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THE APPARENT VISCOSITy OF SEMI-SOLID AZ91D ALLOy AT STEADy STATE

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Acta Metallurgica Sinica(English Letters) 2002年第6期15卷 505-510页

作者： Z.S. Zhen, W.M. Mao, S.j. Van, A.M. Zhao, C.L. Cui and x.y. ZhongSchool of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083China

The rheological behavior of semi-solid AZ91D at steady state is studied usinga Couette type viscometer in the present paper. The results show that the apparent viscosity ofsemi-solid AZ91D at the steady state increases with the solid fraction increasing, and goes upsharply when the solid fraction reaches a certain value, which is called critical fraction. Inaddition, the apparent viscosity of semi-solid AZ91D at the steady state takes on a distinctdowntrend with the shearing rate increasing, which indicates a strong shear thinning property. Inaddition, the critical solid fraction becomes higher under larger shearing rate, owing to the moreglobular shape of the solid particles. Based on the present experiment results, an empiricalequation is built as that, relating the steady state apparent viscosity of semi-solid AZ91D with thesolid fraction f_s and shearing rate gamma at the same time: eta_(app)=10.74 exp (6.95 f_s)gamma^(-0.86).

关键词： rheological behavior magnesium alloy semi-solid viscosity viscometer

Hard yet tough and self-lubricating(CuNiTiNbCr)C_(x) high-entropy nanocomposite films:Effects of carbon content on structure and properties

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journal of Materials Science & Technology 2024年第6期173卷 20-30页

作者： y.T.Li x.M.Chen x.K.Zeng M.Liu x.jiang y.x.Leng Key Laboratory of Advanced Technologies of Materials Ministry of EducationSchool of Materials Science and EngineeringSouthwest Jiaotong UniversityChengdu 610031China Key Laboratory of Noise and Vibration Research Institute of AcousticsChinese Academy of SciencesBeijing 100190China State Key Laboratory of Acoustics Institute of AcousticsChinese Academy of SciencesBeijing 100190China School of Mechanical and Electrical Engineering Mianyang Teachers’CollegeMianyang 621000China

The single-phase high-entropy alloy film is difficult to meet severe friction conditions due to its low hardness and high friction ***-composite structure film is composed of at least two separated phases,showing the properties of strength and toughness integration and excellent wear *** design of nanocomposite structures can effectively improve the mechanical properties and tribological properties of high-entropy alloy *** this study,the(CuNiTiNbCr)C_(x) nanocomposite high-entropy films(HEFs)integrated with high hardness,high toughness,and self-lubrication were synthesized by the double-target co-sputtering *** effect of carbon content on microstructure,mechanical properties,and tribological properties of(CuNiTiNbCr)C_(x) films was *** the increase of carbon content in the HEFs,the carbon atoms preferentially react with Ti,Nb,and Cr to form a(TiNbCr)C ceramic-reinforced phase,and then the excess carbon atoms precipitate in the form of amorphous carbon(a-C)lubricating phase in the *** structure of the HEFs changes from an amorphous structure to a nanocomposite structure of amorphous(amorphous CuNiTiNbCr phase+a-C phase)/nanocrystalline(TiN-bCr)C *** the carbon content is about 21.2 at.%,the carbide phase in the film reaches saturation and the hardness and modulus of the films are highest,which are 18 GPa and 228 GPa,*** HEFs with a carbon content of 44.0 at.%show the best toughness and tribological properties with a friction coefficient of 0.16 and a wear rate of 2.4×10^(-6) mm^(3)/(N m),which is mainly attributed to the excellent resistance to fatigue crack growth and the interfacial lubricating layer formed in the friction *** nanocomposite(CuNiTiNbCr)C_(x) HEFs show very promising application prospect in the field of friction protection.

