Plastic anisotropy and associated deformation mechanisms in nanotwinned metals

Anisotropic plastic deformation in columnar-grained copper in which preferentially oriented nanoscale twins are embedded is studied by experimental testing, crystal plasticity modeling and molecular dynamics simulations. The dominant deformation mechanism can be effectively switched among three dislocation modes, namely dislocation glide in between the twins, dislocation transfer across twin boundaries, and dislocation-mediated boundary migration, by changing the loading orientation with respect to the twin planes. The controllable switching of deformation mechanisms not only leads to a marked dependence of yield strength on loading orientation, but also induces a strong orientation dependence of strain hardening that can be critical for retaining tensile ductility. These results demonstrate a new route for tailoring both nanostructure and loading to control the deformation mechanisms in order to achieve the desired mechanical properties in engineering materials.