Extended strips of superlattice intrinsic stacking fault, which resulted from the planar dissociation of 2 types of glissile super-dislocation and a sessile ordinary dislocation, were analyzed on the basis of elastic anisotropy, effect of applied stress, and relative dislocation mobility. The dislocation mechanism for twin nucleation was considered with special reference to the apparent critical resolved shear stress. It was noted that the spontaneous dissociation of a ½[110] edge dislocation into Frank-Shockley partials was favorable in L10 alloys, including TiAl, because of a repulsive interaction in the direction normal to the (111) plane. A pile-up of super-dislocations, of (111)[10¯1]-type, against a Lomer-Cottrell barrier or a forest dislocation of ½[110]-type, was suggested to produce the necessary internal stress concentration. The early stages of twin formation via a pole mechanism were geometrically and energetically easier to overcome in L10 alloys than in face-centered cubic metals and alloys. It was concluded that no conclusive experimental evidence for a specific twin nucleation mechanism in the L10 structure existed, although recent transmission electron microscopic results on TiAl had furnished support for pole mechanisms, a pile-up mechanism, and an overlapping mechanism.

Dislocation Mechanisms for Deformation Twinning in the L10 Structure M.H.Yoo: Scripta Materialia, 1998, 39[4-5], 569-75