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STUDy oN THE MEcHANISM oF gRAPHITIZATIoN IN MoLTEN cAST IRoN PRoMoTED By ELEcTRoPULSE DIScHARgE

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Acta Metallurgica Sinica(English Letters) 2004年第6期17卷 790-794页

作者： g.W.chang J.S.Wang J.Z.Wang q.g.Xue o.q.Zhou D.q.cang Dept.Materials＆chemicalEng. LiaoningInstituteofTechnologyJinzhou121001China SchoolofMetallurgy BeijingUniversityofScience＆Technology.Beijing100083China

From the points of both molten cast iron structure and the appearing ratio of electrons in outer-layer of different atoms, analysis on enhancement mechanism of graphitization ability after processing of the iron by pulse electric discharge has been made, and the theory has been proofed by corresponding experiments. The results show that when the molten cast iron is being processed by pulse electric discharge, both the size of crystal embryos that composed by Fe and c atoms as well as the number of clusters can be reduced, even be separated by such discharging; consequently results in the segre- gation of c atoms in the molten cast iron near the cathode of discharging. The nucleation of graphite in these areas of the iron has been promoted at the discharging temperature; even though such degree has not been reached, the most favorable nucleation conditions of graphite can be at least created. Under the preconditions of not breaking up the graphite crystal embryos, with proper adjustment of discharging frequency, the stronger of the electric field and the longer of the pulsation treatment time are, the more graphitization ability of the molten cast iron is. The theoretical analysis on the above rules consists well with experimental results.

关键词： pulsed electric field molten iron-solution graphitization

AN INVESTIgATIoN oF HIgH-TEMPERATURE DEFoRMATIoN STRENgTHENINg AND ToUgHENINg MEcHANISM oF TITANIUM ALLoy

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Acta Metallurgica Sinica(English Letters) 1998年第5期11卷 376-382页

作者： y.g.Zhou W.D.Zing H.q.yu Northwestern Polytechnical Univ Xi'an China

The high-temperature deformation strengthening and toughening mechanisms of titanium alloys have been investigated in this paper. The materials processed by this method produce a new tri-modal microstrvcture, which consists of 10-20% equiaxed alpha, streaky alpha and transformed beta matrix. It is found that the higher ductility of tri-modal microstructure is attributed to the equiaxed alpha's coopemtive slip and coordinated deformation with the transformed beta matrix. The streaky alpha phases not only increase the strength and creep properties, but also increase the fracture toughness. Propagating along grain boundaries between two neighboring streaky alpha phases, cracks in tri-modal microstructure make a more tortuous way, and then the materials show a higher fracture toughness. This new method is applicable to α, near α,α+β and near β titanium alloys.

关键词： titanium alloy high-temperature deformation strengthening and toughening mechanism

THE INTERFAcE oF TERNARy-BoRIDE-BASED HARD cLADDINg MATERIAL

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Acta Metallurgica Sinica(English Letters) 2004年第1期17卷 47-50页

作者： y.g.Wang Z.q.Li D.Zhang State Key Laboratory of Metal Matrix composites Shanghai Jiaotong UniversityShanghai 200030 ChinaMechanical Engineering DepartmentShandong University Jinan 250061 ChinaState Key Laboratory of Metal Matrix CompositesShanghai Jiaotong UniversityShanghai 200030China

The interfacial microstructure of ternary-boride-based hard cladding material (yF-2) has been studied using scanning electron microanalyser (SEM), X-ray diffraction (XRD) and energy disperse spectroscopy (EDS). Results show that there are chemical reactions and elements diffusion in the interfacial zone, which make the interface bonding well and bonding strength ideal at the interface. The results gotten by studying of crack produced by Vickers indentation technique in the interfacial zone show that it is difficult to produce crack in the interface, the crack length in the cladding layer is longer than that to the interface, the crack which propagate to the interface stops at the interface rather than propagates along the interface. This suggests negligible residual stresses have developed because of thermal expansion mismatch. The bonding strength of the interface is 550MPa, which has been gotten by cutting test. The result gotten by analyzing the fracture surface shows that the fracture occurs at the side of cladding layer, which confirms that the bonding strength at the interface is higher than that in the cladding layer.

