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ISSN 1005-0302
CN 21-1315/TG
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      28 March 2007, Volume 23 Issue 02 Previous Issue    Next Issue
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    Research Articles
    TEM investigations on layered ternary ceramics
    Zhijun LIN, Meishuan LI, Yanchun ZHOU
    J. Mater. Sci. Technol., 2007, 23 (02): 145-165. 
    Abstract   HTML   PDF (8728KB)

    Layered ternary ceramics represent a new class of solids that combine the merits of both metals and ceramics. These unique properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), convergent beam electron diffraction (CBED) represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Microstructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the ``Processing-Structure-Property" relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.

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    Bi-based Nanowire and Nanojunction Arrays: Fabrication and Physical Properties
    Liang LI, Guanghai LI, Xiaosheng FANG
    J. Mater. Sci. Technol., 2007, 23 (02): 166-181. 
    Abstract   HTML   PDF (6667KB)

    This article reviews the recent developments in the fabrication and properties of one-dimensional (1D) Bi-based nanostructures, including Bi, Sb, BixSb1-x and Bi2Te3 nanowire arrays, and Bi-Bi and Bi-Sb nanojunction arrays. In this article, we present an effective method to fabricate Bi nanowire arrays with different diameters in anodic alumina membrane (AAM) with a single pore size by the pulsed electrodeposition. The fabrication of the high-filling and ordered Bi1-xSbx and Bi2Te3 single crystalline nanowire arrays, the Bi nanowire metal-semiconductor homojunction and Bi-Sb nanowire metal-semiconductor heterojunction arrays by the pulsed electrodeposition are reported. The factors controlling the composition, diameter, growth rate and orientation of the nanowires are analyzed, and the growth mechanism of the nanowire and nanojunction arrays are discussed together with the study of the electrical and thermal properties of Bi-based nanowires and nanojunctions. Finally, this review is concluded with some perspectives on the research directions and focuses in the Bi-based nanomaterials fields.

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    Preparation and Characterization of Fe3O4 Magnetic Nano-particles by 60Co γ-ray Irradiation
    Mingcheng YANG, Hongyan SONG, Chengshen ZHU, Suqin HE, Ya GAO
    J. Mater. Sci. Technol., 2007, 23 (02): 182-184. 
    Abstract   HTML   PDF (391KB)
    By using a new method, 60Co γ-ray irradiation, Fe3O4 magnetic nano-particles were successfully synthesized at room temperature under ambient pressure. The structure, morphology and magnetic properties of these nano-particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM), respectively. The radiation formation mechanism was also discussed. The results show that the absorbed dose can greatly influence the structure, morphology and magnetic properties of the products. XRD and TEM studies show that the product prepared by γ-ray irradiation (10 kGy) is pure Fe3O4 phase and the mean diameter of these nano-particles is about 21 nm. The Fe3O4 nano-particles synthesized by γ-ray irradiation (10 kGy) are mainly in small cubic shape and the size uniformity of these particles is good.
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    Two Alternative Routes to MS2 Nanotubes
    Yanqing LIU, Changsheng LI, Jinghai YANG, Zhong HUA, Junmao LI, Kehong AN, Shuhuo Zhao
    J. Mater. Sci. Technol., 2007, 23 (02): 185-188. 
    Abstract   HTML   PDF (1308KB)
    Inorganic tubular nanostructure MS2 (M=Mo, W, Nb, Ta) were synthesized by two alternative routes. Thermal decomposition method was used for producing fullerence-like MS2 (M=Mo, W) nanotubes on Al2O3 template using ammonium sulfur respectively; NbS2, and TaS2 nanotubes were obtained successfully by reducing corresponding metal trisulfide in a stream of H2 (mixed with N2 in some cases) at elevated temperatures. Detailed experimental procedure, and the characterization of associated results, were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The result reveals that products are composed of high density of MS2 tubular nanostructures with the diameter of 100 nm and length of tens of micrometers. And no mistake, these 1-D (one-dimensional) tubular nanomaterials added quantities and varieties in the growing family of nanotubes of inorganic layered materials.
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    A Comparative Study on the Selected Area Electron Diffraction Pattern of Fe Oxide/Au Core-shell Structured Nanoparticles
    Qianghua LU, Kailun YAO, Dong XI, Zuli LIU, Xiaoping LUO, Qin NING
    J. Mater. Sci. Technol., 2007, 23 (02): 189-192. 
    Abstract   HTML   PDF (1109KB)

