Grain boundary (GB) diffusion in polycrystalline materials is a physical phenomenon of great fundamental interest and practical significance. Although the accelerated ("short circuit") atomic transport along GBs has been known for decades, the current atomic-level understanding of GB diffusion remains poor. Experiments can measure numerical values of GB diffusion coefficients but provide little information about the underlying mechanisms. Previous atomistic simulations focused on relatively low temperatures when the GB structure is ordered or relatively high temperatures when it is highly disordered. Here, we report on molecular dynamics simulations of GB diffusion at intermediate temperatures, which are most relevant to applications. One of the surprising results of this work is the observation of strongly intermittent GB diffusion behavior and its strong system-size dependence unseen in previous work. We demonstrate that both effects originate from an intermittent, avalanche-type generation of point defects causing spontaneous bursts of GB diffusivity mediated by highly cooperative atomic rearrangements. We identify the length and time scales of the avalanches and link their formation to the dynamic heterogeneity phenomenon in partially disordered systems. Our findings have significant implications for future computer modeling of GB diffusion and mass transport in nano-scale materials.
From metallic glasses to nanocrystals: Molecular dynamics simulations on the crossover from glass-like to grain-boundary-mediated deformation behaviour
Elastically-mediated interactions between grain boundaries and precipitates in two-phase coherent solids
本文用解析和数值方法研究了在失配应变存在下两相共格固体中晶界和第二相沉淀物之间的相互作用。我们的数值研究使用振幅方程描述的成分和应力的相互作用[R。Spatschek和A. Karma，Phys. Rev. B { \bf 81}，214201（2010）]以及分别对应于表现出各向同性和各向异性弹性性质的二维六边形和三维BCC晶体结构的自由能。我们考虑两个实验动机的几何形状，其中（i）层状沉淀物成核沿平面晶界内的沉淀物为中心，和（ii）一个圆形的沉淀物成核内的晶粒在一个有限的距离，最初的平面晶界。对于第一种几何形状，我们发现，晶界变得形态不稳定，由于长期的弹性相互作用之间的晶界和组成域边界，和剪切耦合晶界运动的组合。我们通过扩展最近进行的线性稳定性分析来解析地描述这种不稳定性[P. - A. Geslin，Y. C. Xu，和A. Karma，Phys. Rev. Lett. { \bf 114}，105501（2015）]中描述的弹性各向异性的更一般情况。分析预测，弹性各向异性阻碍，但不抑制不稳定。模拟还表明，在一个发达的非线性政权，这种不稳定性可能会导致小角度晶界的破裂时，失配应变超过一个阈值，取决于晶界取向差。对于第二种几何形状，模拟表明，初始平面晶界和相邻的圆形沉淀物之间的弹性相互作用导致沉淀物迁移到晶界并锚定在晶界处。
A Mesoscale Model for Interface-Mediated Plasticity: Investigation of Ductile and Brittle Fracture
City University of Hong Kong（香港城市大学）；University of California, Los Angeles（加州大学洛杉矶分校）；The University of Hong Kong（香港大学）；University of Birmingham（伯明翰大学）
Nanoscale Strain Evolution and Grain Boundary-Mediated Defect Sink Behavior in Irradiated SiC: Insights from N-PED and DFT
Czech Technical University in Prague（布拉格捷克理工大学）；Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Southwest University and Technology（西南科技大学）；Helmholtz–Zentrum Dresden–Rossendorf, Institute of Ion Beam Physics and Materials Research（德累斯顿罗森多夫亥姆霍兹中心离子束物理与材料研究所）；Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences（中国科学院上海微系统与信息技术研究所）；Nuclear Physics Institute of the Czech Academy of Sciences（捷克科学院核物理研究所）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）；University of Southampton（南安普顿大学）
本文利用 N-PED 和 DFT 揭示辐照 SiC 中晶界作为缺陷汇引发应变放大与贫泡区应变释放的机制，为晶界工程提升耐辐射性能提供依据。
Deconvoluting Mechanisms of Radiation-Induced Grain Boundary Segregation in Dilute Ni-X (X = Fe, Cr, Mn) Alloys via Ion Irradiation and Phase-field Modeling
Idaho National Laboratory（爱达荷国家实验室）；Texas A&M University（德克萨斯农工大学）
Phonon-Mediated Thermal Transport in Nanocrystalline Silicon Using Machine-Learning Interatomic Potentials
International Iberian Nanotechnology Laboratory (INL)（伊比利亚纳米技术国际实验室）；Universitat de Barcelona (UB)（巴塞罗那大学）；Institute of Nanoscience and Nanotechnology (IN2UB)（纳米科学与技术研究所）；Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学技术研究所（ICN2）, 西班牙国家研究委员会和巴塞罗那智能科技学院）；Nanomaterials and Nanotechnology Research Center (CINN-CSIC), Universidad de Oviedo (UO)（纳米材料与纳米技术研究中心（CINN-CSIC）, 奥维耶多大学）
Grain boundaries amplify local chemical ordering in complex concentrated alloys
University of California, Irvine（加州大学尔湾分校）；Hopkins Extreme Materials Institute, Johns Hopkins University（约翰斯·霍普金斯大学霍普金斯极端材料研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）
