ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    EFFECT OF TEMPERING TEMPERATURE ON LOW TEMPERATURE IMPACT TOUGHNESS OF A LOW CARBON Mn-SERIES BAINITIC STEEL
    GAO Guhui ZHANG Han BAI Bingzhe
    Acta Metall Sin, 2011, 47 (5): 513-519.  DOI: 10.3724/SP.J.1037.2010.00550
    Abstract   PDF (1408KB) ( 2650 )
    In order to reduce the cost of alloying elements, low carbon Mn series bainitic steels have been developed. The effect of tempering temperature on the microstructure and low temperature impact toughness of a low carbon Mn-series steel has been investigated in the present study. The as rolled steel plate samples with 30 mm thickness were tempered from 280 ℃ to 600 ℃ for 2 h. Metallographic microstructure show that the< microstructure of the as-rolled steel is mostly bainite laths. Bainite laths start to merge and broaden after tempering at 460 ℃, and quasi--polygonal ferrite structures could be revealed after tempering at 600 ℃. Compared with the as-rolled steel, after tempering at 460 ℃, the yield strength of the steel changes slightly, remaining 725 MPa, while the Charpy absorbed energy at $-$40 ℃ increases from 38 J to 146 J, and the ductile-brittle transition temperature (DBTT) decreases from -18 ℃ to -48 ℃. The EBSD and TEM results indicate that the improvement of low temperature impact toughness after tempering at 460 ℃ is caused by the increase of fraction of high angle boundaries and the decrease of effective grain size during the recovery process of bainite laths.
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    CORROSION BEHAVIOR OF BRIDGE WEATHERING STEELS IN ENVIRONMENT CONTAINING Cl-
    GAO Xinliang ZHU Miaoyong FU Guiqin WANG Feng DENG Zhiyin
    Acta Metall Sin, 2011, 47 (5): 520-527.  DOI: 10.3724/SP.J.1037.2010.00496
    Abstract   PDF (1534KB) ( 1579 )
    In order to understand the corrosion behavior of bridge weathering steels at marine atmosphere, three type steels containing 3.5% Ni were prepared for alternate wet-dry accelerated corrosion test. Microstructures, rust layer morphologies and characteristics of bridge weathering steels with different Mn and Cu contents at different stages were studied by using optical microscope, XRD and SEM. The results show microstructures of the bridge weathering steels are composed of quasi-polygonal ferrite, acicular ferrite and granular bainite. Corrosion resistance of the steels is improved with Mn content increasing. Distributions of Ni and Mn are uniform inside rust layers, but Cu is enriched at gaps and pores in rust layers. Crystal phases are mainly composed of Fe3O4γ-FeOOH and α-FeOOH in rust layers, however, the compositions are somewhat different at different stages. The formation of γ-FeOOH and α-FeOOH is closely related to the change in corrosion rate. With increasing Mn content, the formation of γ-FeOOH and α-FeOOH are accelerated and their sizes are restrained.
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    EXPERIMENTAL AND MODELING STUDIES ON THE STRUCTURE FORMATION OF HIGH PRESSURE DIE CAST MAGNESIUM ALLOY CONSIDERING THE EXTERNALLY SOLIDIFIED CRYSTALS IN THE SHOT SLEEVE\par
    WU Mengwu XIONG Shoumei
    Acta Metall Sin, 2011, 47 (5): 528-534.  DOI: 10.3724/SP.J.1037.2011.00004
    Abstract   PDF (1365KB) ( 1101 )
    The externally solidified crystals (ESCs) in the shot sleeve have a great influence on the final structure of magnesium alloy during cold-chamber high pressure die casting (HPDC) process. In typical HPDC microstructure, a surface layer with uniformly fine grains and a central region containing a mixture of coarse ESCs and fine grains are commonly observed from the cross section of the castings. In the present work, experiments were conducted to investigate the effects of process parameters on the formation of ESCs in the shot sleeve and the final microstructure of magnesium alloy, especially focusing on the grain size, the morphology and distribution of the ESCs. Based on cellular automaton method, a numerical model was developed to simulate the microstructure evolution of magnesium alloy under HPDC process. According to experimental statistics relating the area fraction of the ESCs, a nucleation model was established in which the ESCs in the shot sleeve were taken into account. Simulations were carried out to predict the microstructure of “step-shape” die castings of AM50 magnesium alloy with different process parameters. It was found that the simulated results were in accordance with the experimental ones.
