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Microstructure and formation mechanism of twins of laths of austenite with high nitrogen

science china(Technological sciences) 2007年第6期50卷 755-764页

作者： WU CuiLan1,2.& LUO ChengPing2.1 Center for High Resolution Electron Microscopy, college of materials {2. and engineering, Hunan university, Changsha 410082. china 2.college of Mechanical engineering, South china university of technology, Guangzhou 510641, china 1. Center for High Resolution Electron Microscopy College of Materials Science and Engineering Hunan University Changsha 410082 China 2. college of Mechanical engineering South China University of Technology Guangzhou 510641 China

The microstructure of composite diffusion layer of the nitrided and chromized 0.2. carbon steel is investigated using TEM and EDS. It is found that laths of austenite with high nitrogen (γ N) precipitate from α-ferrite matrix in the deeper zone of the diffusion layer. These γ N laths are all twins, with their {111} twinning planes parallel to the lath axis, thus forming a characteristic "back-to-back" morphology. There are two types of γN lath. The first is a genuinely {111} twin, and γ N and α keep the accurate K-S relationship, and each γ N and α form a sharp and smooth γ N/α inter- face of {335}γN//{341}α, namely habit plane {335}fcc. The second is a pseudo-twin, with micro-twins {111} or faults formed within the two twin components. Localized lattice deformation (relaxation) seems to have occurred at the interfaces of the second type of γ N due to the formation of micro-twins or faults within the twin components. These micro-twins or faults make the orientation relationship (OR) between each of the γN and the α-matrix deviate from the accurate K-S OR, and the OR between two γ N twin components deviate from the genuine {111} twin relation- ship. In addition, the γ N/α interface of the second type of γ N is not as sharp or smooth as that of the first one.

关键词： austenite containing nitrogen, twins, steel 2., nitriding, composite chromizing

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High-temperature oxidation behavior of Al_2._3/TiAl matrix composite in air

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science china(Technological sciences) 2009年第5期52卷 1273-1282页

作者： AI TaoTao1,WANG Fen2.& FENG XiaoMing1 1 Department of materials science and {2.,Shaanxi university of technology,Hanzhong 72.003,china 2.School of materials science and {2.,Shaanxi university of science and technology,Xi’an 71002.,china 1. Department of materials science and {2. Shaanxi University of Technology Hanzhong 723003 China 2. School of materials science and {2. Shaanxi University of Science and Technology Xi’an 710021 China

The oxidation behavior of Al2.3/TiAl in situ composites fabricated by hot-pressing technology was in-vestigated at 900℃ in static *** results indicate that the mass gains of the composites samples decrease gradually with increasing Nb2.5 content and the inert Al2.3 dispersoids effectively increase the oxidation resistance of the *** higher the Al2.3 dispersoids content,the more pro-nounced the *** primary oxidation precesses obey approximately the linear laws,and the cyclic oxidation precesses follow the parabolic *** oxidized sample containing Ti2.lN and TiAl phases in the scales exhibits excellent oxidation *** oxide scale formed after exposure at 900 ℃ for 12. h is multiple-layered,consisting mainly of an outer TiO2.layer,an intermediate Al2.3 layer,and an inner TiO2.Al2.3 mixed *** the outer layer to the inner layer,TiO2.Al2.3 mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed *** the substrate,cross-section micrograph shows a relatively loose layer,and micro-and macro-pores remain on this layer,which is a transition layer and transferres from Al2.3+TiO2.scale to *** thickness of oxide layer is about 2. μ*** is also found that continuous protective alumina scales can not be observed on the surface of oxida-tion *** ions diffuse outwardly to form the outer TiO2.layer,while oxygen ions transport inwardly to form the inner TiO2.Al2.3 mixed *** long-time intensive oxidation exposure,the internal Al2.3 scale has a good adhesiveness with the outer TiO2.*** obvious spallation of the oxide scales *** increased oxidation resistance by the presence of in situ Al2.3 particulates is at-tributed to the enhanced alumina-forming tendency and thin and dense scale ***2.3 particu-lates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface,thereby the TiO2.growth rate decreases,which is also beneficial to improve the oxidation resistance.

