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.

Acknowledgments

The authors would like to thank Dr F. Louchet, Dr L. Kubin and Dr D. Vesely for stimulating discussions on experimental observations of screw dislocations in bcc metals. This research was supported by the US Department of Energy, BES Grant no. DE-PG02-98ER45702.