Slip system interactions in BCC single crystals: System deactivation and segregation

In single crystal plasticity, latent hardening between the different slip systems, coming from the interaction of dislocations, strongly influences the slip system activity under prescribed deformation. Both the deactivation of redundant systems and the potential segregation of the remaining ones in separated zones set up in a way that minimizes the work expended and thus tends to eliminate the strongest interactions: these phenomena can be analyzed as unstable perturbations of the initial loading path activating all systems favorably oriented towards the loading orientation. This question, investigated in previous papers for FCC copper by comparing crystal plasticity computation to linear stability analysis (Dequiedt et al., 2015; Dequiedt, 2018), is pursued in this work for the case of BCC crystals loaded along axes of symmetry of the crystal lattice. In the athermal regime, the potential activation of {112} systems in addition to {110} systems increases the number of systems available to accommodate the deformation and the possibilities to eliminate strong interactions; similar trends as for FCC crystals are observed, i.e. the role played by the very strong collinear interaction in the first place and the influence of hard junctions in the second place. On the contrary, in the thermal activation regime, the effect of latent hardening is alleviated by the high shearing rate sensitivity which tends to favor the simultaneous activation of numerous systems regardless of their mutual hardening: symmetry breaking evolution linked with system deactivation and segregation are thus strongly penalized, especially when only junctions are involved.