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

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    , Volume 42 Issue 11 Previous Issue    Next Issue
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    Research Articles
    Texture and Anisotropy of Jc of ex situ MgB2/Fe Mono—Filamentary Tapes
    SUO Hongli; MA Hongxia; WANG Ying; LIU Min; ZHAO Yue; MA Lin; ZHOU Meiling
    Acta Metall Sin, 2006, 42 (11): 1121-1124 . 
    Abstract   PDF (650KB) ( 896 )
    In this paper, the critical current density of ex-situ MgB2/Fe sheathed mono- filamentary tapes has been measured at various magnetic fields and different temperatures. The texture and anisotropy of Jc in these tapes were presented in detail. The commercial MgB2 powder was ball-milled in order to obtain different starting powder grain sizes. It was found that the anisotropy of Jc is influenced significantly by the starting powder grain size. The crystallite size of the annealed MgB2 core is more pronounced for the sample with larger starting powder grain size . In order to understand the origin of Jc anisotropy, we have undertaken detailed X-ray refinements on the degree of texturing in the MgB2 filaments after mechanical removal of the Fe sheath. The degree of texturing of the filaments at the interface Fe/MgB2 and in the centre of the MgB2 filaments has been determined. A moderate texture has been found, being slightly better at the interface between Fe and MgB2 core. The correlation among the starting power size, texturing and the anisotropy of Jc was discussed.
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    Analysis of Valence Electronic Structures and Properties of MoSi2 And WSi2
    PENG Ke; YI Maozhong; RAN Liping
    Acta Metall Sin, 2006, 42 (11): 1125-1129 . 
    Abstract   PDF (695KB) ( 957 )
    According to the empirical electron theory of solids and molecules, the valence electron structure of MoSi2 and WSi2 were quantitatively studied, and the values of valence electrons on every bond in MoSi2 and WSi2 crystals were calculated by the method of bond length difference. The results showed that the strongest bonds in the unit cells of MoSi2 and WSi2 were Mo-Si and W-Si bond along <331> direction separately, whose valence electron numbers and the bond energy have great impact on the hardness and melting point of MoSi2 and WSi2 phases, respectively. Since the numbers of lattice electrons in a crystal influence its conductivity and plasticity, and there were lattice electrons with higher densities in MoSi2, the conductivity and plasticity of MoSi2 were better than WSi2. Also, it is infered that the brittleness of MoSi2 and WSi2 could be explained primarily by a heterogeneity of bond distribution.
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    Combined Treatment of Sr and B and Evaluation of Refinment--Modification
    CHEN Xiang; GENG Huiyuan; LI Yanxiang
    Acta Metall Sin, 2006, 42 (11): 1130-1136 . 
    Abstract   PDF (1228KB) ( 712 )
    The effects of boron and strontium on the solidified structures of hypoeutectic Al-Si alloys by combination addition of boron and strontium have been studied by quantitative metallography and chemical analysis. The results show that the presence of strontium has no remarkable effects on the efficiency of grain refinement of Al-7Si alloys. But the presence of boron reduces the effective strontium level in the melt Al-7Si alloys and thus decreases the modification level of Al-7Si alloys. Based on these, the relationship between the shape of solidification segment of the cooling curve and the features of melt hypoeutectic Al-Si alloys has been studied by computer-aided cooling curve analysis and pattern cooling curve recognition approaches. It is indicated that both the grain size difference and the modification level difference converge to zero when the comprehensive parameter Ω, which expresses the difference between cooling curves, approaches to zero. The shape of the solidification segment of a cooling curve can token the features of the Al-7Si alloy melt by combination addition of boron and strontium. Based on a database established from a large amount of experimental results, the on-line prediction of eutectic modification level of Al-7Si alloy melt has been realized.
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    An Analysis of Thermal Elastoplastic Behavior of Continuous Casting Slab Mold
    LIU Xudong; ZHU Miaoyong; CHENG Nailiang
    Acta Metall Sin, 2006, 42 (11): 1137-1142 . 
