Investigating dislocation motion through a field of solutes with atomistic simulations and reaction rate theory

Saroukhani, Sepehr; Warner, D.H.

doi:10.1016/j.actamat.2017.02.001

Cited by 32 publications

(10 citation statements)

References 42 publications

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“…Moreover, it would be useful to study anharmonic/entropic contributions to the cross-slip rate. Entropic effects have been observed to be significant in the case of dislocation nucleation [66] and motion of a dislocation through a solute field [67]. Finally, we note that there are still only few experimentally determined values for E act of FCC cross-slip.…”

Section: Discussionmentioning

confidence: 72%

Cross-slip of long dislocations in FCC solid solutions

Nöhring

Curtin

2018

Acta Materialia

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Cross-slip of screw dislocations is a dislocation process involved in dislocation structuring, work hardening, and fatigue. Cross-slip nucleation in FCC solid solution alloys has recently been shown to be strongly influenced by local fluctuations in spatial arrangement of solutes, leading to a statistical distribution of cross-slip nucleation barriers. For cross-slip to be effective macroscopically, however, small cross-slip nuclei (~40b) must expand across the entire length of typical dislocation segments (10 2-10 3 b). Here, a model is developed to compute the relevant activation energy distribution for cross-slip in a random FCC alloy over arbitrary lengths and under non-zero Escaig and Schmid stresses. The model considers cross-slip as a random walk of successive flips of adjacent1b segments, with each flip having an energy consisting of a deterministic contribution due to constriction formation and stress effects, plus a stochastic contribution. The corresponding distribution is computed analytically from solute-dislocation and solute-solute binding energies. At zero stress, the probability of high activation energies increases with dislocation length. However, at stresses of just a few MPa, these barriers are eliminated and lower barriers are dominant. For increasing segment length, the effective energy barrier decreases according to a weak-link scaling relationship and good analytic predictions can be made using only known material properties. Overall, these results show that the effective cross-slip barrier in a random alloy is significantly lower than estimates based on average elastic and stacking fault properties of the alloy.

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Section: Discussionmentioning

confidence: 72%

Cross-slip of long dislocations in FCC solid solutions

Nöhring

Curtin

2018

Acta Materialia

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“…where T m is the melting temperature. Different studies have demonstrated the applicability of the MN compensation rule in solid mechanics [52,53,54,55,56]. The activation enthalpy and entropy barriers for each applied stress was obtained according to eqs.…”

Section: Molecular Dynamics Results 421 Uncoupled Stressesmentioning

confidence: 99%

Influence of the stress state on the cross-slip free energy barrier in Al: An atomistic investigation

et al. 2020

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The influence of the stress state on the cross-slip rate in Al was analyzed by means of molecular dynamics simulations and transition state theory. The activation energy barrier in the absence of thermal energy was determined through the nudged elastic band method while the cross-slip rates were determined using molecular dynamics simulations for different magnitudes of the Schmid stress on the cross-slip plane, and of the Escaig stresses on the cross-slip and glide planes. The enthalpy barrier and the effective attempt frequency were determined from the average rates of cross-slip obtained from the molecular dynamics simulations. It was found that the different stress states influence the cross-slip rate assuming harmonic transition state theory. Moreover, the theoretical contributions to the enthalpy barrier (configurational and due to the interaction of the applied stress with the local stress field created by the defect) were identified from the atomistic simulations while the entropic contribution to the activation energy could be estimated by the Meyer-Neldel rule. Based on these results, an analytical expression of the activation enthalpy for cross-slip in Al as a function of the different combinations of Schmid and Escaig stress states was developed and validated. This expression can be easily used in dislocation dynamics simulations to evaluate the probability of cross-slip of screw dislocation segments.

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“…A popular path-based approach is the finite temperature string method [16,[31][32][33], which is typically applied in collective variable space though in some notable cases has been applied in the full configuration space [34,35]. The method converges a discretized reaction pathway at finite temperature through the use of reflective Voronoi cells around each discretization point, before calculating the change in free energy across each cell through a population flux-based estimator.…”

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confidence: 99%

Unsupervised Calculation of Free Energy Barriers in Large Crystalline Systems

Swinburne

Marinica

2018

Phys. Rev. Lett.

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The calculation of free energy differences for thermally activated mechanisms in the solid state are routinely hindered by the inability to define a set of collective variable functions that accurately describe the mechanism under study. Even when possible, the requirement of descriptors for each mechanism under study prevents implementation of free energy calculations in the growing range of automated material simulation schemes. We provide a solution, deriving a path-based, exact expression for free energy differences in the solid state which does not require a converged reaction pathway, collective variable functions, Gram matrix evaluations, or probability flux-based estimators. The generality and efficiency of our method is demonstrated on a complex transformation of C15 interstitial defects in iron and double kink nucleation on a screw dislocation in tungsten, the latter system consisting of more than 120 000 atoms. Both cases exhibit significant anharmonicity under experimentally relevant temperatures.

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Investigating dislocation motion through a field of solutes with atomistic simulations and reaction rate theory

Cited by 32 publications

References 42 publications

Cross-slip of long dislocations in FCC solid solutions

Cross-slip of long dislocations in FCC solid solutions

Influence of the stress state on the cross-slip free energy barrier in Al: An atomistic investigation

Unsupervised Calculation of Free Energy Barriers in Large Crystalline Systems

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