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Journal of Materials Science & Technology 2020年第6期41卷 127-138页

作者： Y.X.Lai W.Fan M.J.Yin C.L.Wu J.H.Chen center for High-Resolution electron microscopy College of Materials Science&EngineeringHunan UniversityChangsha 410082China electron microscopy center Shenzhen UniversityShenzhen 518060China

In the slightly deformed Al-Mg-Si alloys,dislocation-induced precipitates are frequently observed,and they usually line up,forming sophisticated precipitation *** atomic-resolution electron microscopy in association with hardness measurements,we systematically investigated these precipitates in relation to the age-hardening responses of the *** study reveals that the majority of dislocation-induced complex precipitates are actually short-range ordered while long-range disordered polycrystalline precipitates and multiphase composite precipitates,including polycrystalline U2 precipitates,B’/U2,B’-2/U2,B’/B’-2/U2 and’/U2 composite *** is suggested that the formation of these complex precipitates is mainly owing to a high nucleation rate and rapid growth of different precipitate phases parallel to the associated dislocation *** dislocation-induced precipitates consume more Mg than Si from the matrix and have a high formation kinetics,they will have different impacts on the matrix precipitation in different types of Al-Mg-Si *** results further demonstrate that for the"normally-β"-hardened"alloy,their formation leads to a coarser precipitate microstructure in the matrix,whereas for the"normally-β’-hardened"alloy,their formation reverses the precipitation pathway in the matrix,resulting in a reduced age-hardening potential of the former alloy and an improved age-hardening potential of the latter alloy.

关键词： Al-Mg-Si alloys Precipitation Dislocation Age-hardening electron microscopy

Structure and Growth Mechanism of V/Ag Multilayers with Different Periodic Thickness Fabricated by Magnetron Sputtering Deposition

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Journal of Materials Science & Technology 2014年第10期30卷 1012-1019页

作者： Hongxiu Zhang Feng Ren Mengqing Hong Xiangheng Xiao Guangxu Cai Changzhong Jiang School of Physics and Technology Center for Ion Beam Applicationand Center for Electron MicroscopyWuhan University

V/Ag multilayers with different periodic thicknesses were fabricated by magnetron sputtering deposition. The columnar structure and the orientation relationship of the multilayers were investigated by transmission electron microscopy, high resolution transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. It was found that the multilayered structure became flatter as increasing individual layer thickness from 2 to 6 nm, and then became waved as the individual layer thickness increases to 8 nm. At the beginning of the growth, the morphology of the multilayers with small periodic thickness was influenced mainly by thermodynamic instabilities, and the morphology of the multilayers with larger periodic thickness was mainly influenced mainly by the columnar growth of V. When the waved interfaces were formed, the continuum growth of the multilayers was also influenced by the shadowing effect and the finite atomic size effect. All of these factors resulted in the columnar structure of the multilayers. Multilayers with small periodic thickness presented strong orientation relationship. Nano-hardness tests indicated that multilayers with flat sublayer morphology and clear interfaces exhibited larger hardness.

关键词： Multilayers Interfaces Columnar structure Transmission electron microscopy

Complex Precipitation Sequences of Al-Cu-Li-(Mg)Alloys Characterized in Relation to Thermal Ageing Processes

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Acta Metallurgica Sinica(English Letters) 2016年第1期29卷 94-103页

作者： Zhen Gao Jiang-Hua Chen Shi-Yun Duan Xiu-Bo Yang Cui-Lan Wu center for High-Resolution electron microscopy College of Materials Science and EngineeringHunan University

The A1-Cu-Li-（Mg） alloy is a high-performance lightweight material strengthened by complex coexisting precipitates that form in the alloy upon thermal ageing. Using high-resolution （scanning） transmission electron microscopy in association with first-principles energy calculations, we systematically studied the complex coexisting precipitates in the alloys and correlated their precipitation sequences with thermal ageing processes applied. The principal results are the following：（1） eight types of precipitates can be observed in the alloy; （2） of these precipitates, the Tl-phase is most stable. The S-phase precipitates with segregated Li atoms at their interfacial edges are unexpectedly more stable than the a-phase; （3） the Tl-phase has a characteristic precursor that plays the key role in its nucleation and growth.

