Explanation of the discrepancy between the measured and atomistically calculated yield stresses in body-centred cubic metals

Abstract

We propose a mesoscopic model that explains the discrepancy (at a factor of 2–3) between experimentally measured yield stresses of bcc metals at low temperatures and typical Peierls stresses determined by atomistic simulations of isolated screw dislocations. The model involves a Frank–Read-type source emitting dislocations that become pure screws at a certain distance from the source and, owing to their high Peierls stress, control its operation. However, due to the mutual interaction between emitted dislocations, the group consisting of both non-screw and screw dislocations can move at an applied stress that is a factor of 2–3 lower than the stress needed for the glide of individual screw dislocations.