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

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    MEASUREMENT OF THE NON-SPHERE SUPERPLASTIC FREE BULGING
    SONG Yuquan MA Pinkui GUAN Zhiping
    Acta Metall Sin, 2010, 46 (1): 1-5. 
    Abstract   PDF (928KB) ( 1232 )

    Superplastic bulging is important technology for forming thin walled workpieces with shell shape. Especially, the compound technology of superplastic bulging and diffusion bonding, by which scores of parts or even more than one hundred parts could be combined to become a assembly, would reduce the weight of the assembly, raise its rigidity and make its structure more reasonable. So, superplastic bulging forming technology plays an important role in the field of aviation manufacturing application. Superplastic free bulging test provides important foundation for establishing mechanical theory of superplastic bulging and it also is a necessary process for superplastic bulging forming due to no die and no effect of friction. Aimed at the problems  coming from precisely measuring the geometry parameters of the axisymmetric surface of revolution which is the real shape of free bulging during the experiment, a vision measure way and its principle are brought forward to detect the edge of sample in the paper. The components of monocular vision system and the method of the camera calibration are introduced. The error compensation equation was deduced through analysis on the vision measure process of the revolution surface. In order to ensure the system in real--time, the algorithm of digital image processing adopted during the experiment is different with that after the experiment, which used sub--pixel arithmetic to improve the measure precision. And then the causes of the error are investigated.

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    SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF Sn0.35-0.5xCo0.35-0.5xZnxC0.30 COMPOSITE
    YANG Shaobin,SHEN Ding,LI Qiang
    Acta Metall Sin, 2010, 46 (1): 6-12. 
    Abstract   PDF (1218KB) ( 1369 )

    A series of Sn0.35-0.5xCo0.35-0.5xZnxC0.30(x=0, 0.05, 0.10, 0.15, 0.20) composites as novel anode materials used in lithium-ion batteries were synthesized from Sn, Co, Zn element powders and carbon black using solid-state sintering and ball milling, and the influences of Zn content on the structures and the electrochemical properties of those materials were analyzed. XRD data of the sintered powders illustrated that minor amount phase CoSn2 is formed firstly in the CoSn matrix phase with increasing content of Zn. Then, a little amounts of Co3Sn2, Zn and Sn are also precipitated. Most of Zn atoms dissolve into CoSn phase and lead to lattice distortion of the matrix. As a result, the lattice parameters a, c and unit cell volume V of CoSn phase are all reduced first and then enlarged with increasing content of Zn. Electrochemical analysis showed that the initial discharge capacity and initial charge-discharge efficiency are both improved first and then tended to stablility with increasing content of Zn, and as x=0.15, reach the maximums, 343 mA-h/g and 73.8%, respectively. The reversible capacity remains above 87.6% of the initial discharge capacity after 25 charge-discharge cycles. The lattice distortion caused by Zn solution and the formation of multiphase are beneficial for accelerating the diffusion of Li+ and enhancing the stability of structure, so the electrochemical properties are improved significantly. The sintered powder Sn0.275Co0.275Zn0.15C0.30 was milled for different times (t=10, 20 and 30 h), and it is shown that the refinements of grains and particles improved discharge capacity obviously, however, charge-discharge efficiency and cycle performance changed little.

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    STRUCTURE AND OPTICAL PROPERTIES OF HIGH-RATE LOW-TEMPERATURE GROWN TiO2 THIN FILMS BY REACTIVE MAGNETRON SPUTTERING
    LI Zhuguo MIYAKE Shoji
    Acta Metall Sin, 2010, 46 (1): 13-18. 
    Abstract   PDF (1202KB) ( 1220 )

    TiO2 thin films have been deposited on unheated glass substrates by an inductively coupled plasma (ICP) assisted direct current (dc) reactive magnetron sputtering. XRD, TEM and UV-Vis spectrophotometer have been used to characterize the films. It is shown that the addition of an ICP and the change of gas input strongly affect film growth and structure. High quality anatase phase TiO2 film has been prepared at the metallic mode of sputtering and at low deposition temperature by using the ICP assisted dc reactive magnetron sputtering and creating a gradient of oxygen favoring the oxidation of the growing film. This film is quite transparent in the visible region, and its refractive index n and the extinction coefficient K at 550 nm are 2.51 and 7.8×10-4, respectively.

