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NANOSIZE EFFECT IN grain boundary migration OF COPPER

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Acta Metallurgica Sinica(English Letters) 2004年第1期17卷 11-15页

作者： L.Zhou X.Q.Wei N.G.Zhou D.G.Li School of Materials Science and Engineering Nanchang UniversityNanchang 330047ChinaSchool of Materials Science and EngineeringNanchang UniversityNanchang 330047ChinaSchool of Materials Science and EngineeringNanchang UniversityNanchang 330047ChinaCentral Iron and Steel Research InstituteBeijing 100083China

Molecular dynamics simulations of high temperature annealing of copper bicrystals have been carried out. The bicrystals have planar grain boundaries, and the gain size varies in nano range. An EAM (embedded atom method) potential of FS type is used for calculating the interatomic forces. The results show that in nanocrystalline copper, GB migration driven by inter-GB reaction can take place. A critical grain size is identified, below which the inter-GB reaction becomes strong enough to trigger GB motion, which accelerates rapidly and leads to annihilation of the grain boundaries. The critical size is found to be 16 atomic radii. A "through intermediate grain mechanism" is identified for the nano-grain boundary motion observed, which is never reported for GB migrations of conventional polycrystalline metals.

关键词： grain boundary migration nanocrystal copper

Significant annealing-induced hardening effect in nanolaminate d-nanotwinne d(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)me dium-entropy alloy by severe cold rolling

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Journal of Materials Science & Technology 2024年第3期170卷 156-166页

作者： Shuqing Yuan Hui Fu Lei Qian Chi Fai Cheung Xu-Sheng Yang State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems EngineeringThe Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen 518060China

Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)medium-entropy alloy with an average lamellae thickness of∼20 nm embedded by thinner nanotwins was fabricated by severe cold rolling to achieve superior thermal stability.Compared with the conventional nanotwinned CrCoNi with nanotwins inside ultra-fined grains,the hier-archical nanolaminated-nanotwinned(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8) exhibits a significant annealing-induced hard-ening effect,i.e.,hardness increasing from∼250 HV in the original specimen to∼500 HV in the cold-rolled status and finally∼630 HV after annealing at 600℃for 1 h.Detailed microstructure characterizations reveal that the reduced dislocation density and formation of L1_(2)ordered domain are mainly responsible for such hardening effect,which is facilitated by the effectively suppressed coarsening with annealing temperature,i.e.,slow detwinning process and well-retained low-angle nanolamellar structure.The coarsening mechanisms from the cold-rolled nanolamellae to the fully recrystallized micro-equiaxed structures under the annealing temperatures ranging from 400 to 800℃ were also elucidated by atomic observations.

关键词： Annealing-induced hardening Thermal stability Nanolaminated-nanotwinned structure CrCoNi Detwinning grain boundary migration

Shock-induced migration of asymmetry tilt grain boundary in iron bicrystal: A case study of Σ3 [110]

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Chinese Physics B 2019年第12期28卷 273-279页

作者：张学阳王昆陈军胡望宇祝文军肖时芳邓辉球蔡孟秋 Department of Applied Physics School of Physics and ElectronicsHunan UniversityChangsha 410082China Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China Center for Applied Physics and Technology Peking UniversityBeijing 100087China College of Materials Science and Engineering Hunan UniversityChangsha 410082China National Key Laboratory of Shock Wave and Detonation Physics Institute of Fluid PhysicsMianyang 621900China

Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals.In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry tilt grain boundary(ATGB) under shock-loading is performed. We find that the shock response of asymmetric grain boundaries is quite different from that of symmetric grain boundaries. Especially, our simulation proves that shock can induce migration of asymmetric grain boundary in iron. We also find that the shape and local structure of grain boundary(GB) would not be changed during shock-induced migration of Σ3 [110] ATGB, while the phase transformation near the GB could affect migration of GB. The most important discovery is that the shock-induced shear stress difference between two sides of GB is the key factor leading to GB migration. Our simulation involves a variety of piston velocities, and the migration of GB seems to be less sensitive to the piston velocity. Finally, the kinetics of GB migration at lattice level is discussed. Our work firstly reports the simulation of shock-induced grain boundary migration in iron. It is of great significance to the theory of GB migration and material engineering.

