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Probing the hydration of composite cement pastes containing fly ash and silica fume by proton NMR spin-lattice relaxation

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science china(Technological sciences) 2010年第6期53卷 1471-1476页

作者： SHE AnMing & YAO Wu key laboratory of advanced Civil engineering materials (Tongji university),ministry of education,Shanghai 200092,china 1. key laboratory of advanced Civil engineering materials (Tongji university) Ministry of Education Shanghai 200092 China

Proton NMR spin-lattice relaxation (T1) was used as a prober for observing the hydration process of composite cement pastes blending fly ash and silica fume during the early *** distribution at initial time,evolution curves and signals intensity of T1 were shown in this *** demonstrate that the T1 distribution curves at initial time exhibit two peaks,which are regarded as two different water phases in the *** evolution curves of T1 are in good agreement with the hydration process of composite pastes and could be roughly divided into four stages:initial period,dormant period,acceleration period and steady *** hydration mechanism for each stage was *** hydration of the composite cement pastes was retarded by the addition of fly ash and silica fume when compared to that of pure ***,the hydration degree of the cement in the blends was promoted.

关键词： NMR relaxation cement fly ash silica fume hydration

Analysis of residual stress distribution along interface asperity of thermal barrier coating system on macro curved surface

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Progress in Natural science:materials International 2011年第3期21卷 262-267页

作者： Ming SONG,Yue MA,Sheng-kai GONG key laboratory of Aerospace materials and Performance(ministry of education), School of materials science and engineering,Beihang university,beijing 100191,china key laboratory of Aerospace materials and Performance (ministry of education) School of Materials Science and Engineering Beihang University Beijing 100191 China

Based on the study of the radial residual stress distribution on the macro curved interfaces of thermal barrier coating system(TBCs) for the hollow curved substrate structures,the hollow four-concentric-circle model was *** the concentric-circle model with a fine scaled sinusoidal interface was proposed to describe the stresses distribution on the rough interface of TBCs with macro curved *** influences of the geometric and thermophysical parameters were discussed by the developed *** results showed that the radial stress on the rough interface can be separated into two sections:the overall level stress from macro surface curvature and the local stress from local asperity of the *** overall level stress was determined by the thicknesses and the thermophysical parameters of each *** has been found that the ratio of local stress and overall level stress was influenced by the interface asperity,the ratio of elastic modulus and the ratio of thermal expansion coefficients of the layers beside the rough ***,the convex macro curvature of the substrate can induce tensile stress onto the *** at the sharp corners of the substrate,the small curvature radius can cause high stress which should be taken more care about the occurrence of spalling cracking at interface

关键词： barrier coating system(TBC) residual stress interface asperity thermal grown oxide(TGO) concentric-circle model

Effects of solidification parameters on microstructure and mechanical properties of continuous columnar-grained Cu-Al-Ni alloy

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Progress in Natural science:materials International 2011年第5期21卷 368-374页

作者： Zhen WANG,Xue-feng LIU,Jian-xin XIE key laboratory for advanced materials Processing,ministry of education, university of science and Technology beijing,beijing 100083,china key laboratory for advanced materials Processing Ministry of Education University of Science and Technology Beijing Beijing 100083 China

Effects of melt temperature and casting speed on microstructure and mechanical properties of Cu-14%Al-3.8%Ni(mass fraction) alloy wires fabricated by continuous unidirectional solidification technology were *** was found that the average size of columnar grain in the alloy decreased and grain boundary turned clear and straight with increasing the casting speed at a given melt *** the melt temperature was up to 1 280℃,theβ1phase gradually transformed into lozenged and lanciformγ’1martensite,as well as parallel-sided plateβ’*** alloy with numerous coarsely dendriticγ2phase has poor mechanical properties due to the difficulty of stress-induced martensitic *** the amount of theγ2phase reduced and the coarse dendriteγ2phase evolved into the fine square particles,the elongation of the alloy increased gradually with a decrease in tensile ***,the plasticity of the alloy could also be improved by increasing the amount and size of martensites,particularly the lanciformγ’*** the alloy was almost composed of coarse lanciformγ’1martensite,the tensile strength and elongation of the alloy could be up to 772 MPa and 18.9%,respectively,and the tensile curve consisted of three transformation platforms.