    Abstract   PDF (742KB) ( 717 )
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    Water Model Study on Removing Inclusions in a Ladle With Argon Injected Through
    ZHENG Shuguo; ZHU Miaoyong
    Acta Metall Sin, 2006, 42 (11): 1143-1148 . 
    Abstract   PDF (785KB) ( 1157 )
    The removal efficiency of non-metallic inclusions from molten steel in gas-stirred ladles will directly affect the quality of steel product. In the present work, the effects of time and gas flowrate on inclusion removal in a ladle with eccentric bottom gas injected through nozzle and porous plug were investigated by choosing emulsion drops simulated as inclusions in a water model. The results show that most of the inclusions can be removed in eight minutes with smaller flowrates, while sixteen minutes needed with larger flowrates. All the inclusions which have the possibility to be removed almost disappeared from the system in twenty-eight minutes. With gas blowing through nozzle, there was a gas flowrate for the best of inclusions removal. With gas injected through porous plug, smaller gas flowrates seemed to be more efficient for inclusions removal. And within a range of gas flowrates, gas injected through porous plug seemed to be more efficient for inclusions removal than gas blowing through nozzle.
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    Molecular Dynamic Simulations of the Stick--Slip Phenomenon on the Surface of Cu Single CrystaL
    CHENG Dong; YAN Zhijun; YAN Li
    Acta Metall Sin, 2006, 42 (11): 1149-1152 . 
    Abstract   PDF (672KB) ( 1010 )
    The mechanisms of micro stick-slip phenomenon were investigated with the 3D Molecular Dynamics Simulations (MDS) of single-asperity dry friction on homogeneous Cu. At the atomic scale, the regular arrangement of atoms on the sliding surfaces makes a large and a small “sawtooth” displayed in the friction force curve. This can be explained by the appearance and disappearance of the dislocations on the sliding surfaces. The magnitudes of “sawtooth” depend on the load, sliding speed, and the lattice difference across the sliding surface. The higher the load, the more atoms to be moved during dry friction, and the less the magnitude of the small “sawtooth”. The magnitude of the small “sawtooth” is linear to the sliding speed. The stick-slip phenomenon varies at different sliding surfaces and different sliding directions, but the period of the “sawtooth” is just the lattice constant of the substrate along the sliding direction.
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    Investigation on the Micro-Deformation Characteristics of Porous NiTi Shape Memory Alloy Using Sem Moire Method
    JIANG Haichang; DU Hua; XIE Huimin; RONG Lijian
    Acta Metall Sin, 2006, 42 (11): 1153-1157 . 
    Abstract   PDF (864KB) ( 850 )
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    Molecular Dynamics Simulation of Au Nano--Scale Particle Deposited on Au Surface During Cold Spraying
    GAO Hong; ZHAO Liangju; ZENG Danling; GAO Lijuan
    Acta Metall Sin, 2006, 42 (11): 1158-1164 . 
    Abstract   PDF (783KB) ( 868 )
    Cold spray is a rapidly emerging coating technology, in which spray particles in a solid state are deposited via plastic impact on a substrate to form a coat. In cold spray, spray particles are accelerated to a very high velocity by supersonic gas and the temperature of spray particles is much lower than the melting point. Molecular dynamics simulation was applied to the investigation of the deposition process of Au152, Au276, and Au420 clusters on Au surface. Interaction potential with glue model was used in the simulation. The impact, deposition process and the final appearances of cluster and substrate were observed directly by taking ‘snapshot’. It was found that the melt phenomenon occurred in the local area during the impact and deposition by studying the temperature of substrate. In addition, the influence factors on deposition, incident velocity of cluster and the size of cluster, were discussed in this paper simply.
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    Evaluation of Porosity in Lotus--Type Porous Cu Fabricated with Gasar Process
    ZHANG Huawei; LI Yanxiang; LIU Yuan
    Acta Metall Sin, 2006, 42 (11): 1165-1170 . 
