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Journal of Materials Science & Technology 2019年第6期35卷 1099-1107页

作者： x.y. jiao J. Wang C.F. Liu Z.P. Guo G.D. Tong S.L. Ma y. Bi y.F. Zhang S.M. xiong School of Materials Science and Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Automobile Safety and Energy Tsinghua University Beijing China China FAW Foundry Co. Ltd. Changchun 130011. China

The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron x-ray tomography with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. Microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcracks originated around pores and PSPs tended to converge on the main cracks to decrease the energy required for crack propagation.

关键词： Hypereutectic Al-Si alloy Primary silicon particles Porosity Fracture morphology High pressure die casting

Propagation behavior of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with line defects

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Acta Mechanica Sinica 2014年第5期30卷 703-713页

作者： y.Pang F.-y.jiao J.-x.Liu Department of Engineering Mechanics Shijiazhuang Tie Dao University School of Mathematics and Physics University of Science and Technology Beijing

Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.

关键词： 1D phononic crystal Piezoelectric/piezomag- netic. Elastic wave Line defect Stiffness matrix method

The microstructure characteristics and fracture behavior of the polyhedral primary iron-rich phase and plate-shaped eutectic iron-rich phase in a high-pressure die-cast AlSi10MnMg alloy

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Journal of Materials Science & Technology 2023年第9期140卷 201-209页

作者： x.y.jiao y.x.Liu J.Wang W.N.Liu A.x.Wan Stuart Wiesner S.M.xiong School of Materials Science and Engineering Northeastern UniversityShenyang 110819China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory of Lightweight Structural Materials Liaoning ProvinceNortheastern UniversityShenyang 110819China Key Laboratory for Advanced Materials Processing Technology Tsinghua UniversityBeijing 100084China Shanghai Synchrotron Radiation Facility Shanghai Advanced Research InstituteChinese Academy of SciencesShanghai 201204China Ein Unternehmen der ALUMINIUM RHEINFELDEN Group RHEINFELDEN 79618Germany

The characterization of multiple iron-rich phases in high-pressure die-cast AlSi10MnMg alloy was *** was focused on the formation and fracture behavior of the primary iron-rich phase((P-IMC)_(I))formed in the shot sleeve and plate-shaped eutectic iron-rich phase in high-pressure die cast(HPDC)AlSi10MnMg *** show that multiple types of iron-rich phases with various morphologies,in-cluding primary iron-rich phases(polyhedral(P-IMC)_(I) and(P-IMC)_(II))and eutectic iron-rich phases(plate-shaped,net shape,and fish-bone shape),were found in HPDC ***(P-IMC)_(I) formed in the shot sleeve were distributed in the interface between primaryα-Al and binary Al-Si *** size(P-IMC)_(II) and various eutectic iron-rich phases formed in the die cavity and they were distributed in Al-Si binary *** primary iron-rich phases belonged to a simple cubic crystal structure with a lattice constant a=1.265 nm and they exhibited a lateral growth characteristic with a termination of{110}surface.βphase was surrounded byδphase and they coexisted in a plate-shaped iron-rich ***-density stacking fault inβphase andδ/βinterface provided an excellent nucleation site forδ*** mechanical behavior,the stress concentration caused by eutectic iron-rich phases was far less than(P-IMC)_(I) and it would not cause crack initiation along the eutectic cluster *** addition,(P-IMC)_(I) showed the worst deformation coordination with primaryα-Al while the plate-shaped eutectic iron-rich phase exhibited similar deformation characteristics with silicon particles.

关键词： AlSi10MnMg High-pressure die casting Multiple iron-rich phases

Analysis on the velocity relationship and deceleration of long-rod penetration

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Acta Mechanica Sinica 2019年第4期35卷 852-865页

作者： W.J.jiao x.W. Chen Department of Modern Mechanics University of Science and Technology of China Hefei230027 China Institute of Systems Engineering China Academy of Engineering Physics Mianyang621999 China The State Key Lab of Explosion Science and Technology Beijing Institute of Technology Beijing100081 China Advanced Research Institute of Multidisciplinary Science Beijing Institute of Technology Beijing 100081 China