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    DYNAMIC RECRYSTALLIZATION OF FERRITE IN A MEDIUM-CARBON STEEL WITH TEMPERED MARTENSITE STRUCTURE DURING HOT DEFORMATION
    LI Longfei, XIA Yangqing, SUN Zuqing, YANG Wangyue
    Acta Metall Sin, 2010, 46 (1): 19-26. 
    Abstract   PDF (1797KB) ( 1402 )

    For plain carbon steels, the microduplex (α+θ) structure consisting of ultrafine ferrite matrix and dispersed cementite particles demonstrates a good balance between strength and ductility as compared with a normal microstructure, e.g. ferrite plus pearlite in hypoeutectoid steels or pearlite in eutectoid steels etc.. Various thermo-mechanical treatments have been developed to obtain such microduplex (α+θ) structure. It is commonly considered that the formation of fine equiaxed ferrite grains during thermo-mechanical treatments involving hot (warm) deformation could be attributed to dynamic recrystallization (DRX) of ferrite. However, the mechanism of DRX of ferrite during the formation of the microduplex (α+θ) structure as well as the effect of cementite particles on DRX of ferrite are still not well understood. In the present work, DRX of ferrite in a medium-carbon steel with different tempered martensites was investigated by hot uniaxial compression tests at 0.01 s-1 and 700 ℃, and the effect of cementite particles with different initial states was analyzed. The results indicate that during hot deformation the coarsening of cementite particles and DRX of ferrite took place, leading to the formation of the microduplex (α+θ) structure. In comparison with static tempering, the diffusions of Fe atoms and C atoms were enhanced by hot deformation and thus the coarsening kinetics of cementite particles was accelerated by 2-3 orders of magnitude. During hot deformation the sizes of cementite particles at the boundaries of ferrite grains increased and the amount of cementite particles in ferrite grains decreased. The former is beneficial to the particle stimulated nucleation under coordinated effects of several particles, and the later can reduce the drag effect of cementite particles on the migration of grain boundaries, both of them are advantageous to DRX of ferrite. With the decrease in the size of cementite particles in the initial microstructures, the critical strain for DRX of ferrite increased, but the resultant microduplex ($\alpha+\theta$) structure is fine, and more uniform.

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    EFFECTS OF ROTARY-DIE ECAP ROUTES ON MICROSTRUCTURE AND MECHANICAL PROPERTY OF AZ31 MAGNESIUM ALLOY
    YAN Kai SUN Yangshan BAI Jing XUE Feng
    Acta Metall Sin, 2010, 46 (1): 27-33. 
    Abstract   PDF (1364KB) ( 1535 )

    Using a 3D rotary-die equal-channel angular pressing (3D-RD ECAP) mold, the commercial wrought magnesium alloy AZ31 has been processed through 4 routes(A', BA', BC' and C') and microstructures as well as mechanical properties of the samples processed were investigated. The results reveal that all the 4 routes can refine microstructures of the alloy, however, the effects on microstructural homogeneity and tensile elongations of the samples are different. The grain sizes of the samples processed through routes A' or BA' are more uniform and their tensile elongations at ambient temperature are also higher than those through BC' or C' routes. The distributions of hardness on the central longitudinal planes of samples extruded through different routes are well consistent with the microstructural characters at the corresponding positions. Strain analysis on the cubic elements in the samples reveals the limitation of the traditional shear mode for ECAP. Based on experimental results and finite element method (FEM) simulation, the deformation homogeneity caused by ECAP processing is closely related to the alternative action of tensile and compressive stresses at the different positions in the samples and is independent of the deformation regularity of the cubic elements in the shear model proposed in the previous studies.

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    STUDY ON W GRADED DOPING DLC COMPOSITE FILMS WITH MULTICOMPONENT TRANSITION LAYER
    YANG Yiyong PENG Zhijian FU Zhiqiang WU Sudong CHEN Xinchun WANG Chengbiao
    Acta Metall Sin, 2010, 46 (1): 34-40. 
    Abstract   PDF (1294KB) ( 1449 )

