Structural characterization of 101̅1 twin boundaries in deformed cobalt

• The interfacial structure of 101̅1 twinning boundaries investigated by HRTEM.
• The actual 101̅1 TB is not straight, but presents a step-terrace interfacial feature.
• High density basal stacking faults are observed experimentally within the 101̅1 twin.

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, 101̅1 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 101̅1 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 101̅1 deformation twin in deformed cobalt has been investigated. The results show that the twinning boundaries are not straight, but actually consist of 101̅1 TBs and {0002}||1̅011 basal-pyramidal interfaces. In addition, a high density of basal stacking faults is also observed experimentally within the 101̅1 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.