The relationship between the average penetration velocity,UˉUˉ,and the initial impact velocity, V0V0,in long-rod penetration has been studied recently. Experimental and simulation results all show the linear relationship between UˉUˉ and V0V0 over a wide range of V0V0 for different combinations of rod and target materials. However, the physical essence has not been fully *** this paper, the Uˉ?V0Uˉ?V0relationship is profoundly analyzed using hydrodynamic model and Alekseevskii-Tate model. Especially, the explicitUˉ?V0Uˉ?V0 relationships are derived fromapproximate solutions of Alekseevskii-Tate model. Besides, the decelerationin long-rod penetration is discussed. The decelerationdegree is quantified by adeceleration index,α=2μˉ/(KΦJp)≈ypρ?1/2p(ρ?1/2p+ρ?1/2t)V?20α=2μˉ/(KΦJp)≈ypρp?1/2(ρp?1/2+ρt?1/2)V0?2, which is mostly related to the impact velocity, rod strength and rod/target densities. Thus, the state of penetration process can be identified and designed in experiments.

关键词： Long-rod penetration Average penetration velocity Initial impact velocity Alekseevskii-Tate model Deceleration

Thermal stability and deformation mechanisms in Ni-Co-Fe-Cr-Al-Ti-Nb-type nanoparticle-strengthened high-entropy alloys

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Journal of Materials Science & Technology 2023年第36期167卷 171-183页

作者： J.x.Hou J.y.Zhang J.x.Zhang J.H.Luan y.x.Wang B.x.Cao y.L.Zhao Z.B.jiao x.J.Liu W.W.Song P.K.Liaw T.yang Department of Materials Science and Engineering Hong Kong Institute for Advanced StudyCity University of Hong KongHong KongChina School of Materials Science and Engineering Harbin Institute of Technology(Shenzhen)Shenzhen 518055China Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHong KongChina Steel Institute RWTH Aachen UniversityAachen 52072Germany Institute of Materials Engineering University of KasselKassel 334125Germany Department of Materials Science and Engineering The University of TennesseeKnoxvilleTN 37996-2200USA City University of Hong Kong China

The precipitate morphologies,coarsening kinetics,elemental partitioning behaviors,grain structures,and tensile properties were explored in detail for L1_(2)-strengthened Ni_(39.9)Co_(20)Fe_(15)Cr_(15)Al_(6)Ti_(4-x)Nb_(x)B_(0.1)(x=0 at.%,2 at.%,and 4 at.%)high-entropy alloys(HEAs).By substituting Ti with Nb,the spheroidal-to-cuboidal precipitate morphological transition,increase in the coarsening kinetics,and phase decomposition upon aging at 800°C *** excessive addition of Nb brings about the grain boundary precipitation of an Nb-rich phase along with the phase decomposition from the L1_(2)to lamellar-structured D019 phase upon the long-term aging *** partially substituting Ti with Nb,the chemically complex and thermally stable L12 phase with a composition of(Ni_(58.8)Co_(9.8)Fe_(2.7))(Al_(12.7)Ti_(5.8)Nb_(7.5)Cr_(2.3))ensures the stable phase structure and clean grain boundaries,which guarantees the superb high-temperature mechanical properties(791±7 MPa for yielding and 1013±11 MPa for failure)at 700℃.Stacking faults(SFs)were observed to prevail during the plastic deformation,offering a high work-hardening capability at 700°*** anomalous rise in the yield strength at 800℃was found,which could be ascribed to the multi-layered super-partial dislocations with a cross-slip configuration within the L1_(2)particles.

关键词： High-entropy alloys Coarsening kinetics Coherent precipitation strengthening Mechanical properties

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

Heavy fermions in high magnetic fields

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Chinese Physics B 2019年第1期28卷 25-38页

作者： M Smidman B Shen C y Guo L jiao x Lu H Q yuan Center for Correlated Matter and Department of Physics Zhejiang UniversityHangzhou 310058China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

Heavy fermion materials are prototypical strongly correlated electron systems, where the strong electron–electron interactions lead to a wide range of novel phenomena and emergent phases of matter. Due to the low energy scales, the relative strengths of the Ruderman–Kittel–Kasuya–yosida(RKKy) and Kondo interactions can often be readily tuned by non-thermal control parameters such as pressure, doping, or applied magnetic fields, which can give rise to quantum criticality and unconventional superconductivity. Here we provide a brief overview of research into heavy fermion materials in high magnetic fields, focussing on three main areas. Firstly we review the use of magnetic fields as a tuning parameter,and in particular the ability to realize different varieties of quantum critical behaviors. We then discuss the properties of heavy fermion superconductors in magnetic fields, where experiments in applied fields can reveal the nature of the order parameter, and induce new novel phenomena. Finally we report recent studies of topological Kondo systems, including topological Kondo insulators and Kondo–Weyl semimetals. Here experiments in magnetic fields can be used to probe the topologically non-trivial Fermi surface, as well as related field-induced phenomena such as the chiral anomaly and topological Hall effect.