    W graded doping diamond-like carbon (DLC) composite films with multicomponent transition layer were deposited onto silicon, high speed steel and/or stainless steel wafers using ion beam assisted mid-frequency unbalanced magnetron sputtering technique, and the influences of W target current on the composition, structure and properties of the DLC films were investigated. With increasing W target current, the contents of W and its carbides in the films increase, but the contents of sp3 structure decrease. Although there might be some metal droplets on the surface of the as-prepared samples, the distribution of each element is basically homogenous over the whole surface, and the roughness of sample keeps quite low value, which is in the range of 7.56-15.8 nm. The nanohardness (H), elastic modulus (E), and their ratio, H/E, increase with increasing W target current. The critical loads in scratch test of the as-prepared samples increase with the increase of W target current and are in the range of 80-100 N, indicating very strong adhesions between the films and substrates. Under ambient circumstance, the friction coefficients of the coated samples increase but the wear rates decrease obviously.

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    DESIGN AND PREPARATION OF IN SITU Pb-RICH PARTICLES/Al BASE METALLIC GLASS MATRIX COMPOSITE
    HE Jie LI Haiquan XING Chengrao ZHAO Jiuzhou
    Acta Metall Sin, 2010, 46 (1): 41-46. 
    Abstract   PDF (996KB) ( 1117 )

    The typical Al-Pb immiscible alloy and the additional elements Ni, Y and Co were selected, and a new Al82.87Pb2.5Ni4.88Y7.8Co1.95 multicomponent immiscible alloy has been designed. The ribbon samples of the multicomponent alloys were prepared by rapidly quenched method. The microstructure characterization, thermal stability and formation of composite microstructure have been investigated. The results indicate that the single-phase alloy melt separates into AlNiYCo-rich and Pb-rich liquids during cooling through the miscibility gap. Subsequently, the separated AlNiYCo-rich and Pb-rich liquids solidify into Al-based glassy matrix and crystalline Pb-rich phase, respectively. The crystalline Pb-rich phase in form of spheres is homogeneously embedded into the Al-based metallic glass matrix. Based on the mechanism of the liquid-liquid phase transformation in the miscibility gap of the multicomponent immiscible alloy, a new method has been developed to produce in situ crystalline spheres embedded into the metallic glass matrix by rapid solidification.

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    MICROSTRUCTURAL\, EVOLUTION OF Mn-Si-Cr MEDIUM CARBON STEEL DEFORMED UNDER UNDERCOOLED AUSTENITE STATE
    ZHANG Han BAI Bingzhe
    Acta Metall Sin, 2010, 46 (1): 47-51. 
    Abstract   PDF (964KB) ( 1249 )

    An appropriate deformation with low strain rate was applied to a Mn-Si-Cr medium carbon steel at undercooled austenite state. The deformation promotes the formation of pro--eutectoid ferrite, but no lamellar pearlite was observed during deformation. The ferrites nucleate at the grain boundary of austenite and inside the austenite grains, grow in nearly equiaxial shape, and finally divide austenite and connect with one another, leading to the formation of carbon-rich austenite zones. With the increase of strain, ferrites can continue to nucleate inside carbon-rich austenite zones, grow and connect so that the carbon-rich austenite zones are divided continuously and their carbon concentration becomes higher. When the carbon concentration is enough high, the prime spheroidized carbides with 0.5-1 μm in diameter begin to precipitate at the edge of carbon-rich austenite zones. The dynamic recovery and recrystallization of ferrite during deformation process make carbon atoms escape from the Cottrell atmosphere, resulting in precipitation of the secondary spheroidized carbides with size of several decade nanometers within ferrite grains.

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    HOT DEFORMATION BEHAVIOR OF 2205 DUPLEX STAINLESS STEEL
    CHEN Lei WANG Longmei DU Xiaojian LIU Xiao
    Acta Metall Sin, 2010, 46 (1): 52-56. 
    Abstract   PDF (941KB) ( 1927 )