关键词： High-entropy films Nanocomposite Double-target co-sputtering Strengthening-toughening Tribological properties

Oxidation Performance and Interdiffusion Behaviour of two MCrAly Coatings on a Fourth-Generation Single-Crystal Superalloy

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Acta Metallurgica Sinica(English Letters) 2022年第4期35卷 679-692页

作者： K.j.Tan j.j.Liang x.G.Wang x.P.Tao j.Gong C.Sun y.Z.Zhou x.F.Sun Institute of Metal Research Chinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China

The oxidation behaviour of a fourth-generation single-crystal superalloy without coating and with two types of MCrAly coatings at 1140℃was *** results showed that both coatings greatly improved the oxidation resistance of the superalloy,and the addition of Hf further improved the oxidation resistance by pinning the oxide layer into the *** and after oxidation,obvious Cr and Al interdiffusion was *** Cr diffusion induces the precipitation of a topologically close-packed phase,while the diffusion of Al affects the structure of theγ/γ’phase,the solubility of refractory elements,and the formation of an interdiffusion zone.

关键词： Superalloys Metal coatings Oxidation Electron probe microanalyser(EPMA) Element diffusion

EFFECT OF SILICON ON PRODUCING DUCTILE IRON WITH COMPLEx STRUCTURE OF BAINITE AND MARTENSITE

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Acta Metallurgica Sinica(English Letters) 1998年第1期11卷 25-28页

作者： y.P.Zhang j.x.Zhu y.Q.Wang j.y.Su xi'an Univ of Technology Xi'an China

This paper deals with an important role of silicon in producing ductile iron with quenched complex structure of bainite and martensite. The samples are cast in permanent mold and quenched in solution of sodium silicate. The result of thc experiments shows that the austenizing temperature should rise with increasing silicon content, otherwise much undissolved ferrite is present in the matrix after quenching. However the undissolvec ferrite can be decreased greatly or even eliminated by adding appropriate amount of ooron. On this condition, the amount of bainite gets increasing and the amount of residual austenite decreasing with the silicon cortent increasing. An approach has also been made to the mechanism of the effect of silicon on the transformation of bainite in ductile iron. The T.T.T. curves measured show that the increase of sllicon content causes the curve to shift to the left. This is quite different from the fact in steel.

关键词： ductile iron,silicon content bainite martensite

Rare-earth-niobate high-entropy ceramic foams with enhanced thermal insulation performance

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journal of Materials Science & Technology 2022年第21期116卷 94-102页

作者： R.W.yang y.P.Liang j.xu x.y.Meng j.T.Zhu S.y.Cao M.y.Wei R.x.Zhang j.L.yang F.Gao State Key Laboratory of Solidification Processing MIIT Key Laboratory of Radiation Detection Materials and DevicesSchool of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an710072China NPU-QMUL joint Research Institute of Advanced Materials and Structure Northwestern Polytechnical UniversityXi’an710072China State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing100084China State Key Laboratory of Materials Processing and Die&Mould Technology School of Materials Science and EngineeringHuazhong University of Science and TechnologyWuhan430074China

The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation *** this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)y_(0.2)Er_(0.2)yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming ***-scale analysis reveals that high entropy causes atom displacement and lattice *** high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room ***-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal *** is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance *** research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.

关键词： Rare-earth niobate High-entropy ceramic foams Particle-stabilized foaming Atomic-scale analysis Thermal conductivity

SURFACE ANALySIS OF ALUMINUM ALLOyS INFLUENCED By SULFATE- REDUCING BACTERIA

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Acta Metallurgica Sinica(English Letters) 1999年第5期12卷 867-873页

作者： x. L. Wu, j.H. Liu and x.y. Chen Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China

The morphology and chemical compositions of surface and corrosion phases for two aluminum alloys(7075 and 2024 ) in the aqueous mediums containing sulfate reducing bacteria(SRB) were studied by the methods of scanning electron microscopy (SEM) and energy dispersive x ray analysis (EDxA). The results showed that serious pitting corrosion took place when aluminum alloys were exposed in the mediums containing SRB, whereas no pitting corrosion were found on the surfaces of aluminum alloys only exposed in blank mediums non containing SRB. It was demonstrated with EDxA that corrosion of aluminum alloys exposed in the solutions containing SRB, whereas the corrosion in the solution non containing microorganisms was attributed to the presence of chloride ions(Cl ).