    The selected area electron diffraction (SAED) pattern of magnetic iron oxide core/gold shell nanoparticles has been studied. For the composite particles with mean size less than 10 nm, their SAED pattern is found to be different from either the pattern of pure Fe oxide nanoparticles or that of pure Au particles. Based on the fact that the ring diameters of these composite particles fit the characteristic relation for the fcc structure, the Au atoms on surfaces of the concerned particles are supposed to pack in a way more tightly than they usually do in pure Au nanoparticles. The driving force for this is the coherency strain which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core.

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    Pressure-Induced Structural Transitions of the Zinc Sulfide Nano-particles with Different Sizes
    Yuewu PAN, Jie YU, Zhan HU, Hongdong LI, Qiliang CUI, Guangtian ZOU
    J. Mater. Sci. Technol., 2007, 23 (02): 193-195. 
    Abstract   HTML   PDF (783KB)
    ZnS nano-particles with average sizes of 10 nm and 5 nm were fabricated by sol-gel method, and their pressure-induced phase transformations were in-situ examined in a diamond anvil cell by energy dispersive X-ray diffraction (EDXD) from ambient pressure to 35.0 GPa. From the obtained interplanar spacing data, the volume compression ratios were derived at different pressures, and then the bulk modulus and its pressure derivative were obtained by fitting to the Murnaghan equation. It is found that both ZnS nano-particles initially in the zinc-blende phase transformed to cubic NaCl structure in the presence of pressure and the transition was reversible when the pressure was released. Moreover, it is suggested that a smaller particle size will induce a larger transition pressure.
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    New Bi-metallic Single Source Precursors for the Deposition of Thin Films of Semiconductor Ceramics
    U.Salma, M.Mazhar, J.I.Akhter, Z.Ali
    J. Mater. Sci. Technol., 2007, 23 (02): 196-200. 
    Abstract   HTML   PDF (1501KB)
    Stable binary single source precursors (SSP) for the deposition of thin films of ceramic semiconductors of composition SnO•GeO were synthesized by close circuit chemical vapour deposition (CCCVD) method. Elemental analysis and spectroscopic techniques were used to characterize the precursors. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. Resistivity measurements were conducted to show that the films are of semiconducting nature.
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    Microstructure and Wear Behaviour of Laser-induced Thermite Reaction Al2O3 Ceramic Coating on AA7075 Aluminum Alloy
    Kaijin HUANG, Xin LIN, Changsheng XIE, T.M.Yue
    J. Mater. Sci. Technol., 2007, 23 (02): 201-206. 
    Abstract   HTML   PDF (1240KB)
    The microstructure and wear behaviour of the thermite reaction coating produced by the hybrid laser cladding-remelting on AA7075 aluminum alloy for the systems of Al-CuO-SiO2, Al-Cr2O3-SiO2, Al-Fe2O3-SiO2, and Al-TiO2-SiO2 were studied. The results of the X-ray diffraction (XRD) analysis show that in all the four reaction coatings, α-Al2O3 and γ-Al2O3 phases were present at the top surface, together with various intermetallic phases, the corresponding reduced metal and Al phase in the fusion zone. Under the dry sliding condition, the wear resistance, in terms of weight loss, of the laser-clad specimens was considerably higher than that of the untreated specimen. The predominant wear mechanism of the former specimens was abrasive wear, while for the latter, it was the adhesive wear that prevailed.
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    Compressive Creep Behavior of TiC/AZ91D Magnesium-matrix Composites with Interpenetrating Networks
    Liqing CHEN, Jinhua GUO, Baohai YU, Zongyi MA
    J. Mater. Sci. Technol., 2007, 23 (02): 207-212. 
    Abstract   HTML   PDF (976KB)
    The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose, the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponent of AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 kJ/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.
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    The Role of Particles in Fatigue Crack Propagation of Aluminum Matrix Composites and Casting Aluminum Alloys
    Zhenzhong CHEN, Ping HE, Liqing CHEN
    J. Mater. Sci. Technol., 2007, 23 (02): 213-216. 
    Abstract   HTML   PDF (562KB)
    Fatigue crack propagation (FCP) behaviors were studied to understand the role of SiC particles in 10 wt pct SiCp/A2024 composites and Si particles in casting aluminum alloy A356. The results show that a few particles appeared on the fracture surfaces in SiCp/Al composites even at high △K region, which indicates that cracks propagated predominantly within the matrix avoiding SiC particles due to the high strength of the particles and the strong particle/matrix interface. In casting aluminum alloy, Si particle debonding was more prominent. Compared with SiCp/Al composite, the casting aluminum alloy exhibited lower FCP rates, but had a slight steeper slope in the Paris region. Crack deflection and branching were found to be more remarkable in the casting aluminum alloy than that in the SiCp/Al composites, which may be contributed to higher FCP resistance in casting aluminum alloy.