关键词： shape memory alloy continuous unidirectional solidification columnar grain martensitic transformation

Effects of different pack aluminizing fillers on the aluminide coatings of Ti-6Al-4V alloy and their high-temperature oxidation behaviors

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Rare Metals 2007年第S1期26卷 306-312页

作者： ZHOU Wei,ZHAO Yuguang,and MEI Xuelian key laboratory of Automobile materials of ministry of education,department of materials science and engineering,Jilin university,Changchun 130025,china Jilin Univ Dept Mat Sci & Engn Key Lab Automobile Mat Minist Educ Changchun 130025 Peoples R China

The aluminide coating process of Ti-6Al-4V alloys with different fillers(100wt.% Al_2O_3,50wt% Y_2O_3+50wt.% Al_2O_3 and 100wt.% Y_2O_3) for improvement of the oxidation resistance were *** results show that the filler does not only participate in the aluminizing process,but also has much effect on the coating *** XRD analysis reveals that the aluminide coating with filler Al_2O_3 is predominant with TiAl_3 and TiAl phases;while the aluminide coatings with filler Y_2O_3+Al_2O_3 are predominant with Ti_3Al *** oxidation kinetics shows that different fillers affect greatly the oxidation resistance of aluminide coating,and the oxidation resistance of aluminized specimens with pack aluminizing filler Al_2O_3 are about 5-8 times than that of the aluminized specimens with other pack aluminizing fillers.

关键词： Ti-6Al-4V alloy aluminide coating fillers oxidation

Effect of the cooling rate on plastic deformability of a Zr-based bulk metallic glass

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science china(Physics,Mechanics & Astronomy) 2010年第3期53卷 415-418页

作者： ZHANG Jing, PANG ShuJie & ZHANG Tao key laboratory of Aerospace materials and Performance (ministry of education), department of materials science and engineering, beijing university of Aeronautics and Astronautics, beijing 100191, china 1. key laboratory of Aerospace materials and Performance (ministry of education) Department of Materials Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.

关键词： cooling rate shear band serration bulk metallic glass

Advances in Thermionic Cathode of Tungsten and Molybdenum

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Rare Metals 2001年第3期20卷 137-141页

作者： Jinshu Wang,Meiling Zhou, Tieyong Zuo, Juan Liu, Jiuxing Zhang, Zuoren Nie The key laboratory of advanced Functional materials, ministry of education, School of materials Scence and engineering, beijing Polytechnic university, beijing 100022, china beijing Polytech Univ Sch Mat Sci & Engn Minist Educ Key Lab Adv Funct Mat Beijing 100022 Peoples R China

Several kinds of tungsten thermonic cathodes have been introduced. As a promising alternative for thoriated tungsten, rare earth doped molybdenum cathode has been studied. Compared with the traditional thoriated tungsten, La-Mo cathode has higher emission current density at lower temperature, but it has poor emission stability. In order to improve the emission stability, systematical study on the emission mechanism of La-Mo cathode has been carried out. The life of La-Mo cathode has been improved and has achieved 1400 It, which exceeds the minimum life for practical uses (1000 h). As another alternative for thoriated tungsten cathode, Y-Mo cathode has shown better performance. The thermionic emission capability of Y-Mo cathode is between that of La-Mo cathode and Th-W cathode.

