Geometries of edge and mixed dislocations in bcc Fe from first principles calculations

Journal Article · 26 November 2018 · Physical Review Materials

DOI: https://doi.org/10.1103/PhysRevMaterials.2.113605 · OSTI ID:1481001

Fellinger, Michael R. ^[1]; Tan, Anne Marie Z. ^[2]; Hector, Louis G. ^[3]; Trinkle, Dallas R. ^[4]

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1. Univ. of Illinois, Urbana, IL (United States). Dept. of Materials Science and Engineering; University of Illinois at Urbana-Champaign
2. Univ. of Illinois, Urbana, IL (United States). Dept. of Materials Science and Engineering; Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering
3. General Motors Global R&D Center, Warren, MI (United States)
4. Univ. of Illinois, Urbana, IL (United States). Dept. of Materials Science and Engineering

We use density functional theory (DFT) to compute the core structures of $$a_0[100](010)$$ edge, $$a_0[100](011)$$ edge, $$a_0/2[\bar{1}\bar{1}1](1\bar{1}0)$$ edge, and $$a_0/2[111](1\bar{1}0)$$ $$71^{\circ}$$ mixed dislocations in body-centered cubic (bcc) Fe. The calculations are performed using flexible boundary conditions (FBC), which effectively allow the dislocations to relax as isolated defects by coupling the DFT core to an infinite harmonic lattice through the lattice Green function (LGF). We use the LGFs of the dislocated geometries in contrast to most previous FBC-based dislocation calculations that use the LGF of the bulk crystal. The dislocation LGFs account for changes in the topology of the crystal in the core as well as local strain throughout the crystal lattice. A simple bulk-like approximation for the force constants in a dislocated geometry leads to dislocation LGFs that optimize the core structures of the $$a_0[100](010)$$ edge, $$a_0[100](011)$$ edge, and $$a_0/2[111](1\bar{1}0)$$ $$71^{\circ}$$ mixed dislocations. This approximation fails for the $$a_0/2[\bar{1}\bar{1}1](1\bar{1}0)$$ dislocation however, so in this case we derive the LGF from more accurate force constants computed using a Gaussian approximation potential. The standard deviations of the dislocation Nye tensor distributions quantify the widths of the dislocation cores. The relaxed cores are compact, and the local magnetic moments on the Fe atoms closely follow the volumetric strain distributions in the cores. We also compute the core structures of these dislocations using eight different classical interatomic potentials, and quantify symmetry differences between the cores using the Fourier coefficients of their Nye tensor distributions. Most of the core structures computed using the classical potentials agree well with the DFT results. Furthermore the DFT core geometries provide benchmarking for classical potential studies of work-hardening, as well as substitutional and interstitial sites for computing solute-dislocation interactions that serve as inputs for mesoscale models of solute strengthening and solute diffusion near dislocations.

• Research Organization: General Motors Global R&D Center, Warren, MI (United States); Univ. of Illinois, Urbana, IL (United States)
• Sponsoring Organization: National Science Foundation (NSF) (United States); USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: EE0005976
• OSTI ID: 1481001
• Journal Information: Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 11 Vol. 2; ISSN 2475-9953
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English