A dislocation model was proposed for twin formation, in the L10 structure, under a compressive applied stress along the c-axis. It was based upon the classic pole mechanism for twinning in the face-centered cubic structure. The dissociation of a jog, on an ordinary [110]/2 dislocation, into a Shockley and Frank partial was energetically favorable according to anisotropic elasticity theory. Whereas a pile-up of [10¯1] super-dislocations assisted a Shockley loop to spiral around 2 sessile nodes, the Frank partial expanded under mechanical and chemical stresses and mitigated the high repulsive interaction between 2 Shockley partials. Published data on the apparent critical resolved shear stress for twinning in Ti-56at%Al single crystals were explained by assuming reasonable values for a local stress concentration factor, and a vacancy supersaturation at high temperatures.

On the Dislocation Pole Mechanism for Twinning in TiAl Crystals M.H.Yoo: Philosophical Magazine Letters, 1997, 76[4], 259-68