    During hot deformation of the duplex stainless steels consisting of $\delta$--ferrite and $\gamma$--austenite, their microstructure evolution and mechanical response are more complicated as compared with those of single--phase ferritic or austenitic stainless steels, especially for study of the mechanical behavior. In the present research, the hot deformation behavior of a 2205 duplex stainless steel has been investigated through uniaxial compression test using Gleeble--3800 thermal--mechanical simulator within the temperature range of 1223---1523 K and the strain rate range of 0.01---10 s$^{-1}$, the corresponding flow curves and their characters and microstructures have been determined and analyzed. Elongated austenite distributes in ferrite matrix, and the volume fraction of ferrite increases with rising temperature. Dynamic recrystallization of austenite is enhanced by increasing temperature and decreasing strain rate. Based on the constitutive equation for hot deformation, the apparent activation energy (Q) and the apparent stress exponent (n) of the steel are obtained to be about 451 kJ/mol and 4.026, respectively. There is a particular shape of flow curves, i.e. a yield point elongation-like effect, which is characterized by a non-strengthening plateau during the initial stages of plastic deformation. This yield point elongation-like effect increases with decreasing Zener-Hollomon parameter, Z. When used a simplified stress function, a deviation of linear relationship between ln Z and peak stress (σp) occurred at the critical value (ln Zc=38.18). Relationships between peak stress and temperature and strain rate can be more simply described as σp=20.6ln ε+1118002/T-266.8(ln Z>38.18), and σp=9.1ln ε+493874/T-701.9(ln Z≦38.18).

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    BEHAVIOR AND MECHANISM OF HOT WORK-HARDENING FOR 316L STAINLESS STEEL
    SONG Renbo XIANG Jianying HOU Dongpo REN Peidong
    Acta Metall Sin, 2010, 46 (1): 57-61. 
    Abstract   PDF (1005KB) ( 2115 )

    The characteristics of hot work-hardening for 316L stainless steel have been systematically studied through high temperature compression tests on the Gleeble-1500 thermal simulation testing machine. According to Ludwik true stress-strain model, the experimental data has been regressed by using nonlinear fitting method, and the $n$ value in Ludwik model, a comprehensive index which reflects the competitive result between work-hardening and softening, has been calculated with Crussard-Jaoul method. The dynamic recrystallization and twinning were observed by OM and TEM. The experiments reveal that 316L stainless steel is easy to work-hardening during hot deformation, and deformation rate can effect nC-J-ε curves and variation law; There is no peak stress on its true stress-strain curves, but partial dynamic recrystallization has occurred during hot working process. This incomplete softening mechanism can't counteract the effect of hot work-hardening, so the true stress-strain curves still rise with deformation increasing; In addition, twinning occurred during hot working is one of the major mechanisms of hot work-hardening.

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    STUDY ON LOW TEMPERATURE TOUGHNESS IMPROVEMENT OF WELDING COARSE GRAIN ZONE OF HULL STEELS BY Ti TREATMENT
    YANG Yinhui CHAI Feng YAN Biao SU Hang YANG Caifu
    Acta Metall Sin, 2010, 46 (1): 62-70. 
    Abstract   PDF (1740KB) ( 1326 )

    The welding thermal simulation experiments were carried out on Ti/Al treated steels with different heat inputs by using Gleeble 1500D. The oxide inclusions and microstructures in the two base metals and simulated coarse grain heat affected zones (CGHAZ) were studied by using OM, SEM and EDS. At a higher heat input of 50 kJ/cm the low temperature Charpy impact energy in the CGHAZ of Ti treated steel (TTS) is higher than that of Al treated steel (ATS), and the impact energy of TTS reaches 60 J when the welding heat input was 75 kJ/cm. The dispersed Ti oxide inclusion with good high temperature stability in TTS can promote the nucleation of intragranular ferrite, and the welding heat input of 75 kJ/cm has only little effect on the morphology, composite and size of the inclusion. Whereas the Ti-rich nitride precipitated at the core of Al2O3 dissolved at high temperature, which can't promote acicular ferrite nucleation. The higher low temperature toughness of TTS is related to the formation of intragranular acicular ferrite in the CGHAZ. When t8/5 ranged from 40 s to 100 s, the volume fraction of M-A islands in TTS can be reduced and the ferrite matrix microstructure can be refined by formation of fine intragranular acicular ferrite nucleated at Ti oxide inclusion, and the hardness in the simulated CGHAZ in TTS is lower than that of ATS at the same t8/5 value. Simultaneously, the austenite grain growth became abnormal and the second phase particles, TiN and Nb(C,N), were coarsened in ATS, resulting in bigger austenite grain size than that in TTS.