关键词： shock-loading grain boundary migration iron phase transition

Coordinated grain boundary deformation governed nanograin annihilation in shear cycling

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Journal of Materials Science & Technology 2021年第27期86卷 180-191页

作者： Yingbin Chen Qishan Huang Qi Zhu Kexing Song Yanjun Zhou Haofei Zhou Jiangwei Wang Center of Electron Microscopy and State Key Laboratory of Silicon Materials School of Materials Science and EngineeringZhejiang UniversityHangzhou310027PR China Center for X-Mechanics Department of Engineering MechanicsZhejiang UniversityHangzhou310027PR China School of Materials Science&Engineering Henan University of Science and TechnologyLuoyang471023PR China

grain growth and shrinkage are essential to the thermal and mechanical stability of nanocrystalline metals,which are assumed to be governed by the coordinated deformation between neighboring grain boundaries(GBs)in the nanosized grains.However,the dynamics of such coordination has rarely been reported,especially in experiments.In this work,we systematically investigate the atomistic mechanism of coordinated GB deformation during grain shrinkage in an Au nanocrystal film through combined stateof-the-art in situ shear testing and atomistic simulations.We demonstrate that an embedded nanograin experiences shrinkage and eventually annihilation during a typical shear loading cycle.The continuous grain shrinkage is accommodated by the coordinated evolution of the surrounding GB network via dislocation-mediated migration,while the final grain annihilation proceeds through the sequential dislocation-annihilation-induced grain rotation and merging of opposite GBs.Both experiments and simulations show that stress distribution and GB structure play important roles in the coordinated deformation of different GBs and control the grain shrinkage/annihilation under shear loading.Our findings establish a mechanistic relation between coordinated GB deformation and grain shrinkage,which reveals a general deformation phenomenon in nanocrystalline metals and enriches our understanding on the atomistic origin of structural stability in nanocrystalline metals under mechanical loading.

关键词： Nanocrystalline metals grain shrinkage and annihilation grain boundary migration grain rotation Coordinated deformation

Morphology and orientation evolution of Cu_(6)Sn_(5)grains on(001)Cu and(011)Cu single crystal substrates under temperature gradient

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Journal of Materials Science & Technology 2021年第36期95卷 29-39页

作者： Yuanyuan Qiao Xiaoying Liu Ning Zhao Lawrence C M Wu Chunying Liu Haitao Ma School of Materials Science and Engineering Dalian University of TechnologyDalian 116024China Department of Materials Science and Engineering City University of Hong KongHong Kong Special Administrative RegionChina

The morphology and orientation evolution of Cu_(6)Sn_(5)grains formed on(001)Cu and(011)Cu single crystal substrates under temperature gradient(TG)were investigated.The initial orientated prism-type Cu_(6)Sn_(5)grains transformed to non-orientated scallop-type after isothermal reflow.However,the Cu_(6)Sn_(5)grains with strong texture were revealed on cold end single crystal Cu substrates by imposing TG.The Cu_(6)Sn_(5)grains on(001)Cu grew along their c-axis parallel to the substrate and finally merged into one grain to form a fully IMC joint,while those on(011)Cu presented a strong texture and merged into a few dominant Cu_(6)Sn_(5)grains showing about 30°angle with the substrate.The merging between neighboring Cu_(6)Sn_(5)grain pair was attributed to the rapid grain growth and grain boundary migration.Accordingly,a model was put forward to describe the merging process.The different morphology and orientation evolutions of the Cu_(6)Sn_(5)grains on single crystal and polycrystal Cu substrates were revealed based on crystallographic relationship and Cu flux.The method for controlling the morphology and orientation of Cu_(6)Sn_(5)grains is really benefitial to solve the reliability problems caused by anisotropy in 3 D packaging.

关键词： 3D packaging Single crystal Cu Temperature gradient Orientation Disregistry grain boundary migration

A general mechanism of grain growth-Ⅰ.Theory

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Journal of Materiomics 2021年第5期7卷 1007-1013页

作者： Jianfeng Hu Xianhao Wang Junzhan Zhang Jun Luo Zhijun Zhang Zhijian Shen School of Materials Science and Engineering Shanghai UniversityShanghai200444China Carl Zeiss Co. Shanghai60 Meiyue RoadShanghai200131China College of Materials and Mineral Resources Xi’an University of Architecture and Technology13 Yanta RoadXi’an710055China Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm UniversityS-10691StockholmSweden Materials Genome Institute Shanghai UniversityShanghai200444China

The behaviors of grain growth dominate the formation of the microstructure inside polycrystalline materials and thus strongly influence their practical performances.However,grain growth behaviors still remain ambiguous and thus lack a mathematical formula to describe the general evolution despite decades of efforts.Here,we propose a new migration model of grain boundary(GB)and further derive a mathematical expression to depict the general evolution of grain growth in the cellular structures.The expression incorporates the variables influencing growth rate(e.g.GB features,grain size and local grain size distribution)and thus reveals how the normal,abnormal and stagnant behaviors of grain growth occur in polycrystalline systems.In addition,our model correlates quantitatively GB roughening transition with grain growth behavior.The general growth theory may provide new insights into the GB thermodynamics and kinetics during the cellular structure evolution.

关键词： grain boundary migration grain growth Roughening transition Abnormal grain growth