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    THREE DIMENSIONAL DYNAMICAL MEASUREMENT OF DISTORTION OF HEAVY STEEL CASTINGS DURING HEAT TREATMENT PROCESS
    KANG Jinwu NIE Gang YU Hailiang LONG Haimin HAO Xiaokun HUANG Tianyou HU Yongyi
    Acta Metall Sin, 2011, 47 (5): 535-539.  DOI: 10.3724/SP.J.1037.2010.00617
    Abstract   PDF (929KB) ( 885 )
    At the forced air cooling stage in normalizing process of heavy steel castings, the nonuniform cooling might result in thermal and phase transformation stresses, which might cause the distortion, especially for the heavy yet thin blade castings. Dynamical measurement of the distortion of castings during heat treatment process will be significant for understanding the mechanism of distortion and then taking the control measures in productions. In this paper, a novel measuring method, fixed direction method, was proposed, which could three-dimensionally and dynamically measure the distortion of castings without index points at high temperature, and the corresponding analysis method was established. The method was employed to measure the distortion of a hydro blade casting at the forced cooling stage in normalizing process, and the dynamical distortion behavior in three dimensions of the blade casting was obtained. And the measurement error of blade casting was analyzed. The results show that under the conditions of no index points and high temperature, the three-dimensional distortion of castings could be dynamically measured through the fixed direction method.
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    MICROSTRUCTURE EVOLUTION OF Ni-Sn EUTECTIC ALLOY IN LASER RAPID SOLIDIFICATION
    CAO Yongqing LIN Xin WANG Zhitai YANG Haiou HUANG Weidong
    Acta Metall Sin, 2011, 47 (5): 540-547.  DOI: 10.3724/SP.J.1037.2010.00494
    Abstract   PDF (1241KB) ( 1289 )
    The microstructure evolution of Ni–Sn alloys (Ni–28%Sn, Ni–30%Sn, Ni–33%Sn and Ni–35%Sn) near eutectic during laser rapid solidification has been investigated. In low velocity laser scanning, the microstructures of Ni–28%Sn and Ni–35%Sn hypereutetic alloys consist of refined primary dendritic phase, which is α–Ni phase for the former and Ni3Sn phase for the latter, and (α–Ni+Ni3Sn) eutectic phase. However, the microstructures of Ni–30%Sn and Ni-33%Sn near–eutectic alloys consist completely of (α–Ni+Ni3Sn) eutectic, and they undergo a morphological transition from the columnar to equiaxed eutectic from bottom to the top of molten pool. There is a small amount of residual coarse primary dendritic phase of substrate in the bottom of molten pool for these four Ni–Sn alloys. With increasing laser scanning velocity, compared with the mixed lamella and rod eutectic microstructures in the substrates, for these alloys eutectic in molten pool is completely composed of lamella eutectic, and lamella eutectic spacing is reduced significantly after laser rapid solidification. Besides, lamella eutectic in molten pool grows epitaxially along the normal to the molten pool interface with the substrate. Moreover, the composition range and the critical laser scanning velocity are also obtained for coupled eutectic growth during laser rapid solidification. In the present work, further analysis of microstructure evolution is given by using KGT and TMK models, showing a good agreement between the simulated and the experimental results.