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    Butt-welding Residual Stress of Heat Treatable Aluminum Alloys
    C.M.Cheng
    J. Mater. Sci. Technol., 2007, 23 (02): 217-222. 
    Abstract   HTML   PDF (1236KB)
    This study, taking three types of aluminum alloys 2024-T351, 6061-T6 and 7075-T6 as experimental materials, conducted single V-groove GTAW (gas tungsten arc welding) butt-welding to analyze and compare the magnitude and differences of residual stress in the three aluminum alloys at different single V-groove angles and in restrained or unrestrained conditions. The results show that the larger the grooving angle of butt joint, the higher the residual tensile stress. Too small grooving angle will lead to dramatic differences due to the amount of welding bead filler metal and pre-set joint geometry. Therefore, only an appropriate grooving angle can reduce residual stress. While welding, weldment in restrained condition will lead to a larger residual stress. Also, a residual stress will arise from the restraint position. The ultimate residual stress of weldment is determined by material yield strength at equilibrium temperature. The higher the yield strength at equilibrium temperature, the higher the material residual stress. Because of its larger thermal conductivity, aluminum alloy test specimens have small temperature differential. Therefore, the residual tensile stress of all materials is lower than their yield strength.
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    Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy
    T.Senthil Kuma, V.Balasubramanian, M.Y.Sanavullah, S.Babu
    J. Mater. Sci. Technol., 2007, 23 (02): 223-229. 
    Abstract   HTML   PDF (5939KB)
    Medium strength aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG (tungsten inert gas) welding due to its comparatively easier applicability and better economy. In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy. Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.
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    High Velocity Forming of Aluminum Cylindrical Cups-Experiments and Numerical Simulations
    Mustafa YASAR, Ibrahim KADI
    J. Mater. Sci. Technol., 2007, 23 (02): 230-236. 
    Abstract   HTML   PDF (5241KB)
    A new two stage detonation forming machine was developed and cylindrical aluminum cups were formed by using gas detonation forming technology. The forming process was analyzed with the explicit finite element method with various parameters and ANSYS/LS-DYNA software. Defects of wrinkling and rupture were predicted for some forming conditions. The strain and the thickness distribution results were in good agreement with the experimental results. It was seen that thinning and forming mainly take place during the one fourth of the time. The effects of detonation pressure and blank holding force on the deformation of the work pieces were discussed. The numerical results were compared with those obtained in the experiments.
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    Deformation Localization and Shear Fracture of a Rapidly Solidified Al-Fe-V-Si Alloy at Elevated emperature
    Yongbo XU
    J. Mater. Sci. Technol., 2007, 23 (02): 237-241. 
    Abstract   HTML   PDF (1585KB)
    The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.
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    History-dependent Selection of Primary Dendritic Spacing in Directionally Solidified Alloy
    Linlin WANG, Xin LIN, Guolu DING, Lilin WANG, Weidong HUANG
    J. Mater. Sci. Technol., 2007, 23 (02): 242-246. 
    Abstract   HTML   PDF (436KB)
    Directional solidification experiments were carried out for succinonitrile-1.0 wt pct acetone alloy with the orientation of dendritic arrays being not parallel to the direction of the temperature gradient. Experimental results show that there exists an allowable range of primary dendritic spacing under a given growth condition. The average primary spacing depends not only on the current growth conditions but also on the way by which the conditions were achieved. The upper limit of the allowable range becomes smaller in comparison with that with <001> direction of dendrite arrays parallel to the direction of the temperature gradient, which means that the history-dependence of dendritic growth is weaker under this condition. The lower limit obtained is compared with a self-consistent model, which shows a good agreement with experimental results.
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    Effect of Holding Time on Thixotropic Fluidity of Semi-solid AZ91D Magnesium Alloy
    Zesheng JI, Maoliang HU, Xiaoping ZHENG
    J. Mater. Sci. Technol., 2007, 23 (02): 247-252. 
    Abstract   HTML   PDF (1160KB)
