Critical stress prediction upon accurate dislocation core description. (July 2022)

• Record Type: Journal Article
• Authors: Mohammed, Ahmed Sameer Khan; Celebi, Orcun Koray; Sehitoglu, Huseyin
• Is Part Of: Acta materialia. Volume 233(2022)
• Publication Date: 2022-07
• Subjects: Dislocations -- Core width -- Critical stress -- Peierls -- Stacking fault; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2022.117989
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: 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. Graphical abstract: Image, graphical abstract