关键词： ternary boride cladding material interface micro structure

Role of extrusion rate on the microstructure and tensile properties evolution of ultrahigh-strength low-alloy Mg-1.0Al-1.0ca-0.4Mn(wt.%)alloy

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Journal of Magnesium and Alloys 2023年第2期11卷 553-561页

作者： X.q.Liu X.g.qiao R.S.Pei y.q.chi L.yuan M.y.Zheng School of Material Science and Engineering Harbin Institute of TechnologyHarbin 150001China Institut fur Metallkunde und Meterialphysik RWTH Aachen UniversityAachen D-52056Germany

Mg-1.0Al-1.0ca-0.4Mn(AXM1104, wt.%) low alloy was extruded at 200 ℃ with an extrusion ratio of 25 and different ram speeds from 1.0 to 7.0 mm/s. The influence of extrusion rate on microstructure and mechanical properties of the AXM1104 alloy was systematically studied. With the increasing of extrusion rate, the mean dynamically recrystallized(DRXed) grain size of the low alloy and average particles diameter of precipitate second phases were increased, while the degree of grain boundary segregation and the intensity of the basal fiber texture were decreased. With the rising of extrusion rate from 1.0 to 7.0 mm/s, the tensile yield strength(TyS) of the as-extruded AXM1104 alloy was decreased from 445 MPa to 249 MPa, while the elongation to failure(EL) was increased from 5.0% to 17.6%. The TyS, ultimate tensile strength(UTS) and EL of the AXM1104 alloy extruded at the ram speed of 1.5 mm/s was 412 MPa, 419 MPa and 12.0%, respectively,exhibiting comprehensive tensile mechanical properties with ultra-high strength and excellent plasticity. The ultra-high TyS of 412 MPa was mainly due to the strengthening from ultra-fine DRXed grains with segregation of solute atoms at grain boundaries. The strain hardening rate is increase slightly with increasing extrusion speed, which may be ascribed to the increasing mean DRXed grain size with rising extrusion speed. The higher strain hardening rate contributes to the higher EL of these AXM1104 samples extruded at higher ram speed.

关键词： Mg-Al-ca-Mn alloy Ultrafine grain Extrusion rate grain boundary segregation Microstructure Ultrahigh strength

Experimental and numerical study of the effect of pulsatile flow on wall displacement oscillation in a flexible lateral aneurysm model

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Acta Mechanica Sinica 2019年第5期35卷 1120-1129页

作者： L.Z.Mu X.y.Li q.Z.chi S.q.yang P.D.Zhang c.J.Ji y.He g.gao School of Energy and Power Engineering Dalian University of TechnologyDalian 116024China School of Biomedical Engineering Capital Medical UniversityBeijing 100069China The First Affiliated Hospital of University of Science and Technology of china Hefei 230036China

This study experimentally and numerically investigated the effect of pulsatile flow of different frequencies and outflow resistance on wall deformation in a lateral aneurysm.A method for constructing a flexible aneurysm model was developed,and a self-designed piston pump was used to provide the pulsatile flow conditions.A fluid-structure interaction simulation was applied for comparison with and analysis of experimental *** maximum wall displacement oscillation increased as the pulsation frequency and outflow resistance increased,especially at the aneurysm *** is an obvious circular motion of the vortex center accompanying the periodic inflow fluctuation,and the pressure at the aneurysm dome at peak flow increased as the pulsatile flow frequency and terminal flow resistance *** results could explain why abnormal blood flow with high frequency and high outflow resistance is one of the risk factors for aneurysm rupture.

关键词： Lateral aneurysm In vitro experiment Pulsatile flow Wall displacement oscillation Fluid-structure interaction simulation

EXPERIMENTAL STUDy oN BED RESISTANcE cHARAcTERISTIcS oF NoNUNIFoRM SEDIMENT

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Journal of Hydrodynamics 2000年第4期12卷 66-74页

作者： Zhou, g.D. Liu, q.y. Wang, g.X. Hui, y.J. Pang, D.M. Tsinghua Univ. Beijing 100084 China

Under natural circumstances, the bed of fluvial river is composed of nonuniform sediment, and its nonuniform property influences very much the bed resistance and flow characteristics. By using a one-dimensional laser velocimeter, flume experiments are carried out to analyze the resistance characteristics of open channel flow with the bed sediment composed of different representative particles and having different nonuniform properties. By means of separating factors, the factors affecting the bed resistance, including particle diameter, nonuniform property and flow conditions, are studied. A great number of laboratory test results and field data from other investigators have been analyzed.

