Atomistic simulations of dislocations in a model BCC multicomponent concentrated solid solution alloy

Molecular statics and molecular dynamics simulations are presented for the structure and glide motion of a/2(111) dislocations in a randomly-distributed model-BCC Co16.67Fe36.67Ni16.67Ti30 alloy. Core structure variations along an individual dislocation line are found for a/2(111) screw and edge dislocations. One reason for the core structure variations is the local variation in composition along the dislocation line. Calculated unstable stacking fault energies on the (110) plane as a function of composition vary significantly, consistent with this assessment. Molecular dynamics simulations of the critical glide stress as a function of temperature show significant strengthening, and much shallower temperature dependence of the strengthening, as compared to pure BCC Fe as well as a reference mean-field BCC alloy material of the same overall composition, lattice and elastic constants as the target alloy. Interpretation of the strength versus temperature in terms of an effective kink-pair activation model shows the random alloy to have a much larger activation energy than the mean-field alloy or BCC Fe. This is interpreted as due to the core structure variations along the dislocation line that are often unfavorable for glide in the direction of the load. The configuration of the gliding dislocation is wavy, and significant debris is left behind, demonstrating the role of local composition and core structure in creating kink pinning (super jogs) and/or deflection of the glide plane of the dislocation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.