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    EFFECT OF HORIZONTAL MAGNETIC FIELD ON THE MICROSTRUCTURE OF DIRECTIONALLY SOLIDIFIED Ni-BASED SUPERALLOY
    DONG Jianwen REN Zhongming REN Weili LI Xi LI Xu
    Acta Metall Sin, 2010, 46 (1): 71-76. 
    Abstract   PDF (1512KB) ( 1318 )

    Some problems still exist in the directionally solidified superalloy, such as coarse dendritic structure, thick second phase and composition segregation. Many efforts have been made to enhance the overall performance of superalloy by improving the components and processes. However, the higher alloying degree not only increases the solidification segregation, but also increases the tendency of precipitating σ-phases, Laves-phases, μ-phases and other harmful phases. Therefore, it is crucial to improve the processes in order to enhance the performance of superalloy. It was known that the magnetic field effect is very obvious during the melt solidification process, which has been realized in the directional solidification of silicon, while the research on the magnetic field effect during the superalloy solidification process is few. So it is necessary to research the effect of magnetic field on directionally solidified superalloy. In this paper, the influence of horizontal magnetic field (≦0.8 T) on the microstructures of the superalloy DZ417G during directional solidification was investigated. It was found that the magnetic field can induce the appearance of freckle-like macrosegregation and the decrease of the primary dendrite arm spacing at a low growing speed, however, with the increase of the growth speed, the effects become weak. Based on the thermoelectric magnetic convection (TEMC) induced by the magnetic field during solidification and the effect of the convection on the microstructure, the above experimental results were discussed and analyzed.

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    MICROSTRUCTURE AND MICROSEGREGATION IN A Ni-BASED SINGLE CRYSTAL SUPERALLOY DIRECTIONALLY SOLIDIFIED UNDER HIGH THERMAL GRADIENT
    LIU Gang LIU Lin ZHAO Xinbao ZHANG Weiguo JIN Tao ZHANG Jun FU Hengzhi
    Acta Metall Sin, 2010, 46 (1): 77-83. 
    Abstract   PDF (1084KB) ( 1470 )

    In order to understand the effect of high thermal gradient on the microsegregation of refractory elements in Ni-based superalloys, a Ni-based single crystal superalloy containing 4% Re (mass fraction) was prepared by dual heating zone melting and liquid-metal cooling (LMC) directional solidification technique. Comparing with the traditional high rate solidification (HRS) method with thermal gradient G=20-40 K/cm, withdrawal rate V=50-100 $\mu$m/s and primary dendritic arm spacing λ1=200-400 μm, this technique can significantly increase the thermal gradient (up to 238 K/cm) and withdrawal rates (up to 500 $\mu$m/s). Planar-like and cellular-like solid-liquid interfaces, coarse dendrite and fine dendrite were sequentially obtained with increasing withdrawal rates. Under the condition of $G$=238 K/cm and $V$=500 $\mu$m/s, the primary dendritic arm spacing λ1 and the mean size of γ' precipitates (in dendrite core) obviously decreased to 61.3 and 0.04 μm, respectively. In addition, the microsegregation increased initially and then decreased with increasing withdrawal rate, especially for the microsegregations of W and Re. EPMA line scan indicated that solid-back diffusion has an obvious influence on the microsegregation for the fine dendrite structure under high thermal gradient directional solidification.

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    PHASE FIELD SIMULATION OF GROWTH KINETICS OF COHERENT Ni4Ti3 PRECIPITATE IN NiTi SHAPE MEMORY ALLOY
    KE Changbo MA Xiao ZHANG Xinping
    Acta Metall Sin, 2010, 46 (1): 84-90. 
    Abstract   PDF (1038KB) ( 2203 )

    The precipitation of metastable Ni4Ti3 particles and their distribution feature in Ni-rich NiTi shape memory alloys have significant influence on the subsequent martensitic transformation behavior and shape memory effect as well as superelasticity. The Ni4Ti3 particles with the space group R3 precipitate coherently along four {111} planes of the B2 matrix and form four pairs of conjugate variants. The diffusion-interface phase field model was used to simulate the nucleation and growth of the Ni4Ti3 precipitate in NiTi shape memory alloy, and its morphological evolution was characterized by solving Ginzburg-Landau equation for non-conserved field variables and Cahn-Hilliard diffusion equation for conserved field variables. More accurate crystallographic parameters and improved mathematical model were used in simulating the formations of 3D plate-shaped or 2D lenticular-shaped Ni4Ti3 variants. The time dependences of length, width and area fraction of Ni4Ti3 precipitate obey a power law, a linear and a logarithmic equation, respectively. The length-to-width ratio of the precipitate is not a constant value, but increases rapidly in the early stage of precipitation and slows down in later stage, which is corresponding to the plate- or lenticular-shaped morphologies and coincident with the experimental observations reported.

