Critical stress prediction upon accurate dislocation core description

Existing approaches for friction (critical) stress determination are highly unsatisfactory because of empiricism associated with determination of dislocation “core-width” and nature of core-advance. This study, focusing on the a/2〈011〉 extended-dislocation (partials bounding a stacking-fault) in Face-Centered-Cubic (FCC) materials, rigorously derives the core-width with continuum strain-energy and atomistic misfit-energy considerations. The strain-energy is calculated using the fully-anisotropic Eshelby-Stroh formalism accommodating the inherent mixed characters of the a/6〈112〉 Shockley-partials constituting pure-edge/pure-screw a/2〈011〉 dislocations. The misfit-energy is determined from critical fault-energies of the slip-plane input to a novel misfit-model capturing the lattice structure of the slip-plane and involving the discrete Wigner-Seitz cell area at each lattice site, advancing over an 80-year old misfit-energy model that has missed the role of both concepts. For the first time in literature, the nature of motion of the a/2〈011〉 extended-dislocation's core is rigorously derived from an optimized trajectory of its total-energy. It is shown that each a/6〈112〉 partial's core moves intermittently (“zig-zag” motion), and not together, allowing the stacking-fault width to fluctuate during advance of the extended-dislocation. The critical stress is shown to involve a trajectory-dependent combination of Schmid factors for each Shockley-partial, also revealed for the first time. The proposed model is used to predict critical stress for multiple FCC materials, including a high-entropy alloy (HEA), displaying excellent agreement with experiments. The work opens future avenues for rapid reliable assessment of a multitude of compositions across varying lattice structures (e.g. hexagonal lattices), advancing over prior exponential models for critical stress which can produce errors as high as two orders of magnitude.