    To investigate the thixotropic fluidities, microstructures and mechanical properties of semi-solid AZ91D magnesium alloy during reheating, a self-made die set with channels of different sizes were used. The results show that critical forming forces and maximal forming forces could be obtained and related to the holding times in the semi-solid forming process. In the holding time of 0-2700 s, with increasing the holding time, maximal forming force decreased sharply and critical forming force decreased slowly. In the whole thixotropic flowing process, the filling-in was steady and the surface fineness was good. The forming force increased when the slurry changed the flowing direction or flowed from the big-diameter chamber to the small-diameter one. The tensile strength and elongation to failure of the sample after holding time for 2700 s, compared to as-cast sample, are increased by approximately 42.7% and 180%, respectively, and the fractured surfaces presented dimple-like pattern.
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    Microstructural and Microhardness Variation of Amorphous Fe78Si9B13 Alloy during Bend Stress Relaxation
    Xifeng LI, Kaifeng ZHANG, Changli WANG, Wenbo HAN, Guofeng WANG
    J. Mater. Sci. Technol., 2007, 23 (02): 253-256. 
    Abstract   HTML   PDF (1486KB)
    The amorphous Fe78Si9B13 ribbons were bend stress relaxed at various temperature well below the crystallization temperature (Tx) for different time. The effect of pre-annealing on the subsequent bend stress relaxation was examined. The variation of the microstructure and microhardness during bend stress relaxation process was studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and Vickers microhardness test, respectively. Curvature radius of the amorphous Fe78Si9B13 ribbons decreased with increase bend stress relaxation temperature and time. The microhardness of the stress relaxed specimens increased with time at 300℃ due to the forming of nanocrystals during bend stress relaxation. The pre-annealing reduced the decrease rate of the curvature radius of stress relaxed specimens.
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    Effect of Si3N4 Addition on the Mechanical Properties, Microstruc-tures, and Wear Resistance of Ti-6Al-4V Alloy
    Ruihua HU, Montasser M.Dewidar, Hyo-Jin KIM, Jae-Kyoo LIM
    J. Mater. Sci. Technol., 2007, 23 (02): 257-261. 
    Abstract   HTML   PDF (801KB)
    In order to improve the wear resistance of Ti-6Al-4V, different amounts of Si3N4 powder were added into the alloy powder and sintered at 1250℃. Porous titanium alloy with higher wear resistance was successfully fabricated. At sintering temperature, reaction took place and a new hard phase of Ti5Si3 formed. The mechanical properties of the fabricated alloys with different amounts of Si3N4 addition were investigated. The hardness of Ti-6Al-4V, which is the index of wear resistance, was increased by the addition of Si3N4. Amounts of Si3N4 addition have very significant influences on hardness and compressive strength. In present study, titanium alloy with 5 wt pct Si3N4 addition has 62% microhardness and 45% overall bulk hardness increase, respectively. In contrast, it has a 16.4% strength reduction. Wear resistance was evaluated by the weight loss during wear test. A new phase of Ti5Si3 was detected by electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) method. The original Si3N4 decomposed during sintering and transformed into titanium silicide. Porous structure was achieved due to the sintering reaction.
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    EBSD Investigation on Oriented Nucleation in IF Steels
    Shengquan CAO, Youyuan LI, Jinxu ZHANG, Jiansheng WU
    J. Mater. Sci. Technol., 2007, 23 (02): 262-266. 
    Abstract   HTML   PDF (2150KB)
    The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free (IF) steel sheets was investigated using electron back-scatter diffraction (EBSD). In addition, the origin of nuclei with specific orientations was studied. The formation of recrystallization texture was explained by oriented nucleation. Most nuclei have a high misorientation angle of 25-55℃ with the surrounding deformed matrices, but no specific orientation of misorientation axis between the nucleus and the surrounding deformed matrix is observed. The stored energy of deformed grains is in the decreasing order of the {111}<112>, {111}<110>, {112}<110> and {001}<110> orientations. New {111}<110> grains are nucleated within deformed {111}<112> grains and new {111}<112> grains originate in the deformed {111}<110> grains.
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    Thermodynamic Research on Precipitates in Low Carbon Nb-Microalloyed Steels Produced by Compact Strip Production
    Song XIANG, Guoquan LIU, Yang LI, Changrong LI, ong WANG
    J. Mater. Sci. Technol., 2007, 23 (02): 267-272. 
    Abstract   HTML   PDF (13197KB)
    Microalloying element Nb in low carbon steels produced by compact strip production (CSP) process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement. With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice, a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that (NbTi) (CN) precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.
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    A New Method for Improving Strength and Plasticity of Steel Wire
    Fei DING, Guoyi TANG, Zhuohui XU, Shaoquan TIAN
    J. Mater. Sci. Technol., 2007, 23 (02): 273-276. 
    Abstract   HTML   PDF (851KB)