关键词： AI-Cu-Li alloy electron microscopy Ageing Precipitation Strength

Optimal design of self-propagating high temperature one-dimensional nano-SnO_2 synthesis

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Acta Metallurgica Sinica(English Letters) 2011年第4期24卷 321-325页

作者： Nian LIU Guodonq ZHANG Department of Materials Engineering and center for electron microscopy Wuhan UniversityWuhan 430072 China

The success in synthesizing high purity SnO2 nanobelts via self-propagating high tem- perature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction system at 2848 K and SnO2 nanobelts yield was identified. The most appropriate formula for this self-propagating high tempera- ture synthesis method is turned out to be composed of Sn powder and thermite with weight ratio of 1：1.

关键词： Optimal design Self-propagating high temperature synthesis Nano-Sn02

Preparation of size controllable copper nanocrystals for nonvolatile memory applications

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Chinese Physics B 2010年第10期19卷 593-596页

作者：王利孙红芳周惠华朱静 Beijing National center for electron microscopy Department of Materials Science and Engineering Tsinghua University

A method of fabricating Cu nanocrystals embedded in SiO2 dielectric film for nonvolatile memory applications by magnetron sputtering is introduced in this paper. The average size and distribution density of Cu nanocrystal grains are controlled by adjusting experimental parameters. The relationship between nanocrystal floating gate micro-structure and its charge storage capability is also discussed theoretically.

关键词： nanocrystal grain nonvolatile memory Coulomb blockade effect magnetron sputtering

An electron microscopy Study of Vein-like Grain Boundary Microstructure in Nitrocarburized Low Carbon Steels

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Journal of Materials Science & Technology 2013年第7期29卷 669-672页

作者： Wanglin Chen Cuilan Wu Jianghua Chen Aigui He center of High Resolution electron microscopy College of Materials Science and EngineeringHunan University

The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.

关键词： Nitrocarburizing Grain boundary γ'-Fe4(C,N) e-Nitrocarbide

In-situ evaluation for corrosion process at fusion boundary of stainless steel strip overlay joints in H2S containing solution

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中国有色金属学会会刊：英文版 2004年第z1期14卷 413-419页

作者： ZOU Yang PAN Chun-xu FU Qiang Department of Physics & center for electron microscopy Wuhan University Wuhan 430063 China Department of Physics & Center for Electron Microscopy Wuhan University Wuhan 430063 China Department of Physics & Center for Nano-Science and Technology Wuhan University Wuhan 430063 China

The present work studied the corrosion properties around the fusion boundaries of 2.25Cr-1Mo steel with stainless steel strip overlay joints under as welded condition and after post-weld heat treatment (PWHT) in H2 S containing solution (NACE TM-01-77 standard) with different time. An in-situ observation method was introduced for evaluating corrosive progress in the fusion boundary in H2 S containing solution, that is, the samples were marked firstly at the boundary and then treated in the solution for variant time. Each time after the corrosion treatment, the observations were kept to focus at the same marked area by using scanning electron microscopy (SEM) to observe the corrosion progress. The results reveal that the fusion boundary is the worst region for corrosion resistance when comparing with other boundaries, and a broad fusion boundary has a stronger resistance for "hydrogen induced disbonding" than a narrow one.