关键词： Al2.3/TiAl matrix composite oxidation resistance high temperature

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Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

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Rare Metals 2010年第1期29卷 86-91页

作者： CHU Ke, JIA Chengchang, LIANG Xuebing, and CHEN Hui School of materials science and {2., university of science and technology Beijing, Beijing 100083, china School of materials science and {2. University of Science and Technology Beijing

Two powder mixing processes, mechanical mixing （MM） and mechanical alloying （MA）, were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering （SPS） to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2.h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2.h demonstrated high relative density and an excellent thermal conductivity of 32. W.m^-1.K^-1, owing to its having few defects and strong inter-facial bonding.

关键词： metal matrix composites thermal properties sintering powder mixing

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Effect of surfactants on the structure and photoelectric properties of ITO films by sol-gel method

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Rare Metals 2010年第2期29卷 143-148页

作者： LIU Jiaxiang, WU Da, ZHANG Nan, and WANG Yue college of materials {2. and engineering, Beijing university of Chemical technology, Beijing 10002., china college of materials {2. and engineering Beijing University of Chemical Technology

The Indium tin oxide（ITO） thin film possesses excellent photoelectric properties that enable it to act as an ideal transparent *** obtain high-quality ITO films through sol-gel method, the ionic surfactant monoethanolamine and the non-ionic surfactant polyethylene glycol（PEG） were added to the ITO precursor *** influences of surfactants on the structural and photoelectric properties of ITO film samples were *** patterns indicated that surfactant monoethanolamine contributed to film predominant grain orientation along the（400） *** high transmittance（over 95%） was attributed to the preferred orientation and the grain size expansion of ITO *** showed that the surface particle size and the morphology of ITO films were strongly dependent on the kind of surfactants *** to the shortwave region, the absorption edge of the films exhibited the Burstein-Moss shift.

关键词： surfactants indium tin oxide films sol-gel structure photoelectricity

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Three-dimensional elasticity solution of simple-supported rectangular plate on point supports, line supports and elastic foundation

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science china(Technological sciences) 2009年第3期52卷 584-589页

作者： XU YePeng1 & ZHOU Ding2.1 School of science, Nanjing university of science and technology, Nanjing 2.0094, china 2.college of Civil engineering, Nanjing university of technology, Nanjing 2.0009, china 1. School of science Nanjing University of Science and Technology Nanjing 210094 China 2. college of Civil engineering Nanjing University of Technology Nanjing 210009 China

This paper studies the bending of simple-supported rectangular plate on point supports, line supports and elastic foundation. On the basis of three-dimensional elasticity theory, the exact expressions of the displacement functions, which satisfy the governing differential equations and the simply supported boundary conditions at four edges of the plate, are analytically derived. The reaction forces of the in- termediate supports are regarded as the unknown external forces acting on the lower surface of the plate. The unknown coefficients are then determined by the boundary conditions on the upper and lower surfaces of the plate. Comparing the numerical results obtained from the proposed method to those obtained from Kirchhoff plate theory, Mindlin plate theory and those obtained from the commer- cial finite element software ANSYS, the high accuracy of the present method has been demonstrated.

关键词： rectangular plate point support line support elastic foundation displacement stress three-dimensional elasticity solution

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Sliding Mode Control with Disturbance Observer for a Class of Nonlinear Systems

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International Journal of Automation and computing 2012年第5期9卷 487-491页

作者： Lei-Po Liu Zhu-Mu Fu Xiao-Na Song college of Electric and Information engineering,{2., luoyang 4.1003. china 1. college of Electric and Information engineering Henan University of Science and Technology Luoyang 471003 China

This paper is concerned with the stabilization problem for a class of nonlinear systems with disturbance. The disturbance model is unknown and the first derivative of disturbance is bounded. Firstly, a general disturbance observer is proposed to estimate disturbance approximatively. Secondly, since the bound of the disturbance observer error is unknown, an adaptive sliding mode controller is designed to guarantee that the state of system asymptotically converges to zero and the unknown bound can be adjusted by an adaptive law. Finally, an example is given to illustrate the effectiveness of the proposed method.

