Energy landscapes of (2¯1¯1)<111> deformation twinning in body-centered cubic Mo and (111)<11¯2> deformation twinning in face-centered cubic Al and Cu were determined using density functional theory for sliding of layers numbering up to 7. In body-centered cubic Mo, the minimum thickness of a metastable twin was two layers, while twin embryos of 3 and 4 layers were unstable. Starting from 5 layers, the Mo twin could grow in a layer-by-layer fashion. The twin boundary formation and migration energies were found to be 607 and 40mJ/m, respectively, implying that partial dislocations on twin boundaries will have wide cores and high mobilities. The stress to homogeneously nucleate a partial loop on the boundary of a thick twin was determined to be only 1.4GPa, indicating that once a deformation twin in Mo reaches a critical thickness, which was estimated to be 6 layers, it could grow rather easily. Based upon simple defect mechanics considerations, it was estimated that the condition for runaway defect growth required the twin embryo thickness to be of the order of tens of layers. Upon comparing the twinning energy landscape for Mo, with those of Al and Cu, it was found that the former had a longer-ranged interlayer mechanical coupling, which was due to angular bonding and to weaker electron screening in the intervening layers. With regard to Al and Cu, the interactions in the former were relatively longer-ranged.

Energy Landscape of Deformation Twinning in BCC and FCC Metals. S.Ogata, J.Li, S.Yip: Physical Review B, 2005, 71[22], 224102 (11pp)