The influence of second phase Ti₃Al on the deformation mechanisms in TiAl

Abstract

Dislocations in samples of a heat-treated and quenched two phase Ti-46at.% Al alloy have been characterized, and those with Burgers vectors, b, given by b=½<1l0] and b=½<112] have been observed. The microstructure of deformed samples is characterized mainly by dislocations with b=½<1l0]. These dislocations have high Peierls stresses in TiAl of nominal purity, because of the directionality of bonds between the Ti atoms. Therefore, the present observations have been interpreted on the basis that the phase Ti₃Al getters the interstitial elements from the TiAl, since the solubility of these elements in the former phase is significantly larger than in the latter. It is proposed that the removal of interstitials from TiAl in this way decreases the degree of directionality of bonding between the Ti atoms, and so reduces the anisotropy in Peierls stresses caused by these directional bonds. A relatively large number of twins have also been observed in the lamellae of TiAl, and this may be interpreted on the same basis, namely that the mobility of dislocations with b=⅙<112], the twinning dislocations, is also increased when the concentration of interstitial elements is reduced.