Supersonic Screw Dislocations Gliding at the Shear Wave Speed

The motion of dislocations bridges the atomistic-scale deformation events with the macroscopic strength and ductility of crystalline metals. In particular, screw dislocations, whose Burgers vector is parallel to the line, play crucial roles on plastic flow. Nevertheless, their speed limit and its stress dependence remain controversial. Using large-scale molecular dynamics simulations, we reveal that full screw dislocations and twinning partial screw-type dislocations can glide steadily at the speed of shear wave velocity. Such a scenario is excluded in existing theories due to energy dissipation singularity. We conclude that both types of screw dislocations can move supersonically. We further observe that the motion of a screw dislocation also depends on the shear stress components, which do not contribute to the resolved shear stress (RSS), in contrast to the conventional Schmid's law, which states that the motion of a dislocation is determined by the RSS.