关键词： Nonlinear systems disturbance observer adaptive sliding mode control derivative of disturbance asymptotic stability

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Numerical Simulation of Solidification Microstructure and Effects of Phase-field Parameters on Grain Growth Morphologies

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Journal of materials science & {2. 2005年第6期21卷 921-924页

作者： Jingfeng LIU+, Ruixiang LIU and Liliang CHEN Research Studio of Solidification Simulation, college of materials {2. and engineering, Huazhong university of {2. and technology, Wuhan 430074, china Research Studio of Solidification Simulation College of Materials Science and Engineering Huazhong University of Science and Technology Wuhan 430074 China

By a simple phase field model, a series of numerical simulations of solidification microstructure was performed to show a rich variety of dendritic patterns. At the same time, the relation between the morphology of grain growth and some parameters including the strength of anisotropy, dimensionless latent heat and the size of initial solid zone was studied. It is for the first time that patterns of grain growth were associated with the size of initial solid zone, which is an interesting issue. The possible reason for this may be that variation in the size of initial solid zone may bring about fluctuation of the interface energy, making the interface unstable.

关键词： Phase-field model Dendritic pattern Simulation

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Predicting Equation for Adjusting Glass Temperature of Binder Used for P/M Warm Compaction Processing

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International Journal of Minerals,Metallurgy and materials 1998年第1期12卷 39-40页

作者： Shiju Guo Tao Lin Mingyi Li (materials science and {2. School, university of science and technology Beijing, Beijing 100083, china) materials science and {2. School University of Science and Technology Beijing Beijing 100083 China

Based on considering both negative effect of compacting pressure on glass temperature (Tg) and positiveeffect of plasticizer added into organic binder, a mathematical equation for adjusting Tg of binder used for warmcompaction processing is given. The equation shows that mass fraction of plasticizer need for lowering Tg is function of compacting plessure. The rationality of the equation for warm compaction processing is also discussed.

关键词： warm compaction binder glass temperature

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Properties of meso-tetrakis (4-n-alkanoyloxyphenyl) porphyrin liquid crystal Co and Ni complexes

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science china Chemistry 2007年第4期50卷 488-493页

作者： LIU Wei1,2.& SHI TongShun2.1 college of materials {2. and engineering, Shandong university of technology, Zibo 2.5049, china 2.Department of Chemistry, Jilin university, Changchun 13002., china 1. college of materials {2. and engineering Shandong University of Technology Zibo 255049 China 2. Department of Chemistry Jilin University Changchun 130023 China

Six series of meso-tetrakis (4-n-alkanoyloxyphenyl) porphyrin Co and Ni complexes (12.kinds) were reported. Nine of the compounds were found to exhibit liquid crystal properties and display a hexagonal columnar discotic columnar (Colh) phase. Molecular structure of all synthesized compounds was confirmed by IR, UV, MS, 1H NIVR, and elemental analysis. These liquid crystalline compounds have been studied by cyclic voltammetry, luminescence, and surface photovoltage spectroscopy.

关键词： porphyrin liquid crystal cyclic voltammetry luminescence surface photovoltage spectroscopy

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Microstructure and Mechanical Properties of Magnesium Alloy AZ31B Brazed Joint Using a Zn-Mg-Al Filler Metal

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Journal of materials science & {2. 2010年第8期26卷 743-746页

作者： Li Ma, Dingyong He, Xiaoyan Li and Jianmin Jiang college of materials {2. and engineering, Beijing university of technology, Beijing 10012., china [a] college of materials {2. and engineering Beijing university of technology Beijing 10012. china

In order to join the similar magnesium alloy, a novel Zn-Mg-Al filler metal was designed and applied to braze AZ31B plates by using high-frequency induction brazing technique. The microstructure, phase constitution and fracture morphology of the brazed joint were investigated. The experimental results show that MgZn2.phase in the original filler metal is completely consumed in the brazing process. Moreover, α-Mg solid solution and α-Mg＋MgZn eutectoid structure formed in the brazing region due to the intensive alloying between the molten filler metal and the base metal in the brazing process. Test results indicate that the shear strength of the brazed joint is 56 MPa. The fracture morphology of the brazed joint shows intergranular fracture mode, where crack originates from the hard α-Mg＋MgZn eutectoid structure.

关键词： Filler metal Brazing Microstructure Mechanical properties

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