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Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy

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Journal of Materials Science & Technology 2018年第10期34卷 1739-1746页

作者： Q. Chu w.y. Li X.w. yang J.J. Shen A. Vairis w.y. Feng w.B. wang State Key Laboratory of Solidification Processing Shaanxi Key Laboratory of Friction Welding Technologies Northwestern Polytechnical University Xi'an710072 China Helmholtz-Zentrum Geesthacht Institute of Materials Research Materials Mechanics Geesthacht 21502 Germany Mechanical Engineering Department TEl of Crete Heraklion Crete 71004 Greece China PSw Center Beijing 100024 China

In this work, a third generation AI-Li alloy has been successfully spot welded with probeless friction stir spot welding （P-FSSw）, which is a variant of conventional friction stir welding. The Box-Behnken exper-imental design in response surface methodology （RSM） was applied to optimize the P-FSSw parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/rain. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction （EBSD） and differential scanning calorimetry （DSC） were used for microstructure evolution and property analysis. The precipitation of GP zone and AI3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.

关键词： Probeless friction stir spot welding Precipitation Mechanical property Fracture mechanism

Synthesis and properties of poly(1-phenyl-1-octyne)s containing stereogenic and chromophoric pendant groups

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Science China Chemistry 2009年第10期52卷 1691-1702页

作者： LAM Jacky w.y. JIM Cathy K.w. KwOK Hoi Sing Department of Chemistry The Hong Kong University of Science & Technology Center for Display Research The Hong Kong University of Science & Technology

Poly(1-phenyl-1-octyne)s containing different stereogenic and chromophoric pendants {-[(C6H13)C= C(C6H4-p-CO2-R)] n -R = [(1S)-endo]-(?)-borneyl (P3), (1R,2S,5R)-(?)-menthyl (P4), -C6H4-p-(1R,2S,5R)-(?)-menthyl (P5), 2-napthyl (P6), 4-biphenylyl (P7)} have been designed and synthesized. The polymers are prepared in moderate yields by wCl6-Ph4Sn and possess high molecular weights (M w up to 64000). The structures and properties of the polymers are characterized and evaluated by NMR, TGA, UV, CD, PL, and EL analyses. All the polymers are thermally stable and their temperatures for 5% weight loss locate in the range of 300 to 416°C under nitrogen. The energy band gaps of all the polymers are ～3.0 eV. Polymers P4 and P5 show CD absorptions associated with the helicity of the polymer segments. Excitation of the THF solutions of P3–P7 by UV irradiation gives strong blue lights of ～485 nm with quantum yields higher than 20%. The thin films of the polymers also emit in the same spectral region, indicative of little aggregation-caused quenching of light emission. Multilayer EL devices with a configuration of ITO/Polymer:PVK/BCP/Alq3/LiF/Al are constructed, which emit blue lights of ～487 nm. The maximum luminance and external quantum efficiency vary with the pendant groups, with P6 exhibiting the highest external quantum efficiency of 0.16%. The spectra stability of the EL devices is outstanding and the EL peak maximum experiences little change with the applied voltage.

关键词： chiral photoluminescence polyacetylene electroluminescence helicity

The Control of Search and Rescue Robots with the General Suppression Control Framework

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Restriction of Intramolecular Motion(RIM):Investigating AIE Mechanism from Experimental and Theoretical Studies

第二十六届中国控制会议

作者： Lau Henry y.K. Ko Albert w.y. Department of Industrial and Manufacturing Systems Engineering The University of Hong KongThe Pokfulam of Hong KongP.R.China

ISBN: (纸本)7900719229;9787900719225

The paper described the use of the general suppression control framework（GSCF）for the control and coordination of a team of search and rescue robots undertaking exploration *** study adopts the biological analogy of the hu-man immune system to derive the GSCF having the behavior of immunological *** framework directs the coordination of these robots in tackling search and rescue operations in an unstructured *** study is performed to demonstrate the effectiveness of the control framework.

关键词： distributed control modular robots artificial immune system

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Chemical Research in Chinese Universities 2021年第1期37卷 1-15页

作者： ZHANG Jianyu ZHANG Haoke LAM Jacky w.y. TANG Ben Zhong Department of Chemistry Hong Kong Branch of Chinese National Engineering Research Centre for Tissue Restoration and ReconstructionInstitute for Advanced Studyand Department of Chemical and Biological EngineeringThe Hong Kong University of Science&TechnologyClear Water BayKowloonHong KongP.R.China MOE Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science and EngineeringZhejiang UniversityHangzhou310027P.R.China Center for Aggregation-Induced Emission SCUT-HKUST Joint Research InstituteState Key Laboratory of Luminescent Materials and DevicesSouth China University of TechnologyGuangzhou510640P.R.China Guangzhou Development District AIE InstituteGuangzhou510530P.R.China

Mechanistic studies promote scientific development from phenomena to ***-induced emission(AIE),as an unusual photophysical phenomenon,builds the bridge between molecular science and aggregate *** the twenty-year development of AIE,restriction of intramolecular motion(RIM)has been verified as the working mechanism of AIE *** this review,these mechanistic works about RIM are summarized from experimental and theoretical ***,the experimental studies are introduced from three parts:external rigidification,structural modification and structural *** the theoretical part,calculations on the low-frequency motion of AIEgens have been performed to prove the RIM *** virtue of the theoretical calculations,some new mechanisms are proposed to supplement the RIM,such as restriction of access to conical intersection,suppression of Kasha transition,restriction of access to dark state,*** is foreseeable that the RIM mechanism will unify the photophysical theories for both molecules and aggregates,and inspire more progress in aggregate science.

