Strong crystal size effect on deformation twinning

There are two main mechanisms at play when a crystal undergoes deformation: ordinary dislocation plasticity and deformation twinning. While the former is known to be dependent on the size of the crystal, hence influencing sample strength at the nanoscale, the latter's size dependence has not been explored to date. Ju Li and colleagues show, using microcompression and nanoindentation experiments, that deformation twinning is completely suppressed in crystals smaller than a micrometre in size, giving way to ordinary dislocation plasticity as the only deformation mode. This may be because deformation twinning is a collective phenomenon that cannot operate for small crystal sizes. The discovery paves the way for new approaches to manipulating the mechanical properties of materials at the microscale.