Structural characterization of {10(1)over-bar1} twin boundaries in deformed cobalt

Deformation twinning is one of the most important strain accommodation mechanisms for deformed hexagonal close-packed materials. During plastic deformation, interfaces such as twinning boundaries usually play a critical role to affect the mechanical properties of many materials with hexagonal structure. As one kind of significant twinning modes, {10 (1) over bar1} contraction twin usually occurs at the final stage of plastic deformation and serves to relax the stress concentration. Therefore, it is very crucial to understand the interfacial structure of twinning boundaries of {10 (1) over bar1} twin at the atomic scale if we are to properly tailor twins for microstructural design and applications. In the present work, by means of high-resolution transmission electron microscopy, the flail deformation twin in deformed cobalt has been investigated. The results show that the twinning boundaries are not straight, but actually consist of {10 (1) over bar1} TBs and (0002)parallel to{(1) over bar 011} basal-pyramidal interfaces. In addition, a high density of basal stacking faults is also observed experimentally within the {10 (1) over bar1} twin. According to these experimental features, the possible mechanism for twinning boundary migration and for the emergence of such abundant basal SFs will be discussed. (C) 2016 Elsevier Inc. All rights reserved.