Atomistic simulations of dislocations in a model BCC multicomponent concentrated solid solution alloy

Abstract

Molecular statics and molecular dynamics simulations are presented for the structure and glide motion of a/2<111> dislocations in a randomly-distributed model-BCC Co16.67Fe36.67Ni16.67Ti30 alloy. Core structure variations along an individual dislocation line are found for a/2<111> screw and edge dislocations. One reason for the core structure variations is the local variation in composition along the dislocation line. Calculated unstable stacking fault energies on the (110) plane as a function of composition vary significantly, consistent with this assessment. Molecular dynamics simulations of the critical glide stress as a function of temperature show significant strengthening, and much shallower temperature dependence of the strengthening, as compared to pure BCC Fe as well as a reference mean-field BCC alloy material of the same lattice and elastic constants of the target alloy. Interpretation of the strength versus temperature in terms of an effective kink-pair activation model shows the random alloy to have a much larger activation energy than the mean-field alloy or BCC Fe. This is interpreted as due to the core structure variations along the dislocation line that are often unfavorable for glide in the direction of the load. The configuration of the gliding dislocation is wavy, and significant debris is left behind, demonstrating the role of local composition and core structure in creating kink pinning (super jogs) and/or deflection of the glide plane of the dislocation. This is a pre-print of the following article: Rao, S.I.; Varvenne, C.; Woodward, C.; Parthasarathy, T.A.; Miracle, D.; Curtin, W.A. Acta Materialia 2017, 125, 311--320.. The formal publication is available at http://dx

Properties of dislocation lines in crystals with strong atomic-scale disorder

“…This direct approach cuts out the need to parametrize a meso-scale model: In a concentrated solid solution the solute spacing and hence the correlation length ξ is expected to be of the order of ξ ∼ 2b only, hence a system of size 100 × 100 × 1000ξ 3 as used in our study is accessible to large-scale MD simulations. In medium-or high-entropy alloy systems for which phenomenological potentials are available, similar simulations may be performed as demonstrated by [29] for the quarternary CoFeNiTi system. The here presented method may then allow for a computationally efficient screening of the space of compositions within such an alloy system in view of establishing optimal mechanical properties, by performing serial simulations of small systems and establishing the composition dependence of the pinning length from the respective relaxed dislocation configurations.…”

Contribution of Lattice Distortion to Solid Solution Strengthening in a Series of Refractory High Entropy Alloys

“…In this case, the contribution to solid solution strengthening might not be driven by the interaction of the elastic distortion field of dislocations and the one of solute atoms but by the interaction of dislocation cores with random, local concentration fluctuations as it is suggested by Rao et al in Ref. [12]. Deviations from significant correlation might lead to the identification of (i) interesting model alloys with non-equimolar composition and/or (ii) additional contributions by short range ordering [13] as well as variations of local dislocation core structures [12] specific to certain alloys.…”

“…[12]. Deviations from significant correlation might lead to the identification of (i) interesting model alloys with non-equimolar composition and/or (ii) additional contributions by short range ordering [13] as well as variations of local dislocation core structures [12] specific to certain alloys.…”

Local-environment dependence of stacking fault energies in concentrated solid-solution alloys

“…4,8 These results unarguably indicate that the peculiar behavior of dislocations has a significant role in governing the properties of CSAs. 4,[8][9][10] As dislocation behavior is to a large extent determined by stacking fault energies (SFEs), 11 it is imperative to study the SFE properties in CSAs. A stacking fault is a planar defect in materials, and the value of the SFE represents the energy associated with interrupting the normal stacking sequence of a perfect crystal structure.…”