关键词： Sediments

RESEARcH AND DEVELoPMENT oF HIgH TEMPERATURESTRUcTURAL MATERIALS FoR AERo-ENgINE APPLIcATIoNS

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Acta Metallurgica Sinica(English Letters) 2005年第4期18卷 443-452页

作者： g. q. Zhang Beijing Institute of Aeronautical Materials （BIAM） Beijing 100095 China

The status of research, development of superalloys and materials processing ＆ fabrication technologies for aero-engine applications in china Aviation Industry, with an emphasis on recent achievements at BIAM including directionally solidified and single crystal superalloys for blade and vane applications, wrought superqlloys for aero-engine disks and rings, and powder metalurgy （PM） superalloys for high performance disk applications were described. It was also reviewed the development of new class of high temperature structural materials, such as structural intermetallics, and advanced material processing technologies including rapid solidification, spray forming and so on. The trends of research and development of the above mentioned superalloys and processing technologies are outlined. cast, wrought and PM superalloys are the workhorse materials for the hot section of current aero-engines. New high temperature materials and advanced processing technologies have been and will be the subject of study. It is speculated that high performance, high purity and low cost superalloys and technologies will play key roles in aero-engines.

关键词： superalloy intermetallic materials processing aero-engine application

cREEP BEHAVIoR oF γ-TiAl PoLySyNTHETIcALLy TWINNED cRySTALS

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Acta Metallurgica Sinica(English Letters) 1996年第6期9卷 577-583页

作者： y.g. Zhang J.g. Lin y.J. Zhou and c.q. chen(Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics,Beijing 100083, china Beijing Univ of Aeronautics and Astronautics Beijing China

creep behavior of γ-TiAl polysynthetically twinned (PST) crystals has been investigated at temperature between 700 and 800℃. The results show that the creep behavior of the crystals is strongly dependent on the angle between the lamellar boundaries and loading axis. The samples with the angle φ=45 deg. have the lowest creep resistance, while the samples with φ=0 deg., rather than φ=90 deg.,show the strongest creep resistance. The stress exponent and creep activation energy for the power law creep vary with the orientations of samples, which indicates that the creep mechanisms of the samples with different angle φ are quite *** deformation substructure has been examined by transmission electron microscopy (TEM),which shows that both gliding, perhaps also climbing, of dislocations and twinning contribute to the creep deformation with some particular observation in the samples with φ=90 deg. in which rotation of the γ plates across a true twin boundary was observed, which indicates the deformation mechanism of the samples is different from the samples in other orientations.

关键词： TiAl alloy PST crystal creep behavior lamellar microstructure

LoW cycLE FATIgUE AND DEFoRMATIoN BEHAVIoR IN AN 8090 Al-Li ALLoy

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Acta Metallurgica Sinica(English Letters) 1998年第1期11卷 1-11页

作者： S.H.Ai y.q.Wu Z.g.Wang y.Zhang chinese Acad of Sciences Shenyang China

Low cycle fatigue (LcF)tests under different total strain amplitudes have been conducted in order to ascertain the effect of precipitate sizes on LcF behavior of 8090 Al-Li alloy. A constant strain rate of 3×10-3s-1 and symmetrical triangular waveform were employed for all tests. It is found that the cyclic stress response of the alloy varied with the precipitate sizes and strain amplitudes. The materials in all conditions cyclically handen at first and the higher the strain amplitude, the greater the amount of hardening. The low cyclic flow stress is the highest in the peakaged condition. TEM and SEM observations demonstrated that cyclic stress-strain behavior and fracture mode of Al-Li alloy are closely related to an increase in the dislocation density and interaction between the precipitates and dislocations, sizes of δ particles and pricipitate free zone (PFZ) at grain boundaries.

关键词： Al-Li alloy low cycle fatigue aged condition