Multiphase field modeling of grain boundary migration mediated by emergent disconnections

Abstract

Knowledge about grain boundary migration is a prerequisite for understanding and ultimately modulating the properties of polycrystalline materials. Evidence from experiments and molecular dynamics (MD) simulations suggests that the formation and motion of disconnections is a mechanism for grain boundary migration. Here, grain boundary migration is modeled using a multiphase field model based on the principle of minimum dissipation potential with nonconvex boundary energy, along with a stochastic model for thermal nucleation of disconnection pairs. In this model, disconnections arise spontaneously in the presence of an elastic driving force, and that their motion mediates boundary migration. The effect is due to the fact that the formation of the disconnections pairs results in a stress concentration, causing the elastic driving force to exceed the threshold value and driving the propagation of the disconnection along the interface. The model is applied to study the propagation/annihilation of single disconnection pairs, the relaxation of a perturbed interface, and shear coupling at various temperatures. The results are consistent with the current understanding of disconnections, and capture the effect of thermal softening.

Polycrystal plasticity with grain boundary evolution: a numerically efficient dislocation-based diffuse-interface model

“…It is true that many other models for GB migration exist, but a comparison of numerical efficiency is not fair unless the models being compared include similar physics. To this end, it is appropriate to compare our work with some dislocation-based models such as Zhang and Xiang (2018) and Zhang and Xiang (2020), and disconnection-based models such as Runnels and Agrawal (2020) and Gokuli and Runnels (2021). However, as those models are still under active development and are not formulated for numerical efficiency, further comparison is not pursued here.…”

“…In this paper, we also discuss the limitations of the dislocations-based framework of Admal et al (2018). In this regard, we take note of the recent development of a new class of shearcoupled GB models (Thomas et al 2017, Gokuli and Runnels 2021, Runnels and Agrawal 2020 developed in the backdrop of overwhelming evidence from atomic scale simulations or experiments (Zhu et al 2019, Merkle et al 2002, Rajabzadeh et al 2013a, 2013b, Mompiou et al 2015 that disconnections are the primary carriers of GB plasticity. Disconnection-based continuum models, in which GB motion is dictated by the evolution of continuum disconnections, offer unique advantages compared to our dislocation-based framework.…”