关键词： aluminum alloys sulfate reducing bacteria pitting surface analysis

Relationship of Corrosion Behavior Between Single-Phase Equiatomic CoCrNi,CoCrNiFe,CoCrNiFeMn Alloys and Their Constituents in NaCl Solution

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Acta Metallurgica Sinica(English Letters) 2021年第11期34卷 1574-1584页

作者： D.P.Wang j.W.Shen Z.Chen F.G.Chen P.y.Guo y.x.Geng y.x.Wang School of Materials Science and Engineering Jiangsu University of Science and TechnologyZhenjiang 212003China

The composition is a significant issue for corrosion resistance of metallic *** reveal the correlation of corrosion behavior between multiprinciple alloys and their constituents,a series of single-phase equiatomic alloys of CoCrNi,CoCrNiFe and CoCrNiFeMn was *** electrochemical and scanning electron microscope results demonstrated that corrosion resistance of the equiatomic alloys in 0.1 M NaCl solution is located in the range but not the average value of their constituents.x-ray photoelectron spectroscopy analysis indicated that the protective performance of passive film is mainly determined by the constituent with the highest corrosion resistance and the breakdown of passive film is mainly dominated by the elements with the highest corrosion *** findings can guide the materials design of multiprinciple alloys with expected corrosion performance.

关键词： High-entropy alloy Corrosion Constituent x-ray photoelectron spectroscopy(xPS) Passive films

Influence of the velocity barrier on the massive Dirac electron transport in a monolayer MoS2 quantum structure

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Frontiers of physics 2020年第3期15卷 113-121页

作者： x.-j.Hao R.-y.yuan j.-j.jin y.Guo Center for Theoretical Physics Department of PhysicsCapital Normal UniversityBeijing100048China Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics Tsinghua UniversityBeijing100084China Collaborative Innovation Center of Quantum Matter BeijingChina

Using the transfer matrix method,spin-and valley-dependent electron transport properties modulated by the velocity barrier were studied in the normal/ferromagnetic/normal monolayer MoS2 quantum *** on Snell’s Law in optics,we define the velocity barrier asξ=v2/v1 by changing the Fermi velocity of the intermediate ferromagnetic region to obtain a deflection condition during the electron transport process in the *** results show that both the magnitude and the direction of spin-and valley-dependent electron polarization can be regulated by the velocity barrier.−100%polarization of spin-and valley-dependent electron can be achieved forξ>1,while 100%polarization can be obtained forξy transport always occur at a large incident *** addition,the spin-and valley-dependent electron transport considerably depends on the length kFL and the gate voltage U(x)of the intermediate ferromagnetic *** findings provide an effective method for designing novel spin and valley electronic devices.

关键词： velocity barrier monolayer MoS2 spin valley polarization

STRUCTURE AND PROPERTIES OF Cu-Co MULTILAyER FILMS PRODUCED By ELECTRODEPOSITION

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Acta Metallurgica Sinica(English Letters) 1997年第2期10卷 115-119页

作者： xue, j.y. Wu, j.x. yang, D.j. Univ of Science and Technology Beijing Beijing China

Multilayer Cu-Co film has been produced from a single bath by the method of pulse electrodeposition. Its structure and some magnetic properties were analysed by TEM,AES, xRD and VSM. The results indicated that the film was layed structure, consisted of alternating pure copper and copper-cobalt alloy layers. The results have shown the possibility of producing multilayer films with perpendicular magnetic anisotropy byelectrodeposition.

关键词： electrodeposition copper-cobalt multilayer