    Specially designed wire-drawing equipment with multiple electropulse generator was introduced. The influences of multiple electropulses processing on the microstructure and properties of the hardened steel wire were investigated. Samples treated by direct current under the same current density as that in multiple electropulses processing were carried out for contrast analysis. The results show that the optimized parameters of multiple electropulses processing will be facilitated to increase the nucleation rate and slow down the growth rate of recrystallized grains. Consequently, massive superfine grains of micro and sub-micro scale could be found in the steel wire. Thereby, the elongation was significantly enhanced with a relatively small strength reduction in comparison with as-received cold-drawing steel wires. Outstanding mechanical properties of steel wire were obtained.

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    Element Analysis of Instrumented Sharp Indentations into Pressure-sensitive Materials
    Minh-Quy LE, Seock-Sam KIM
    J. Mater. Sci. Technol., 2007, 23 (02): 277-282. 
    Abstract   HTML   PDF (2995KB)

    Finite element analysis was carried out to investigate the conical indentation response of elastic-plastic solids within the framework of the hydrostatic pressure dependence and the power law strain hardening. A large number of 40 different combinations of elasto-plastic properties with n ranging from 0 to 0.5 and σy/E ranging from 0.0014 to 0.03 were used in the computations. The loading curvature C and the average contact pressure pave were considered within the concept of representative strains and the dimensional analysis. Dimensionless functions associated with these two parameters were formulated for each studied value of the pressure sensitivity. The results for pressure sensitive materials lie between those for Von Mises materials and the elastic model.

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    Key Problems in Microforming Processes of Microparts
    Chunju WANG, Debin SHAN, Bin GUO, Jian ZHOU, Lining SUN
    J. Mater. Sci. Technol., 2007, 23 (02): 283-288. 
    Abstract   HTML   PDF (1291KB)

    From the viewpoint of production engineering, microforming is considered as an effective process to fabricate various microparts. Several key problems in microforming processes were investigated. A new microforming apparatus with a high stiffness piezoelectric actuator as the punch driver was developed to produce microparts. To improve the forming abilities and locate the billets, a floating microdie was designed. The size effects of the billets and die cavities on the microforming abilities were studied with upsetting and coining tests, respectively. And the isothermal microforming process of microgears was performed with the developed microforming apparatus. Several analysis methods were used to evaluate the forming quality of the microparts.

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