Dislocation core field.II. Screw dislocation in iron

Abstract

The dislocation core field, which comes in addition to the Volterra elastic field, is studied for the 111 screw dislocation in alpha-iron. This core field, evidenced and characterized using ab initio calculations, corresponds to a biaxial dilatation, which we modeled within the anisotropic linear elasticity. We show that this core field needs to be considered when extracting quantitative information from atomistic simulations, such as dislocation core energies. Finally, we look at how dislocation properties are modified by this core field, by studying the interaction between two dislocations composing a dipole, as well as the interaction of a screw dislocation with a carbon atom.

First-principles prediction of kink-pair activation enthalpy on screw dislocations in bcc transition metals: V, Nb, Ta, Mo, W, and Fe

“…Intense investigations are lead on these dislocations (see for example Refs. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]), the main issue being to derive the dislocation mobility law from the atomic scale [18]. Among the different computational studies, calculations based on density-functional theory (DFT) have established some important features that were previously matter of debate in bcc transition metals, such as the nondegenerate dislocation core structure [6,10,17], the {110} glide plane [9], and the single-hump Peierls barrier [10,17,[19][20][21].…”

“…However, the main drawback of DFT-based methods applied to extended defects such as dislocations is the limited number of atoms that can be considered in the simulation cell, typically a few hundred. These cell sizes are sufficient to study straight dislocations perfectly aligned with their b = a 0 /2 111 Burgers vector, where a 0 is the equilibrium lattice parameter, because the translational invariance along the dislocation line allows to reduce the cell size in this direction to a slab of length b = |b| = a 0 √ 3/2 using periodic boundary conditions [9][10][11][12]. At finite temperatures [22], however, the motion of screw dislocations proceeds through the formation of kink pairs, thereby breaking the translational invariance along the dislocation line.…”

Solute strengthening in random alloys

“…New alloy design can therefore be undertaken based on the full version of the strengthening model of Eqs. (8), (12) and (14).…”

“…This interaction energy U el (x i , y j ) = −p(x i , y j )∆V , also referred to as the first order "size" interaction [12], is equal to the work done on the dislocation pressure field by the expansion or contraction of the material upon addition of the misfitting solute atom. This mechanical interaction energy can be generalized to include the interaction energy between deviatoric misfit strains and the deviatoric dislocation stress field (the first order "shape" interaction), which is typically important for interstitial solutes [13,14,15]. For simplicity here, we focus on misfit volumetric strains that are appropriate for substitutional solutes in cubic matrices [16,17].…”

“…For simplicity here, we focus on misfit volumetric strains that are appropriate for substitutional solutes in cubic matrices [16,17]. The elastic interactions are long-ranged, since the dislocation stress field decays only as 1/r with distance r from the center of the dislocation, and give a quantitative description of the solute/dislocation interaction away from immediate dislocation core region [13,14,15,16,17,18].…”