关键词： heavy fermions high magnetic fields quantum phase transitions heavy fermion superconductivity topological Kondo systems

Changes in fine root biomass of Picea abies forests:predicting the potential impacts of climate change

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Journal of Plant Ecology 2018年第4期11卷 595-603页

作者： Z.y.yuan x.R.Shi F.jiao F.P.Han State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Soil and Water ConservationNorthwest A&F UniversityYanglingShaanxi 712100China Institute of Soil and Water Conservation Chinese Academy of Science and Ministry of Water ResourceYanglingShaanxi 712100China

Aims the impact of global warming on belowground processes,espe-cially on fine root production,is poorly understood in comparison with its aboveground *** Here,we compiled 227 measurements to assess the influence of temperature and precipitation on fine root biomass of Norway spruce(Picea abies[L.]Karst)forest ecosystems in the Eurasia boreal *** Findings We found that fine root biomass decreased significantly with *** was a biomass increase of 0.63 Mg ha−1 and 0.32 Mg ha−1 for fine rootsy,with 1°C increase of mean annual *** was an increase of 0.5 and 0.1 Mg ha−1 per 100 mm year−1 precipitation for the two size classes of fine *** the adaption of root production can match the pace of global warming and water is not a limiting factor for plant growth,fine root biomass would be expected to increase by 40-140%in response to the predicted increase in tem-perature(3-10°C)over the next *** analyses highlighted the strongly positive influences of temperature and precipitation on belowground function,suggesting that predicted future climate change could substantially enhance belowground biomass in the boreal region where the greatest warming is *** potential increase of belowground biomass,coupled with aboveground biomass,may provide a better understanding of climate-ecosystem feedbacks.

关键词： boreal forest carbon climate change fine roots latitudinal gradient mean annual temperature and precipitation Norway spruce Picea abies production and biomass

The characterization of Fe-rich phases in a high-pressure die cast hypoeutectic aluminum-silicon alloy

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Journal of Materials Science & Technology 2020年第16期47卷 54-62页

作者： x.y.jiao C.F.Liu Z.P.Guo G.D.Tong S.L.Ma y.Bi y.F.Zhang S.M.xiong School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory for Advanced Materials Processing Technology Tsinghua UniversityBeijing 100084China China FAW Foundary Co. LTDChangchun 130011China

Both microstructural characteristics and fracture behavior of Fe-rich phases in a high-pressure die-cast hypoeutectic Al-Si alloy were *** was focused on the morphology and formation mechanism of Fe-rich phases,together with their influence on *** show that primary Ferich phases exhibited in blocky shape precipitated from liquid while secondary Fe-rich phase in a large net shape was distributed along eutectic boundary participating in a ternary eutectic *** synchrotron x-ray tomography characterization,three Fe-rich phases with different morphologies,i.e.,polyhedral shape,fine compact shape and Chinese script-type shape were extracted along the radial *** slow-shot speed promoted the polyhedral Fe-rich phase to precipitate in slow-shot sleeve while decreased the formation of fine compact and Chinese script-type Fe-rich phases in die *** of a worse deformation compatibility,polyhedral Fe-rich phases fractured and became stress concentration sources before the failure of the casting.

关键词： Hypoeutectic Al-10Si Fe-rich phases Fracture morphology High pressure die casting

Novel transcatheter aortic heart valves exhibiting excellent hemodynamic performance and low-fouling property

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Journal of Materials Science & Technology 2019年第1期35卷 207-215页

作者： F.Guo K.jiao y.Bai J.Guo Q.Chen R.yang x.Zhang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China School of Textile and Material Engineering Dalian Polytechnic University Lumenous Peiertech

Transcatheter aortic heart valves(TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate(PEGDA) hydrogels and anisotropic highshrinkage polyethylene terephthalate/polyamide6(PET-PA6) fabric(PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses(DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties(i.e., storage moduli ~23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ~9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic(contact angle ~41.6°± 3.8°) and had low-fouling properties without platelet adhesion,suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area(1.75cm2) and low regurgitation(3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore,PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future.

关键词： Transcatheter aortic heart valve Textile fabric Poly(ethylene glycol)diacrylate Anti-fouling