Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations

Abstract

Probing the mechanisms of defect-defect interactions at strain rates lower than 10 6 s −1 is an unresolved challenge to date to molecular dynamics (MD) techniques. Here we propose an original atomistic approach based on transition state theory and the concept of a strain-dependent effective activation barrier that is capable of simulating the kinetics of dislocation-defect interactions at virtually any strain rate, exemplified within 10 −7 to 10 7 s −1 . We apply this approach to the problem of an edge dislocation colliding with a cluster of self-interstitial atoms (SIAs) under shear deformation. Using an activation-relaxation algorithm [Kushima A, et al. (2009) J Chem Phys 130:224504], we uncover a unique strain-ratedependent trigger mechanism that allows the SIA cluster to be absorbed during the process, leading to dislocation climb. Guided by this finding, we determine the activation barrier of the trigger mechanism as a function of shear strain, and use that in a coarsegraining rate equation formulation for constructing a mechanism map in the phase space of strain rate and temperature. Our predictions of a crossover from a defect recovery at the low strainrate regime to defect absorption behavior in the high strain-rate regime are validated against our own independent, direct MD simulations at 10 5 to 10 7 s −1 . Implications of the present approach for probing molecular-level mechanisms in strain-rate regimes previously considered inaccessible to atomistic simulations are discussed.structural materials | mechanical properties | low strain rate atomistic simulation

Atomistic simulation for deforming complex alloys with application toward TWIP steel and associated physical insights

“…We note that the MAMD method follows the conventional MD procedures and cannot account for processes whose transition times exceed microseconds. Recently, a collection of algorithms including the potential energy surface sampling method has been successfully employed to assess the mechanical behavior of a nanopillar under strain rate from 1 to 10 8 s −1 (Fan et al, 2013;Yan et al, 2015;Yan and Sharma, 2016). This algorithm can be adopted by the MAMD method, which is under future investigation.…”

How thermally activated deformation starts in metallic glass

“…T he mechanical deformation of crystalline materials is governed by structural defects [1][2][3][4] , which are defined as the topological deviations from lattice periodicity. However, in amorphous materials, for example, metallic glasses, the topology of atomic connectivity varies locally and it is not obvious if the defects can be uniquely defined, even though a number of defect mechanisms of deformation have been proposed, including the concept of shear transformation zones (STZ; refs 5,6).…”

Evolution of atomic rearrangements in deformation in metallic glasses

“…Therefore, temperature and loading rate can significantly influence the evolution of the atomic rearrangement of different types of atoms. On the other hand, a similar effect of temperature and loading rate on flow stress has also been observed in crystalline solids where dislocation nucleation and mobility play important roles in plastic deformation [47][48][49]. This indicates that temperature and loading rate might have a common effect on the mechanical properties of both disordered solids and crystalline counterparts.…”