关键词： tungsten molybdenum thermonic cathode emission

Magnetism induced by nonmagnetic dopants in zinc-blende SiC: First-principle calculations

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science china(Physics,Mechanics & Astronomy) 2010年第1期53卷 1-10页

作者： LIU ZhaoQing & NI Jun department of Physics and key laboratory of Atomic and Molecular Nanoscience (ministry of education), tsinghua university, beijing 100084, china 1. department of Physics and key laboratory of Atomic and Molecular Nanoscience (ministry of education) Tsinghua University Beijing 100084 China

Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms as dopants. We find that some nonmagnetic substitutional dopants (mainly the Group IA, Group IIA, Group IIIB, and Group VIIB elements) prefer the spin-polarized ground states with local magnetic moments. In general, the condition for obtaining the local magnetic moments and the magnetic ground state requires that the dopants are p-type and have large electronegativity difference from the neighboring host atoms. The magnetic moments can be tuned over a range between 1 μ B and 3 μ B by doping with the nonmagnetic elements. The nearest-neighbor exchange couplings J 0 between the local magnetic moments are quite large and the codoping method is proposed to increase the dopant concentration. These imply that the nonmagnetic doping in SiC may exhibit collective magnetism. Moreover, the Group IIA Mg and Ca atoms substituting the preferred Si atoms favor the ferromagnetic ground states with the half-metallic electronic properties, which suggests that Mg or Ca substitutional doping on the Si sites in SiC could be a potential route to fabricating the diluted magnetic semiconductors.

关键词： nonmagnetic dopant magnetism SiC diluted magnetic semiconductor first-principle calculation

Microstructural characterization of the Al/Cu/steel diffusion bonded joint

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Rare Metals 2009年第5期28卷 478-481页

作者： BAI Bingzhe GAO Yimin FENG Chun laboratory of advanced materials Department of Materials Science and Engineering Tsinghua University Beijing 100084 China State key laboratory for Mechanical Behavior of materials School of Materials Science and Engineering Xi＇an Jiaotong University Xi＇an 710049 China

A vacuum hot-pressed diffusion method was used to prepare an Al/Cu/steel composite with a gradient structure. The Al/Cu interface was investigated layer by layer by means of scanning electron microscopy, energy dispersive X-ray spectrometry, electron probe microanalysis, and Vickers microhardness. The results show that two kinds of intermetallic compounds, Cu9Al4 adjacent to the Cu side and CuAl2 adjacent to the Al side, are formed in the interface of Al/Cu. The conductivity is 0.369 mS/cm in the intermetallic compound with a thickness of 3.5 μm, higher than that of the intermetallic compound with a thickness of 23 μm, in which the conductivity is 0.242 mS/cm.

关键词： metal composites diffusion bonding intermetallic compounds microhardness interface

Effects of Current Frequency on the Microstructure and Wear Resistance of Ceramic Coatings Embedded with SiC Nano-particles Produced by Micro-arc Oxidation on AZ91D Magnesium Alloy

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Journal of materials science & Technology 2010年第10期26卷 865-871页

作者： Yue Yang and Hua Wu key laboratory of advanced Structural materials,ministry of education,Changchun university of Technology,Changchun 130012,china [a] key laboratory of advanced Structural materials ministry of education Changchun university of Technology Changchun 130012 china

To improve the surface wear resistance of the ceramic coating fabricated by micro-arc oxidation （MAO） on AZ91D magnesium alloy,ceramic coatings embedded with SiC nano-particles at different current frequency （500 Hz,700 Hz,and 900 Hz） were produced during the MAO *** morphology and phase composition of the coatings were investigated by scanning electron microscopy （SEM）,field emission scanning electron microscopy （FESEM）,and X-ray diffraction （XRD）.The surface roughness of the coatings was characterized by confocal laser scanning microscopy （CLSM）.Simultaneously,the tribological properties of the composite coatings were evaluated by using a universal materials tester （UMT）.The results shows that the wear resistance of the ceramic coatings with SiC nano-particles was improved significantly compared to the ceramic coatings without SiC ***,the composite coating formed at current frequency 900 Hz showed the better wear resistance than the others.

关键词： Magnesium alloy Micro-arc oxidation SiC nano-particles Wear resistance