    Abstract   PDF (842KB) ( 1155 )
    Lotus-type porous copper with elongated pores has been fabricated by a unidirectional solidification method under a pressurized hydrogen or gas mixture of hydrogen and argon. Through solving the steady-state solute distribution function before the solidification front, the hydrogen content in the solid metal was calculated and a new theoretical model for calculating porosity was founded. Solidification velocity and the diffusivity of hydrogen were taken into account and the predicted porosity values are in good agreement with the experimental results under different partial pressures of hydrogen and argon. In addition, the relationship between porosity and partial pressures of mixed gases was obtained.
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    Gas Pressure Condition for Obtaining Uniform Lotus--Type Porous Structure by Gasar Process
    ZHANG Huawei; LI Yanxiang; LIU Yuan
    Acta Metall Sin, 2006, 42 (11): 1171-1176 . 
    Abstract   PDF (889KB) ( 878 )
    Gas pressure is the effective and most easily controlled parameter for fabricating lotus-type porous metals with long cylindrical regular ordered pores by unidirectional solidification of metal-gas eutectic. The kind of gas which is applicable for Gasar process was discussed in this article. Gas pressure condition for obtaining uniform lotus-type porous structure in which the spatial distribution and the size of pores both are highly uniform has been established through analyzing the influence of gas pressure on the position of eutectic point and solidification mode (eutectic, hypereutectic and hypoeutectic mode), and comparing the homogeneity of lotus-type porous structures obtained under three solidification mode. As an example, the experimental results of magnesium and hydrogen system verified the above theory.
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    Microstructures of Ti50-0.5xNi50-0.5xCux Alloys
    WANG Jian; JIN Wei; CAO Mingzhou; YANG Rui
    Acta Metall Sin, 2006, 42 (11): 1177-1181 . 
    Abstract   PDF (790KB) ( 702 )
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    Thermodynamics Properties of Ternary Bath of Coloring Hot--Dip Galvanization
    LE Qichi; CUI Jianzhong
    Acta Metall Sin, 2006, 42 (11): 1182-1186 . 
    Abstract   PDF (661KB) ( 899 )
    The activities and activity interaction parameters of two kinds of ternary alloy baths, Zn-Mn-Me and Zn-Ti-Me, were calculated by use of Shuanglin Chen model and Zhongting Ma expression. The results indicate that the activity of color generation element Mn or Ti increased as addition of Ni or Cu, where the effect of Ni is superior to Cu, however, the addition of Ti decreased the activity of Mn in Zn-Mn bath, and the opposite behavior for Mn in Zn-Ti. There is an inevitable relationship between the activity of components and color generation effectiveness. That is to say, the additives which can increase the activities of color generation elements would be in favor of improving the combination properties of hot-dip bath, and finally of color generation effectiveness. Therefore, Mn, Ni, and Cu are favorable elements for coloring hot-dip bath, and the advantages and disadvantages of Ti are related with its concentration, which is consistent with the results of technology experiments.
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    THE INFLUENCE OF SULPHATE ION ON THE CRITICAL PITTING CORROSION TEMPERATURE OF 316 STAINLESS STEEL IN AQUEOUS SOLUTION CONTAINING CHLORIDE ION
    LIAO Jiaxing; JIANG Yiming; WU Weiwei; ZHONG Cheng; LI Jin; SONG Hongwei
    Acta Metall Sin, 2006, 42 (11): 1187-1190 . 
    Abstract   PDF (635KB) ( 1064 )
    The influence of sulphate ion on the pitting corrosion behavior of 316 stainless steel has been studied by measuring the relationship of corrosion current and temperature in 0.5wt.% chloride ion solution at different concentration of sulphate ion under constant applied potentials. The results showed that with the increase of sulphate ion concentration, the passivation current of 316 stainless steel increased and the Open Circuit Potential of 316 stainless steel decreased; When the concentration of sulphate ion is less than 0.42wt.%, the critical pitting temperature of 316 stainless steel is lower than the value without sulphate ion, and when the concentration of sulphate ion is more than 0.42wt.%, the critical pitting temperature is higher than that value. The inhibition and acceleration effect of sulphate ion on the pitting corrosion was discussed by analyzing the mechanism of the ion-competitive adsorption.