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    EFFECT OF TRAPS ON DIFFUSIVITY OF HYDROGEN IN 20g CLEAN STEEL
    CHEN Yexin CHANG Qinggang
    Acta Metall Sin, 2011, 47 (5): 548-552.  DOI: 10.3724/SP.J.1037.2010.00610
    Abstract   PDF (735KB) ( 1202 )
    Electrochemical permeation experiment is the most common method used in measuring hydrogen diffusivity. Because the effect of hydrogen traps has been ignored, there is a larger deviation between diffusion coefficients of hydrogen given by many investigators, especially at low temperatures. In order to study the effect of hydrogen traps on diffusion coefficient of hydrogen, the permeation current transients were measured by Devanathan-Stachurski cell for the three hydrogen trap states in 20g clean steel in this paper. The first trap state contains the inreversible and reversible hydrogen traps and exists in an original state of the sample. The second trap state contains only the reversible hydrogen traps and exists in the sample treated at 80 ℃ for 3 h after electrochemical permeation experiment. However, the third trap state may not contain any hydrogen traps and exists in the untreated sample after the electrochemical permeation experiment. The electrochemical permeation experiment has been carried out at a constant charging current density (10 mA/cm2) in\linebreak 0.2 mol/L NaOH solution at 30 ℃. The experimental results show that the diffusion of hydrogen in electrochemical hydrogen permeation can be described by a modified equation of diffusion flux versus time in ideal crystal. The modified equation proposed in this paper is $\frac{J_{t}}{J_{\infty}}=\frac{2L}{\sqrt{\pi D(t-t_{0})}}\sum\limits_{n=0}^{\infty}exp
    [-\frac{(2n+1)^{2}L^{2}}{4D(t-t_{0})}]$. The diffusion coefficient and penetration time of hydrogen during electrochemical hydrogen permeation can be obtained directly by using the modified equation to fit the experimental data with a least square method. The experimental results reveal that inreversible hydrogen traps have no effect on the diffusion coefficient of hydrogen, but extend its penetration time. It is also shown that reversible hydrogen traps reduce the diffusion coefficient of hydrogen in 20g clean steel.
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    STUDY ON THE BEHAVIOR OF HYDROGEN IN STEEL HEAT TREATMENT PROCESS WITH PROTON CONDUCTOR SENSOR
    LI Ying DING Yushi HU Jingtao WANG Changzhen
    Acta Metall Sin, 2011, 47 (5): 553-558.  DOI: 10.3724/SP.J.1037.2010.00615
    Abstract   PDF (1013KB) ( 1131 )
    The dehydrogenation behavior in two steels during heat treatment process was investigated by using CaZr0.9In0.1O3-α proton conductor hydrogen sensor and electrochemical impedance spectroscopes of these steels have been measured and analyzed. Based on the changes of hydrogen partial pressure in these steels with temperature and with time at constant temperatures of 600℃ and 800℃, it is found that the dehydrogenation begins only when heat treatment temperature is higher than 600℃. Although this temperature exceeds higher than 727℃, the dehydrogenation behavior is not significantly improved. This means that the reasonable heat treatment temperature is in the range of 600-730℃. The experimental results show that the CaZr0.9In0.1O3-α proton conductor hydrogen sensor could be used to monitor in situ changes of partial hydrogen pressure during dehydrogenation of solid state steels as a suitable sensor.
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    XRD LINE PROFILE ANALYSIS OF LY12 ALUMINUM ALLOY UNDER DYNAMIC COMPRESSIVE EXPERIMENT
    FAN Zhijian SONG Zhenfei XIAO Dawu CHEN Bo
    Acta Metall Sin, 2011, 47 (5): 559-565.  DOI: 10.3724/SP.J.1037.2010.00650
    Abstract   PDF (1002KB) ( 1331 )
    The plastic deformation of metals under dynamic loading is related to the evolution of dislocation structure and density which is thermal activation-dependent. The dynamic compressive experiment on LY12 aluminum alloy has been performed by Hopkinson bar at different temperatures. X-ray diffraction line profile analysis is adopted for the tested specimens to investigate the micro-and/or meso-scale structure evolution. The edge character of dislocations in the specimens was determined by analyzing the integral breadths of X-ray diffraction lines. The Fourier analysis of diffraction lines indicates that under dynamic loading, the dislocation density approaches to saturation rapidly at the initial stage of plastic deformation, dislocations are homogeneously distributed in the specimens. It also demonstrates that the dislocation density decreases with increasing testing temperature. Meanwhile the size of substructures has a tendency of broadening with temperature, especially in the range from 280℃ to 300℃ which corresponds to the temperature of dissolution of precipitated phase in the aluminum matrix.
