The deformation twinning which took place within lamellar samples during creep deformation at strain rates as low as 10-7/s was found to be closely related to the motion, piling-up and dissociation of interfacial (Shockley partial) dislocations. Since the interfacial (Shockley partial) dislocations were energetically unsuitable for undergoing cross-slip or climb under normal conditions, they could only move conservatively along interfaces. Thus a pile-up configuration, once generated, could not easily be dissipated and therefore remained in place even at high temperatures. Dislocation pile-ups eventually led to the emission of deformation twins from the interfaces and into γ lamellae when the local stress concentration due to the dislocation pile-up became sufficiently large. Deformation twinning of {111}<11¯2> and {11¯2}<111> types (both generating Σ = 3 twin boundaries) was observed. Both types of twinning could be rationalized by supposing dislocation mechanisms which involved the core dissociation

of interfacial dislocations: 1/6[¯12¯1](111) → 1/6[011](100) + 1/6[¯11¯2]](¯1)11 and 1/6[1¯21](111) → 1/2[0¯10](001) + 1/6[111](11¯2), and the emission of 1/6<¯11¯2> and 1/6<111> twinning dislocations into γ lamellae to form (¯111)[¯11¯2]- and (11¯2)[111]-type twins, respectively. The critical shear stress for {111}<11¯2>-type twinning was evaluated by using the Peach–Koehler formula, based upon the pile-up configuration of interfacial dislocations.

Interfacial Dislocations and Deformation Twinning in Fully Lamellar TiAl. L.M.Hsiung, T.G.Nieh, B.W.Choi, J.Wadsworth: Materials Science and Engineering A, 2002, 329-331, 637-43