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    VISCOELASTIC-PLASTIC ANALYSIS OF BROADENING OF SLAB IN THE SECONDARY COOLING ZONE OF CONTINUOUS CASTING
    FU Jianxun LI Jingshe ZHANG Hui
    Acta Metall Sin, 2010, 46 (1): 91-96. 
    Abstract   PDF (992KB) ( 1196 )

    The 3D viscoelastic-plastic thermal-mechanically coupled finite element model was established by a commercial software MSC.Marc on the basis of secondary development, and used to simulate the situation of slab's broadening in the secondary cooling zone. The results showed that the slab's broadening mainly emerged in the former segments of the secondary cooling zone, and the broadening rate has a gradually increasing trend from the first segment to the sixth segment. The broadening of slab has a close relationship with bulging along the thickness direction. The results simulated by using viscoelastic-plastic model revealed that the law of the slab's broadening is excellent agreement with the actual deformation. The broadening of slab is the result of viscoelastic-plastic deformation of the slab shell under the pressure of core of molten steel.

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    FIRST-PRINCIPLES CALCULATIONS OF STRUCTURAL STABILITIES AND ELASTIC PROPERTIES OF AB2 TYPE INTERMETALLICS IN ZA62 MAGNESIUM ALLOY
    ZHOU Dianwu XU Shaohua ZHANG Fuquan PENG Ping LIU Jinshui
    Acta Metall Sin, 2010, 46 (1): 97-103. 
    Abstract   PDF (982KB) ( 1754 )

    Structural stabilities, elastic properties and electronic structures of Mg2Sn, MgZn2 and MgCu2 in ZA62 magnesium alloy have been determined from first-principles calculations by using Castep and Dmol program based on the density functional theory. The calculated heats of formation and cohesive energies showed that Mg2 Sn has the strongest alloying ability and MgCu2 the highest structural stability. The calculated bulk moduli (B), anisotropy values (A), Young's moduli (E), shear moduli (G) and Poisson ratio (ν) showed that MgZn2 and MgCu2 both are ductile, on the contrary, Mg2 Sn is brittle, and among the three phases MgZn2 is a phase with the best plasticity. Their tested melting temperatures are within the ranges calculated from elastic constants (±300 K) and bulk moduli (±500 K), the estimated values from elastic constant have the smallest average relative error, the calculated melting temperature of Mg2Sn phase is in well agreement with the experimental one and the error relative to the experiment result is about 0.31%. MgCu2 has higher melting temperature, i.e. better structural stability among the three compounds. The calculations of thermodynamic properties show that the Gibbs free energy of MgCu2 is also the smallest within 298-573 K range, indicating the structural stability of MgCu2  does not change with the elevated temperature. The calculations of the density of states (DOS) and Mulliken electronic populations showed that the reason of MgCu2 having highest structural stability in ZA62 magnesium alloy attributes to MgCu2 phase having more ionic bonds below Fermi level compared with those of Mg2 Sn and MgZn2 phases.

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    MULTI-OBJECTIVE OPTIMUM DESIGN FOR STRENGTH AND HEAT INSULATION OF METAL FOAM WITH DUAL-SIZE CELLULAR STRUCTURE
    KOU Dongpeng YU Jilin
    Acta Metall Sin, 2010, 46 (1): 104-110. 
    Abstract   PDF (1221KB) ( 947 )

    Finite element simulations are performed to study the steady state heat conduction of dual--size metal foams. Simulation results reveal that for a given density, the thermal conductivity of dual-size foams is higher than that of uniform cell size foam. However, the effective thermal conductivity decreases while increasing the cell radius ratio r/R in dual-size foams. A multi-objective optimum design model considering structure strength, heat insulation and light mass requirement is developed, where the objective function is obtained through polynomial fitting of the numerical results. The model is solved by the constraint method< and the optimum cell radius ratio, density and thickness of metal foam are obtained for dual-size metal foams. A comparison of the heat insulation capacity of the dual-size metal foam to the single-size metal foam having the same mass and yield strength shows that the heat insulation capacity of the former is much higher than that of the latter. Hence the dual-size foam structure is superior to that of the uniform cell foam when both load--bearing and heat insulation capacities are required.