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    INFLUENCE OF AXISYMMETRIC MAGNETIC FIELD ON MICROSTRUCTURE AND FRICTION PERFORMANCE OF TIN FILM DEPOSITED BY ARC ION PLATING
    XIAO Jinquan LANG Wenchang ZHAO Yanhui GONG Jun SUN Chao WEN Lishi
    Acta Metall Sin, 2011, 47 (5): 566-572.  DOI: 10.3724/SP.J.1037.2010.00686
    Abstract   PDF (1237KB) ( 1138 )
    Arc ion plating (AIP) has been widely used in the deposition of various kinds of thin solid films. In AIP process, cathode spot motion is the key factor because it affects the physical characteristics of arc plasma, the utilization of cathode materials, the ejection of macroparticles (MPs) and the quality of subsequent films. It has been found that the cathode spot can be steered by an external magnetic field, such as an axisymmetric magnetic field (AMF). In this work, a new AMF produced by using an adjustable electromagnetic coil associated with a concentric magnetic flux guider was applied to the cathode surface to deposit TiN films, and it was focused on the influence of the AMF on the content and size of MPs, microstructure and friction performance of TiN films. The results show that the size and number of MPs decrease significantly with the increase in the transverse component of AMF. Meanwhile, the TiN film (111) preferred orientation enhances and its grain size decreases. Furthermore, the friction coefficient of films reduces and the wear resistance of films increases.
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    FIRST-PRINCIPLES STUDY OF STACKING FAULT ENERGY AND DEFORMATION TWIN\par ENERGY IN Al-Mg ALLOYS
    DONG Minghui HAN Peide ZHANG Caili YANG Yanqing ZHANG Lili LI Hongfei
    Acta Metall Sin, 2011, 47 (5): 573-577.  DOI: 10.3724/SP.J.1037.2010.00715
    Abstract   PDF (869KB) ( 1244 )
    By using first--principles method based on the density functional theory (DFT), the stacking fault energy (SFE) and deformation twin energy (DTE) for the (111)[112] slip system of pure Al metal and Al-Mg alloys were investigated. The dependence of these SFE and DTE on solid--solution Mg content and its accupation were specifically analyzed. Two major approximations were made in the process of calculation, which were local density approximation (LDA) and generalized gradient approximation (GGA-PW91), respectively. The calculated SFE values by using GGA-PW91 exhibit an excellent agreement with corresponding experimental measurements. For pure Al metal, the calculated SFE values are greater than those of DTE. Moreover, it is found that under the same deformation conditions, the DTE in pure Al and Al-Mg alloys increase monotonically with the increase of deformation twin thickness. In addition, the calculated results shows that 6-layer twin possesses the lowest DTE, which is probably due to its mirror symmetry structure. Also noteworthy, our calculations reveal a noticeable decreased tendency of SFE and DTE with Mg content increasing, while Mg occupying on stacking fault and twin boundary most likely increases SFE and DTE. There are no considerably detected effects of Mg atomic occupancy variation in Al-Mg alloy on its cohesive energy and formation energy.
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    ISOTHERMAL OXIDATION BEHAVIOR OF A NiCoCrAlYSiB+AlSiY GRADIENT COATING
    WANG Weixin JIANG Sumeng WEI Guangzhi MA Jun GONG Jun SUN Chao
    Acta Metall Sin, 2011, 47 (5): 578-586.  DOI: 10.3724/SP.J.1037.2010.00649
    Abstract   PDF (1787KB) ( 1486 )
    Conventional NiCoCrAlYSiB coating and (NiCoCrAlYSiB+AlSiY) gradient coating were prepared by using arc ion plating (AIP) on the Ni base single crystal superalloy substrate. Comparative studies of the morphology and microstructure together with high temperature oxidation behaviors at 1000, 1100 and 1150 ℃ for the two different coatings were investigated. The results show that after vacuum annealing, the conventional coating is mainly composed of general γ'/γ and a small quantity of β-NiAl dispersed in γ'/γ while the outer layer of the gradient coating consists of β-NiAl and dispersed β-Cr and Cr3Si in β-NiAl and the inner layer consists of Cr-rich phases plus minor β-NiAl. The conventional coating has excellent oxidation resistance only at 1000℃, while it degraded rapidly at 1100 ℃ and 1150 ℃, on which surface spinel formation was observed; however, the gradient coating has more excellent oxidation resistance than the conventional one at all the three temperatures. After oxidation for 300 h at 1100℃, there still exists a great amount of β-NiAl, and even after oxidation for 300 h at 1150℃, Al content is higher than 8% (mass fraction), in which a small amount of β-NiAl and supersaturated γ'/γ insure the formation and self repair of alumina.
