Comparison of glide mechanisms in hcp Ti and Ti₃Al

Several dislocation glide mechanisms are studied in Ti and Ti₃Al by means of in situ straining experiments in a transmission electron microscope at various temperatures. The prismatic glide of α titanium occurs by the jerky motion of straight screw a-dislocations subjected to a frictional force. An explanation for the discontinuity in the temperature dependence of the corresponding activation area is proposed, on the basis of the experimentally measured variation of the corresponding dislocation jump length. In Ti₃Al, superlattice 2a-dislocations exhibit two different dissociation modes in prismatic planes corresponding to highly different antiphase boundary energies. The properties of these two types of dislocation are compared and discussed. It is shown that the motion of 2c+a superlattice dislocations in pyramidal planes is controlled by a new mechanism: the self-nucleation of small-size obstacles as the result of irreversible atomic displacements. The tension/compression asymmetry observed between type 1 and type 2 pyramidal planes is finally discussed.