Quantitative understanding of anomalous slip in Mo

Abstract

Hexagonal dislocation networks (HDNs) formed by the reaction of <1 1 1>/2 screw dislocations are frequently observed in association with anomalous slip in body-centred cubic (bcc) metals. However, its role assigned in anomalous slip remains obscure due to the absence of quantitative description of its response to uniaxial loading. Here, systematic atomistic simulations are performed in molybdenum (Mo) to study the responses of a typical HDN to different applied loadings. The simulation results are used to develop a quantitative yield criterion for the HDN motion under uniaxial loading. Based on this criterion together with the yield equation that can account for the non-Schmid behaviours of an isolated <1 1 1>/2 screw dislocation, the transition from primary to anomalous slips with the loading direction is predicted to be consistent with the experimental observations in many bcc metals including Mo. This work also sheds light on other experimental results such as the lack of dead-band and the displacement accompanying anomalous slip. In addition, the reason for the absence of anomalous slip in bcc iron (Fe) is found by comparison of the reaction between <1 1 1>/2 screw dislocations in Mo and Fe.