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    HOT DEFORMATION BEHAVIOR AND MICROSTRUCTURE EVOLUTION OF A HIGH-Nb-CONTAINING TiAl BASED ALLOY
    WANG Gang XU Lei WANG Yong ZHENG Zhuo CUI Yuyou YANG Rui
    Acta Metall Sin, 2011, 47 (5): 587-593.  DOI: 10.3724/SP.J.1037.2011.00005
    Abstract   PDF (1606KB) ( 1214 )
    The hot deformation behavior of a high-Nb-containing TiAl based alloy has been studied using the processing map approach. Compression tests were conducted in the temperature range of 950-1300 ℃ and the strain rate range of 0.001 s-1  to 10 s-1 on a Gleeble-3800 testing system. The flow stress was found to be strongly dependent on the temperature and the strain rate. The regimes of flow instability have been delineated in the temperature range of 950-1200 ℃ and the strain rate ranges from 1 s-1 to 10 s-1, as well as in the temperature of 1250-1300 ℃ and the strain rate of 10 s-1. The optimal hot-working conditions for the investigated TiAl alloy are in two regimes: (i) in the temperature range 950-1100 ℃ and at the strain rate of 0.001 s-1 to 0.1 s-1, and (ii) in the temperature range 1250-1300 ℃ and at the strain rate of 0.001 s-1 to 1 s-1. The material exhibited dynamic recrystallization to produce a fine-grained microstructure in these conditions. In the temperature range 1150-1200 ℃ with the strain rate 0.001 s-1, the alloy exhibited superplasticity.
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    NUMERICAL SIMULATION OF HYDROGEN INDUCED DELAYED FRACTURE OF AISI4135 HIGH STRENGTH STEEL USING COHESIVE ZONE MODELING
    WANG Yanfei GONG Jianming JIANG Wenchun JIANG Yong TANG Jianqun
    Acta Metall Sin, 2011, 47 (5): 594-600.  DOI: 10.3724/SP.J.1037.2010.00711
    Abstract   PDF (1336KB) ( 1081 )
    High strength steels are susceptible to hydrogen induced delayed fracture (HIDF). A sequential coupling calculation on HIDF of high strength steel was developed based on cohesive zone modeling (CZM) using finite element program-ABAQUS. The calculation procedure contained three steps: elastic plastic stress analysis, stress assisted transient hydrogen diffusion and cohesive stress analysis using hydrogen dependent linear traction-separation law. Using this method, the prediction of fracture time and crack initiation location of pre-charged notched bar of AISI4135 high strength steel was obtained. The effects of stress concentration factor, initial hydrogen content, and tension load were also considered. The results show: (i) predictions of the time to fracture were in good quantitative agreement with the experimental results; the hydrogen dependent cohesive zone modeling can be used in prediction of failure in actual structures; (ii) crack initiation occurs when a critical hydrogen concentration at the location of stress peak is reached by accumulation, the critical hydrogen concentration is dependent on stress concentration factor and tension load, but independent of initial hydrogen content; (iii) as one of the three parameters mentioned above decreasing, the fracture initiation time and the critical hydrogen\linebreak concentration increase.
