing O content. Stoichiometric Ti- 50 at.% Al alloys had the lowest yield strength and the highest ductility when the O content was sufficiently low. It is suggested that the deformation mechanism of UHP binary Ti- Al is strongly related to the Al concentration. The deformation substructure of UHP Ti-48 at.% Al is shown to be dominated by ordinary dislocation as well as deformation twinning and a small portion of superdislocations. The deformation substructure of UHP Ti-50 at.% Al alloy was similar to that of Ti-48 at.% Al, but deformation twinning was not observed. Most of dislocation structures of UHP Ti-52 at.% Al alloy consisted of faulted dipoles. The major deformation mode of UHP Ti-48 at.% Al and UHP Ti- 50 at.% Al alloys was ordinary dislocation in deformation orientation, which takes advantage of ordinary dislocation slip. However, the major deformation mode in this orientation for UHP Ti-52 at.% Al alloys was superdislocation slip.