关键词： dissimilar steel welding fusion boundary H2S corrosion post-weld heat treatment

Atomic-scale roles of Zn element in age-hardened AlMgSiZn alloys

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Journal of Materials Science & Technology 2021年第11期70卷 105-112页

作者： N.N.Jiao Y.X.Lai S.L.Chen P.Gao J.H.Chen center for High-Resolution electron microscopy College of Materials Science&EngineeringHunan UniversityChangsha410082China electron microscopy Laboratory and International center for Quantum Materials School of PhysicsPeking UniversityBeijing100871China

Adding alloying elements to improve the performances or the manufacturing processes of Al-Mg-Si alloys has long been a serious issue in developing advanced automotive aluminum *** Zn element,among those promising ones,has demonstrated positive alloying effects on Al-Mg-Si ***,the atomic-scale roles of Zn in an age-hardened Al-Mg-Si-Zn alloy have not been adequately *** atomic-resolution electron microscopy,here we report the precise locations of Zn elements in all hardening precipitates involved and their alloying mechanism at the atomic scale when alloying the *** results show that Zn atoms enter all the major hardening phases to occupy specific featured atomic sites of the original elements,*** Si1 and Mg2 sites in theβ’-2 phase,and modify their crystal structures,interfacial structures and morphologies in characteristic *** is revealed that for theβ’-phase,Zn atoms occupy unique atomic sites,whereas for other phases,they demonstrate similar behaviors as other additive alloying elements such as Ag and Cu do.

关键词： Al-Mg-Si alloy Zn addition Precipitate electron microscopy

Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal–Mechanical Treatments

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Acta Metallurgica Sinica(English Letters) 2022年第2期35卷 275-284页

作者： L.M.Liu Y.X.Lai C.L.Wu Z.Zhang J.H.Chen center for High-Resolution electron microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

This study investigates the microstructure and local corrosion behavior of an Al-Mg-Si-Cu alloy,which has been subjected to cold-rolling with different deformation strain ratios(DSRs)and followed by artificial *** corrosion tests show that peak-aged samples with a small DSR(5-10%)are sensitive to inter-granular corrosion(IGC)along both the normal and rolling *** the DSR increases to medium strength(20-40%),IGC sensitivity decreases along both directions and corrosion propagates *** the DSR is 60-80%,IGC sensitivity along the normal direction continues to decrease,but increases along the rolling direction,indicating pronounced corrosion *** characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion *** increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.

关键词： Al alloys Local corrosion Anisotropy Transmission electron microscopy(TEM) electron backscattering diffraction(EBSD)

Dislocation-Induced Precipitation and Its Strengthening of Al–Cu–Li–Mg Alloys with High Mg

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Acta Metallurgica Sinica(English Letters) 2021年第5期34卷 597-605页

作者： Xiangpeng Gong Shifang Luo Shiyong Li Cuilan Wu center for High-Resolution electron microscopy College of Materials Science and EngineeringHunan UniversityChangsha410082China

Generally, the good combination of pre-deformation and aging can improve the mechanical strength of the Al–Cu–Li–Mg alloys. However, the effects of pre-deformation on competitive precipitation relationship and precipitation strengthening have not been clarified in detail in Al–Cu–Li–Mg alloys with high Mg. In the present study, the effects of pre-deformation level on the microstructure and mechanical properties of an Al–2.95 Cu–1.55 Li–0.57 Mg–0.18 Zr alloy have been investigated. It is found that the introduction of dislocation by 5% pre-deformation can facilitate the precipitation of new successive composite precipitates and T _1 precipitates along the sub-grain boundaries or dislocations and inhibit the precipitation of dispersive GPB zones which is the main precipitates of the alloys without pre-deformation. The introduction of 5% pre-deformation can enhance the mechanical properties considerably. When the pre-deformation level increases from 5 to 15%, the number density of the successive composite precipitates and T _1 precipitates increases, and the aspect ratio of T _1 precipitates decreases. The decrease in T _1 precipitate aspect ratio and the increment of the successive composite precipitates result in the reduction in precipitation strengthening. Therefore, the increase in pre-deformation level from 5 to 15% does not further improve the mechanical properties of the alloys, although the dislocation strengthening increases continuously.

关键词： Aluminum alloys Precipitation behavior Pre-deformation Precipitation strengthening Dislocation strengthening