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    NUMERICAL SIMULATIONS OF SHOT-PEENING PROCESS AND IMPACT EFFECT
    ZHANG Hongwei ZHANG Yidu WU Qiong
    Acta Metall Sin, 2010, 46 (1): 111-117. 
    Abstract   PDF (1352KB) ( 1269 )

    The shot--peening process and impact effect were simulated by using software LS--DYNA. Propagation and interaction of stress waves in the treated material were analyzed based on numerical simulation results. The stress wave structure, high strain-rate effect and attenuation of stress wave were also investigated. The overlapping ratio between shots was studied and the high peening coverage model was established. The effects of impact sequence, material strain--rate and initial residual stress on the residual stress and the surface deformation were examined. The results indicate that the high strain-rate induced by shot impact is related to the elastic and plastic wave structure. The surface quality is essentially affected by overlapping ratio and its approximate critical value is found to be 1/2. The effect of impact sequence can be neglected, but the strain rate plays an important role in determining the level and distribution of the residual stress field. The influence of original residual stress in the target is significantly dependent on the impact velocity. The shallow pocket in depth is induced on the top surface of material by multiple impacts, and the surface deformation increases with the increase of impact time.

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    THE SINGLE EFFECT OF MICROBE ON THE CORROSION BEHAVIORS OF 45 STEEL IN SEAWATER OF TROPICAL OCEAN ENVIRONMENT
    WU Jinyi XIAO Weilong CHAI Ke YANG Yuhui
    Acta Metall Sin, 2010, 46 (1): 118-122. 
    Abstract   PDF (869KB) ( 1438 )

    Biological elements have significant impact on lifetime prediction of marine carbon steel facilities. Microbe can produce pitting, crevice corrosion, selective dealloying and stress-oriented hydrogen-induce cracking, which accelerates both localized and average corrosion rates of carbon steel. The formation of microbe films can also reduce the steel corrosion rate through inhibition of oxygen diffusion and depletion of oxygen in the electrolyte and metal/solution interface. A comparing study of the corrosion behaviors of 45 steel in natural seawater and in sterile seawater in tropic condition shows that in most of immerging periods, the bacterial activity at the interface accelerates the average corrosion rate of the steel. However, when the corrosion time is 28 d, the biofilms inhibit the corrosion of 45 steel. The species and contents of microbe significantly influence the corrosion behavior of the steel. The microbe in the corrosion product mainly consists of Pseudomonas, Vibrio, Crenothrixandleptothrix, Thiobacillus, and Sulfate-reducing bacteria. The content of aerobe does not change with increasing the immerging time, but the content of anaerobe increases with increasing immerging time. The regular change of the content of microbe with the immerging time leads to the different microbe corrosion mechanisms for 45 steel.

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    CATHODIC ELECTROCHEMICAL BEHAVIORS OF MILD STEEL IN SEAWATER
    ZOU Yan ZHENG Yingying WANG Yanhua WANG Jia
    Acta Metall Sin, 2010, 46 (1): 123-128. 
    Abstract   PDF (1164KB) ( 1277 )

    The cathodic electrochemical behavior of A3 mild steel in seawater was studied and the roles of the formed rust layers in cathodic process were analyzed by means of electrochemical tests and XRD. The results showed that the rust formed could be classified into outer layer and inner layer.  The inner layer is mainly composed of γ-FeOOH, α-FeOOH, β-FeOOH and Fe3O4/γ-Fe2O3, while the main phases in the outer layer changed with the increase of immersion time.  During the initial immersion period of 126 d, the phase is γ-FeOOH, but after about 364 d immersion, the phases are γ-FeOOH, α-FeOOH and Fe3O4/γ-Fe2O3.  These rust layers play different roles in the cathodic process.  Both the outer and inner rust layers can prevent the dissolved oxygen from diffusing into the steel substrate, while the inner layer could also participate in reduction reaction which accelerated the cathodic reaction.  A parameter α was induced to evaluate the participation degree of rust in the reduction reaction.  The value of parameter $\alpha$ obviously increased during the first 7 d immersion, and almost didn't change after 168 d immersion.  Changes of components in outer and inner layers were discussed and the interactions of different components were analyzed.

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