关键词： Aggregation-induced emission(AIE) Restriction of intramolecular motion Photophysical mechanism Aggregate science

Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

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Journal of Materials Science & Technology 2011年第11期27卷 1025-1028页

作者： D. Li F.y. Meng X.Q. Ma L.J. Qiao w.y. Chu Department of Physics University of Science and Technology Beijing Beijing 100083 China Corrosion and Protection Center Key Lab of Environmental Fracture （Ministry of Education） University of Science and Technology Beijing Beijing 100083 China

The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.9. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking （SCC）. Molecular dynamics （MD） simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.

关键词： Molecular dynamics simulation Dislocation emission Crack propagation Porouslayer Stress intensity

INFLUENCE OF THE NONMAGNETIC METAL SPACER ON THE MAGNETIC PROPERTIES AND MICROSTRUCTURE OF THE MULTILAyER FILMS

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Acta Metallurgica Sinica(English Letters) 2006年第4期19卷 235-243页

作者： M.H. Li G.H. yu F.w. Zhu H.w. Jiang w.y. Lai College of Mechanical Engineering South China University of Technology Guangzhou 510640 China Department of Materials Physics University of Science and Technology Beijing Beijing 100083 China Department of Physics Capital Normal University Beijing 100037 China Institute of Physics Chinese Academy of Sciences Beijing 100080 China

Ta / NiFe/Bi （ Ag, Cu ）/FeMn/Ta and Ta / NiFe1/FeMn / Bi （ Ag, Cu ）/NiFen/Ta films were prepared by magnetic sputtering. The texture and the dependences of the exchange-coupling field on the thickness of Bi, Ag, and Cu in Ta/NiFe/Bi（Ag, Cu） /FeMn/Ta and Ta/NiFe/FeMn/Bi（Ag, Cu）/NiFe/Ta films were studied. XPS results indicate that the Bi atoms migrated into the FeMn layer during the deposition process and a FeMnBi alloy was probably formed or the Bi atoms existed as an impurity in the FeMn layer in Ta/NiFe/Bi（Ag, Cu ）/FeMn/Ta. Otherwise, in Ta/NiFe/FeMn/Bi （Ag, Cu）/NiFe/Ta films, Bi, Ag, and Cu atoms do not remain entirely at the interface of the FeMn/ NiFeⅡfilm, but at least partly segregate to the surface of the NiFe film.

关键词： NiFe/FeMn nonmagnetic spacer exchange coupling XPS (X-ray photoelectron spectroscopy)

Monotropic smectic A to double layer smectic C transition of biphenyl containing liquid crystal acetylene

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Chinese Chemical Letters 2011年第11期22卷 1355-1358页

作者： Zhen Qiang yu CaiZhenZhu Zhe Zhang Jian Hong Liu Jacky w.y. Lam Ben Zhong Tang Shenzhen Key Laboratory of Functional Polymers and School of Chemistry and Chemical Engineering Shenzhen University Shenzhen 518060 China Department of Chemistry The Hong Kong University of Science and Technology Clear Water BayKowloonChina

5-[（4＇-Heptoxy-4-biphenylyl）carbonyloxy]-1-pentyne（A-3,7） was synthesized and the phase structures and transitions were investigated by differential scanning calorimetry（DSC）,wide angle X-ray diffraction（wAXD）,polarized light microscopy（PLM） and the molecular packing in the crystal and liquid crystalline phases were simulated by molecular dynamic *** results showed that the sample formed thermodynamically metastable SmA and SmC_2 phases before crystallized during cooling and the crystal phase directly transformed into isotropic phase during heating.

关键词： Liquid crystal Phase structure Phase transition Smectic phase X-ray diffraction

EFFECT OF VACUUM HEAT TREATMENT ON OXIDATION BEHAVIOR OF SPUTTERED NiCrAly COATING

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Acta Metallurgica Sinica(English Letters) 2002年第1期15卷 61-66页

作者： M.H. Li X.F. Sun Z.y. Zhang H.R. Guan w.y. Hu Z.Q Inst. of Metal Res. Chinese Acad. of Sci. Shenyang 110016 China

A bond coat for thermal barrier coating (TBC), NiCrAly coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputtered NiCrAly coating has been investigated. The as-sputtered NiCrAly coating consists of γ-Ni and b-NiAl phases. After vacuum heat treatment, the sputtered NiCrAly coating mainly consists of γ'-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isothermal oxidation of sputtered NiCrAly coating with and without vacuum heat treatment has been performed at 1000℃. It is shown that a-Al2O3 formed during vacuum heat treatment acts as nuclei for the formation of a-Al2O3, and the protective a-Al2O3 scale is formed more rapidly on the vacuum heat treated NiCrAly coating than that formed on the untreated coating. Also the a-Al2O3 scale has a better adherence to the vacuum heat treated NiCrAly coating. Therefore the vacuum heat treatment improves the oxidation resistance of sputtered NiCrAly coating.

关键词： vacuum heat treatment oxidation sputtered NiCrAly coating

Functional Electrical Stimulation Improves Motor Recovery of the Lower Extremity and walking Ability of Subjects with First Acute Stroke A Randomized Placebo-Controlled Trial

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Functional Electrical Stimulation Improves Motor Recovery of...