Molecular Dynamics Simulations of Dislocation Nucleation from a Pristine and Damaged Grain Boundary in Nickel and Quantification of Associated Activation Energy Parameters

Abstract

AbstractGrain boundaries are important microstructural features in polycrystalline materials that impact their deformation and failure behavior at the macroscopic scale. Thus, we perform atomistic simulations at the nanoscale along with nudged elastic band calculations to quantify activation parameters for dislocation nucleation from a grain boundary. Since \(\sum \)3 grain boundaries are most common in polycrystalline metals and alloys of face-cantered cubic structure, we choose \(\sum \)3 twin boundary in bicrystal Ni as a model system for this purpose. We also introduce a pre-existing defect (a void) at the grain boundary and contrast the activation parameters for partial dislocation nucleation from pristine as well as damaged grain boundary in the material. We find that the activation energy as well as kinetic parameters for dislocation nucleation are different for pristine and damaged grain boundary. This highlights a change in the underlying kinetics of the deformation process when a damaged grain boundary is present in the material. Consequently, this approach can be generalized to determine kinetic parameters for other thermally activated grain boundary-dominated deformation or failure processes in metallic polycrystals like grain boundary sliding at a higher temperature, intergranular crack growth, etc. It can, therefore, provide direct numerical inputs to the flow rules of phenomenological crystal plasticity-based finite element models that explicitly take into account the grain boundary effects on plasticity and damage behavior of the material at the continuum scale.KeywordsMolecular dynamicsPlasticityGrain boundaryDamage