Molecular dynamics investigation of deformation twinning in γ-TiAl sheared along the pseudo-twinning direction

In spite of being sheared along the so-called pseudo-twinning [2¯11] direction, γ-TiAl undergoes true twinning under zero pressure or hydrostatic tension by means of a specific combination of 16[2¯11], 16[1¯21¯] and 16[1¯1¯2] shears in two consecutive (1 1 1) matrix planes allowing the adjacent twin to thicken over one (1 1 1) atomic layer. The corresponding total shear strain of 22 is four times as large as that generated by conventional deformation twinning or during the L10 to L11 transformation by 16[112¯] or 16[2¯11] shears, respectively. This shear is substantially more effective in accommodating stress concentration and high strain rate than conventional deformation twinning. The conditions under which twinning by 23[2¯11] dislocations operates are interpreted based on a modified gamma-surface and discussed in terms of zonal partial dislocations.