Engineered nanoscale coherent twin boundaries (CTBs) offer an effective approach for achieving a good combination of high strength and reasonable ductility in materials. In order to optimize the properties of materials by tailoring the geometry and structure of CTBs, numerous studies have been carried out to elucidate the mechanisms of deformation involving CTBs. Twin boundary migration is so far the only experimentally observed mode of boundary motion involving twinned FCCmetals. Therefore, it has been widely held that CTBs cannot slide.According tothe isolated molecular dynamics studies, computational simulations point to the possibility of CTB sliding at low temperatures and under limited conditions, but no significant twin boundary sliding has been experimentally documented so far.

Through theoretical analysis, it is quantitatively shown that CTB sliding should be possible at least for specific loading orientations, thus a general orientation map for CTB migration and CTB sliding can be developed. By using in situquantitative mechanical testingon nanotwinned copper pillars inside a transmission electron microscope (TEM), for the first time it has been demonstrated that CTBs can slide, which validates the results of the theoretical analysis and proves the quantitative predictions previously made.

The findings established both experimentally and theoretically the occurrence of significant CTB migration, and this is contrary to the generally held notion. New mechanistic insights were added to the deformation mechanisms of CTBs, a major topic of relevant literature in the past decade that has received growing interest during this time. To complement the general scientific interest, the present results are expected to offer valuable insights into ways in which the design of micro- and nano-structures involving CTBs could be accomplished, thus further optimizing material properties and performance.

This work has been published on Nature Communications. The following people authored the article: Dr. Wang Zhangjie, PhD candidate Li Yao, Huang Longchao, and Prof. Shan Zhiwei from the CAMP-nano of XJTU, PhD candidate Li Qingjie and Prof. Evan Ma from Johns Hopkins University, Prof. Lu Lei from the Institute of Metal Research of Chinese Academy of Sciences, Dr. Dao Ming and Prof. Li Ju from the Massachusetts Institute of Technology, Prof. Subra Suresh from Nanyang Technological University are the authors.

This study was supported by the Natural Science Foundation of China (51231005, 51401159, and 51621063), the "973 Program (the national development project on key basic research)" of China (2012CB619402), and the "111 project"(the discipline innovation and talent introduction project in the institutions of higher learning) (B06025).