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Atomic scale visualizations of low-angle grain boundary mediated plasticity by coupled dislocation climb and glide in nanoporous gold

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Nano Research 2023年第2期16卷 2622-2629页

作者： Shufen Chu Junnan Jiang Xiaoran Zhao Baode Sun Pan Liu Shanghai Key Laboratory of Advanced High-temperature Materials and Precision Forming State Key Laboratory of Metal Matrix CompositesSchool of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ***,the fundamental understanding of GB-mediated deformation is still lacking because the plastic behavior of discrete ligaments involving GBs remains to be ***,we report atomic scale visualizations of coupled GB dislocation climb and glide in nanoporous gold ligaments with low-angle GBs via in situ tensile straining inside a Cs-corrected transmission electron *** zig-zag motion paths of GB dislocations are precisely determined by real-time tracking of the movements of dislocation *** concurrent climb and glide of the dislocation arrays are confined to a narrow GB region,greatly enhancing GB diffusion in the bicrystal *** findings of coupled dislocation climb and glide shine a light on the room-temperature deformation of nanoporous metals and provide a time-dependent atomic-level physical image for GB engineering.

关键词： nanoporous gold dislocation climb dislocation glide low-angle grain boundaries

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THERMODYNAMIC VARIATIONAL APPROACH FOR climb OF AN EDGE dislocation

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Acta Mechanica Solida Sinica 2009年第5期22卷 426-435页

作者： A.C.F.Cocks Department of Engineering Science University of OxfordParks RoadOxfordOX1 3PJUK

A general thermodynamic variational approach is applied to study the force on an edge dislocation, which drives the dislocation to climb. Our attention is focused on the physical mechanism responsible for dislocation climb. A dislocation in a material element climbs as a result of vacancies diffusing into or out from the dislocation core, with the dislocation acting as a source or a sink for vacancy diffusion in the material element. The basic governing equations for dislocation climb and the climb forces on the dislocation are obtained naturally as a result of the present thermodynamic variational approach.

关键词： dislocation climb driving forces variational principle

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A multi-scale algorithm for dislocation creep at elevated temperatures

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Theoretical & Applied Mechanics Letters 2021年第1期11卷 42-46页

作者： Lichao Yuan Yujie Wei State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Future Technology University of Chinese Academy of SciencesBeijing 100049China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China

dislocation creep at elevated temperatures plays an important role for plastic deformation in crystalline *** using traditional discrete dislocation dynamics(DDD)to capture this process,we often need to update the forces on N dislocations involving~N 2 *** this letter,we introduce a multi-scale algorithm to speed up the calculations by dividing a sample of interest into sub-domain grids:dislocations within a characteristic area interact following the conventional way,but their interaction with dislocations in other grids are simplified by lumping all dislocations in another grid as a super *** a multi-scale algorithm lowers the computational load to~N *** employed this algorithm to model dislocation creep in Al-Mg *** simulation leads to a power-law creep rate in consistent with experimental *** stress exponent of the power-law creep is a resultant of dislocations climb for~5 and viscous dislocations glide for~3.

关键词： Multi-scale algorithm dislocation glide dislocation climb High temperature creep dislocation dynamics

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Thermal activation parameters of V-5Cr-5Ti alloy under hot compression

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Transactions of Nonferrous Metals Society of China 2015年第8期25卷 2564-2570页

作者：李鱼飞王震宏周运洪罗超赖新春表面物理与化学重点实验室绵阳621907 中国工程物理研究院绵阳621900

In order to well understand the elementary mechanisms that govern the hot working process of a V？5Cr？5Ti alloy （mass fraction, %）, thermal activation parameters under compression were measured in a temperature range of 1373？1673 K by a Gleeble？3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy （270？300 kJ/mol） by introducing a threshold stress（σ0） variable. The typical values of physical activation volume （Vp） and strain rate sensitivity （m） are measured as （120？700）b3 and 0.075？0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V？5Cr？5Ti alloy compressed in ranges of 1373？1673 K and 0.001？1.0 s？1 is the dislocation climb by overcoming of forest dislocations.

关键词： V-5Cr-5Ti alloy hot compression thermal activation dislocation climb

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Numerical Investigations of Helical dislocations in Hydrogenated Aluminum Micropillar

Numerical Investigations of Helical Dislocations in Hydrogen...

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第十四届全国物理力学学术会议

作者：刘凤仙 LIU Zhan-Li ZHUANG Zhuo Applied Mechanics Laboratory School of Aerospace EngineeringTsinghua University

Helical dislocations are observed during the compression of a hydrogenated pure aluminum pillar at room *** is absolutely an unusual dislocation behavior at such a low temperature,but thanks to the superabundant vacancy concentration introduced along with hydrogen *** this study,a coupled glide-climb model is proposed based on three-dimensional discrete dislocation dynamics(3D-DDD) to reveal the intrinsic formation mechanism of such helical dislocation and to figure out the influence ***,a dislocation climb model is developed,which is controlled by the diffusion of the supersaturated vacancies causing by the H-trapping *** potential of this climb model is illustrated by the coarsening kinetics of prismatic ***,a coupled glide-climb model is established by incorporating dislocation climb and glide into a unified 3D-DDD framework,to investigate the formation of helical *** consistency results are obtained with the experimental data,which indicates that dislocation climb is all that needed to give rise to winding up,and the prismatic glide determines the spaces between ***,3 main influence factors to the final helical configuration are discussed:(1) the number of spirals increases linearly with the external stress and the initial dislocation configurations at a certain scope,which is very similar to the buckling of a column under axial loading where the buckling wave numbers increase as the critical load increases;(2)the formation time of the helical dislocation decreases exponentially with the vacancy concentration;(3)the vacancy concentration needed to realize the experimental configuration is predicted to be 0.02 by the coupled model,which has the same order of magnitude with the experimental data 0.01,indicating the accuracy and applicability of the coupled model in capturing the underlying *** comparing with the theoretical solution,the formation mechanism of the helical dislocation

关键词： helical dislocation micro pillar hydrogen dislocation climb vacancy concentration

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Investigations of annealing hardening in Au micropillar based on a modified discrete-continuous model

Investigations of annealing hardening in Au micropillar base...

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北京力学会第二十三届学术年会

作者： Fengxian Liu Zhan-li Liu Peng Lin Zhuo Zhuang Applied Mechanics Lab. School of Aerospace Engineering Tsinghua University

In contrast to the typical behavior at macro level, recent studies at sub-micro scale have shown that metals may harden rather than soften during high temperature annealing. In the present work, a modified three-dimensional discrete-continuous mode(DCM) is proposed to address the limitations of the local model, in which the vacancy diffusion equation is solved by the FEM. Based on this DCM model, the intrinsic mechanism of annealing hardening at sub micro scale and detailed evolution of defects during the annealing are investigated. Numerical simulation results shows that the hardening is caused by the decrease of dislocation density, which can be ascribed to two main aspects:(i) The climb of dislocation during the high temperature annealing promotes the annihilation of the dislocations, leading to a decrease in dislocation density.(ii) The jogs, nucleated during annealing due to the high temperature climb, have very weak mobility and act as obstacles to the dislocation glide motion, leading to mobile dislocation starvation and resulting in a higher flow strength level.

关键词： annealing hardening dislocation climb discrete-continuous model jogs

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