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    STUDY ON THERMAL FATIGUE FAILURE OF THIN GOLD FILM WITH ALTERNATING CURRENT LOADING
    WANG Ming ZHANG Bin LIU Changsheng ZHANG Guangping
    Acta Metall Sin, 2011, 47 (5): 601-604.  DOI: 10.3724/SP.J.1037.2010.00668
    Abstract   PDF (817KB) ( 1088 )
    Metallization interconnects in microelectronic integrated circuits usually fail during fabrication and long-term service under electrical, mechanical, or thermal field and coupled multi-field of them, such as electromigration (EM) failure induced by direct current, stress-induced voiding (SIV) damage and thermal fatigue under thermal cyclic strain, which affect the reliability of the interconnects. Although EM and SIV have been actively investigated for several decades, there is limited work on thermal cyclic strain-induced thermal fatigue behaviors of thin metal films, which are becoming a more and more important reliability issue. In this work, the failure behavior of the 200 nm-thick Au thin films was studied through applying thermal cyclic strain generated by alternating current. The total thermal cyclic strain was determined from the temperature distribution along the Au line with a width of 6 μm according to the experiment measurement and theoretical calculation. It was found that the grain size in the Au thin films increased inhomogenously and the damage along grain boundaries resulted in the fatal failure of the Au line in the condition of Δε≦0.35% after 5$\times$10$^{6}$ cyc. Based on the experimental observations, thermal fatigue and mechanical fatigue failure behaviors were analyzed comparatively, and the basic mechanisms were discussed.
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    CRACK PROPAGATION AND DOMAIN SWITCHING IN BaTiO3 SINGLE CRYSTALS UNDER EXTERNAL FIELD
    JIANG Bing XING Xianran GUO Zhimeng
    Acta Metall Sin, 2011, 47 (5): 605-610.  DOI: 10.3724/SP.J.1037.2010.00665
    Abstract   PDF (767KB) ( 869 )
    Domain switching and crack propagation in BaTiO3 single crystal under external field were in-situ observed by polarized light microscopy (PLM). It was found that under mechanical field, domain-switching bands appear around the crack tip to relax stress and domain switching occurred before crack propagation. Under electric field, the internal stress induced by domain switching results in crack propagation.
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    EFFECT OF THE CROSS-INTERACTION ON THE FORMATION AND EVOLUTION OF INTERMETALLIC COMPOUNDS IN Cu(Ni)/Sn-Ag-Cu/Cu(Ni) BGA STRUCTURE SOLDER JOINTS
    LI Xunping ZHOU Minbo XIA Jianmin MA Xiao ZHANG Xinping
    Acta Metall Sin, 2011, 47 (5): 611-619.  DOI: 10.3724/SP.J.1037.2011.00063
    Abstract   PDF (1606KB) ( 1507 )
    The formation and evolution of interfacial intermetallic compounds (IMCs) in Cu(Ni)/Sn-3.0Ag-0.5Cu/Cu(Ni) BGA (Ball Grid Array) structure solder joints both in the as-reflowed state and undergoing isothermal aging at 125℃ were investigated. The results show that there exists a significant cross-interaction effect of the solder pad/under bump metal (UBM) on the composition, morphology and growth kinetics of interfacial IMCs in solder joints. The reactions of solder/Ni UBM strongly depends on the Cu content of the solder, for a high Cu content, a continuous (Cu, Ni)6Sn5 layer forms at the interface, while for a low Cu content, a continuous (Ni, Cu)3Sn4 layer appears at the interface. The cross-interaction of Cu and Ni in Cu/Sn-3.0Ag-0.5Cu(SAC)/Ni solder joints has obvious influence on the composition and morphology of the interfacial IMC; and the IMC spalling phenomenon occurs at the interface of Ni side. During isothermal aging at 125℃, the growth rate constant of the interfacial IMC layer in SAC/Cu and Cu/SAC/Cu joints increases with the Cu concentration, and the cross-interaction of Cu and Cu decreases the interfacial IMC growth rate constant at once-reflowed Cu side. However, both of the cross-interactions of Cu-Ni and Ni-Ni increase the growth rate constant of the interfacial IMC at once-reflowed Ni side and Ni has a greater influence than Cu. The cross-interaction of Cu and Ni is beneficial for suppression of growth of Cu3Sn and reduction the growth rate of IMC at Cu side, while having no significant influence on the porosity of Kirkendall voids in Cu3Sn layer at Cu side of the joint.
