A study was made of the twinning mechanism and operating twin system of a face-centred tetragonal L10 θ-MnNi phase in an equi-atomic Mn-Ni alloy by using detailed transmission electron microscopic analysis (electron diffraction, high-resolution imaging and Z-contrast imaging techniques) of the structure of twins formed during the β (B2, bcc) to θ (L10, fct) phase transformation. In addition to the well-documented (111)1/6<112] deformation twinning system in L10 crystals, (111)1/6<211]*-type pseudo-twin systems were also observed (in <ijk], i and j were interchangeable in the tetragonal system but k was not). The Z-contrast image of the twins showed that no atomic shuffling occurred during twinning in the θ-MnNi phase, and that atomic order was maintained in the (111)1/6<112] type true twins.

The Twin and Twin System in FCT L10 θ-MnNi Phase in an Equiatomic Mn-Ni Alloy. Y.U.Heo, H.C.Lee: Materials Transactions, 2007, 48[10], 2546-50