Finite-temperature screw dislocation core structures and dynamics in α-titanium

Anwen Liu, Tongqi Wen, Jian Han & David J. Srolovitz 

npj Computational Materials  9: 228 (2023). Published: 21 December 2023

编辑概述

由香港城市大学材料科学与工程系的Jian Han教授以及香港大学机械工程系的David J. Srolovitz教授领导的研究团队，聚焦于位错核心结构相关的位错固有属性研究，开发了一套结合分子动力学（MD）与动力学蒙特卡洛（kMC）方法的多尺度仿真技术。为了更深入地研究核心效应，同时避免扭结动力学复杂特性的影响（例如，这些特性会随局部位错曲率、结点以及与其他位错的相互作用等因素而发生明显变化），研究中有意忽略了在长位错运动中至关重要的错节作用。研究团队探索了温度作为影响因素时，α-钛中短〈a〉螺旋位错段的核心结构效应。实验结果揭示，HCP结构Ti的屈服强度主要受螺旋位错引起的晶格摩擦力控制，同时发现边缘位错具有极高的移动性。在研究中，使用了基于机器学习势能模型的分子动力学模拟来研究螺旋位错核心结构，以及核心结构之间的转变，对位错运动进行了统计分析，并确定了描述螺旋位错运动的动力学参数，如迁移过程中的自由能势垒。随后，研究团队结合这些精确的量子力学分子动力学模拟参数，运用动力学蒙特卡洛方法模拟了钛中螺旋位错的运动。研究还考察了温度和加载方向对于位错核心转变和位错移动性的具体影响。这些成果对于理解和预测具有复杂晶体结构金属中非阿伦尼乌斯螺旋位错的非常规移动性提供了重要的科学基础。

Editorial Summary

Multiscale Simulation Method Combining MD and kMC: Unveiling the Dislocation Glide Mechanism in Metal Plasticity

The key to plastic deformation in crystalline metals lies in dislocation glide, but the path of dislocation movement does not always follow the predictions of maximum shear stress theory. This phenomenon is closely related to the glide resistance between different slip planes and the structure of dislocation cores, which are often temperature-dependent. The challenge in current research is the lack of a direct quantitative link between dislocation core structure and dynamics. To address this gap, researchers have developed a new multiscale simulation method, which combines precise atomic-scale descriptions to predict the temperature dependence and dynamic behavior of dislocation core structures in α-titanium.

A team lead by Prof. Jian Han from Department of Materials Science and Engineering, City University of Hong Kong and Prof. David J. Srolovitz from Department of Mechanical Engineering, The University of Hong Kong, focused on the study of intrinsic properties related to dislocation core structures. They have developed a set of multiscale simulation techniques that integrate Molecular Dynamics (MD) and Kinetic Monte Carlo (kMC) methods. The admittedly important roles played by dislocation kinks in the motion of long dislocations are omitted here in order to provide a thorough examination of core effects without the complicated features of kink dynamics (which vary dramatically with, e.g., local dislocation curvature, junctions and interactions with other dislocations). The effects of core structure of short 〈a〉 screw dislocation segments in α-Ti based on the DP for Ti as a function of temperature are investigated. Experimental observations show that the edge dislocations are highly mobile and the yield strength of HCP Ti is governed by screw dislocation lattice friction. The authors report the results of MD simulations (based on machine learning potentials of quantum mechanical accuracy) of screw dislocation core structures, transitions between different core structures, statistical analysis of dislocation motion, and the determination of the kinetic parameters (i.e., free energy barriers associated with migration, core structure transitions, ...) describing screw dislocation motion. The authors then perform kinetic Monte Carlo simulations of screw dislocation motion in Ti incorporating these quantum mechanically accurate MD simulation parameters. The authors examine the effect of both temperature and loading direction on dislocation core transitions and dislocation mobility. The results provide the basis for understanding non-Arrhenius screw dislocation mobility in metals with complex crystal structures.