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    SIMULATION OF NH4Cl-H2O DENDRITIC GROWTH IN DIRECTIONAL SOLIDIFICATION
    SHI Yufeng XU Qingyan GONG Ming LIU Baicheng
    Acta Metall Sin, 2011, 47 (5): 620-627.  DOI: 10.3724/SP.J.1037.2010.00642
    Abstract   PDF (1294KB) ( 1571 )
    Studying the microstructure evolution mechanism of directional solidification by numerical simulation has the directive significance in the solidification theory and practical production. Taking account of constitutional undercooling, curvature undercooling, preferred growth orientation coefficient, temperature gradient and pulling velocity, a modified cellular automaton (MCA) model has been developed to simulate the influence of different temperature gradient directions, different preferred growth orientations and different pulling velocities on the morphologies of columnar dendrites. The simulation results well describe the influence of inclination angle between temperature gradient and growth direction on primary dendrite arm spacing (PDAS). Meanwhile the simulation results also reproduce the competitive growth of columnar dendrites with different preferred growth orientations and the splitting of the columnar dendritic tips. For the purpose of verifying this model, the relevant experiments have been carried out on an NH4Cl-H2O solution. The experimental results are compared critically with the simulation ones from the MCA model.
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    COMPOSITION OPTIMIZATION OF Al-Mg-B THIN FILM PROPERTIES PREPERAED BY MAGNETRON SPUTTERING
    QU Wenchao WU Aimin WU Zhanling BAI Yizhen JIANG Xin
    Acta Metall Sin, 2011, 47 (5): 628-633.  DOI: 10.3724/SP.J.1037.2010.00712
    Abstract   PDF (1002KB) ( 920 )
    Aluminum magnesium boron ternary boride (AlMgB14) possesses high hardness, high-temperature oxidation resistance, high temperature corrosion resistance, low density, low friction and other excellent properties, and could be widely used in tool, mold, micro-mechanical manufacture and aerospace, et al. In this paper, Al-Mg-B films have been prepared by multi-target (high pure aluminum, magnesium and boron targets) magnetron sputtering on the silicon (100) substrate at room temperature. The films with an atomic ratio of Al∶Mg∶B=1∶1∶14 were obtained by controlling the sputtering power and the volume ratio of Al/Mg co-target. X-ray diffraction (XRD) and High resolution transmission electron microscopy (HR-TEM) test results show that all the as-deposited films are amorphous. The X-ray photoelectron spectroscopy (XPS) results showe that there are some B-B and Al-B single bond in the as--deposited films, and the Fourier transform infrared spectroscopy (FTIR) tests indicate further that the films possess B12 icosahedra structure. The hardness of the films as shown by nano indentor test will be increasing with the increase of content of B around B-AlMg isoelectronic line and close to boron--rich side, and up to 32 GPa with low friction coefficients of 0.06-0.08.
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    PREPARATION OF SEMISOLID 5052 ALUMINUM ALLOY SLURRY BY INDIRECT ULTRASONIC VIBRATION
    LU Shulin WU Shusen DAI Wei AN Ping MAO Youwu
    Acta Metall Sin, 2011, 47 (5): 634-640.  DOI: 10.3724/SP.J.1037.2010.00552
    Abstract   PDF (1695KB) ( 1219 )
    A new indirect ultrasonic vibration (IUV) apparatus was employed to prepare semisolid 5052 aluminum slurry. The effects of IUV temperature and time on the morphology of the semisolid slurry were studied. The results indicate that semisolid slurry with fine and globular primary grains can be obtained by applying IUV from the liquidus temperature (643℃) of this alloy or a higher temperature for about 50 s. When IUV is applied through the bottom of the metal cup at 643℃, a lot of nuclei form near the bottom of metal cup and these nuclei grow into globular grains. In this stage, the average diameter of primary grains decreases as IUV time increased up to 30 s and then it increases with further increasing of IUV time from 30 s to 60 s, and the average shape coefficient of primary grains increases as IUV time increased. When the IUV is applied at 640℃, dendrites can be broke up and a mixture structure consisted of rosette and globular grains with a average diameter of 105 μm is obtained.
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