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    Effect of Mo Content on the Microstructure and Stress Rupture of a Ni Base Single
    MA Wenyou; HAN Yafang; LI Shusuo; ZHENG Yunrong; GONG Shengkai
    Acta Metall Sin, 2006, 42 (11): 1191-1196 . 
    Abstract   PDF (1187KB) ( 1176 )
    Abstract: Ni-base single crystal superalloys were prepared by screw selecting method. And the effects on microstructures and stress rupture properties of three kinds of Mo content superalloys with 2%, 3%, 4% were investigated, separately. The results showed that three as-cast structures of the alloys were composed of γ and γ′ phases. After heat treatment, alloy with 4% Mo content began to precipitate µ phase. The µ phase of alloy with 4% Mo content precipitated abundantly and grew, while alloy with 3% Mo content only a few µ phase and 2% Mo content without µ phase after heat exposure at 1100℃/500h. The µ phase was mainly composed of element Mo, Re, W, Cr, Co, Nb etc., in which the tendency of forming µ phase of Mo was the strongest, Re, W ,Cr took the second place and Co, Nb was the weakest. A lot of precipitation of stick-shaped µ phases damaged high temperature stress rupture properties of alloys. A few µ phase didn’t decrease high temperature stress rupture properties of alloys, on the contrary, improved them due to the solid solution strengthening effect of Mo. Therefore, the optimum Mo content should be 3wt.% for the based composition alloy Ni-5Cr-10Co-4W-3Re-5.6Al-8Ta-1Ti-0.5Nb.
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    Effects of TiC Films on the Rolling Contact Fatigue Life and Mechanical Properties of Bearing Steel
    LIU Hongxi; WANG Langping; WANG Xiaofeng; HUANG Lei; TANG Baoyin
    Acta Metall Sin, 2006, 42 (11): 1197-1201 . 
    Abstract   PDF (924KB) ( 1059 )
    ABSTRACT Titanium carbide (TiC) film is synthesized by plasma immersion ion implantation and deposition (PIII&D) technique on AISI52100 bearing steel surface. Testing include plan-view optical microscopy (OM), X-ray diffraction (XRD), friction and wear behaviors, rolling contact fatigue life and nanoindentation measurements. XRD patterns show that titanium carbide phase is formed in the film, and the microhardness of treated samples is higher than that of substrate. Rolling contact fatigue failure tracks were observed and analysised using conventional light microscope. Coated rolling elements failed in Surface wear or adhesive delamination, or a combination of these two modes depending upon the substrate bias voltage, implanted pulse width, treatment time and surface roughness. Results indicate that the maximum RCF life of the treated sample prolong by 5.5 times at a Hertzian stress level of 5.1GPa and 90% confidence level, respectively. Comparison with the substrate, the maximum microhardness and elastic modulus of treated specimen is increased by 28.4% and 12.1%, respectively. The friction coefficient decreased from 0.95 to 0.15 under identical wear conditions. This remarkable fatigue performance appears to be due to a combination of improved microstructure, adhesion, hardness and surface topography. Therefore, the PIII&D is regarded as one of promising technologies for improving the RCF life and mechanical properties of bearing.
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    Softening Mechanism of Boron—Bearing Low--Carbon Hot Strips Produced by TSCR Route
    QIU Shengtao; XIAO Lijun; LIU Jiaqi; GAN Yong
    Acta Metall Sin, 2006, 42 (11): 1202-1206 . 
    Abstract   PDF (217KB) ( 1126 )
    The SPHC (Steel Plate Heat Commercial) hot strips containing 10ppm~50ppm B were produced in the simulation of TSCR production route in the laboratory,the effects of boron micro-alloying on the microstucture,precipitates and mechanical properties were investigated.The results showed that the grain-size scale of the SPHC hot strips containing 10ppm~50ppm B can attain to 7~8 grade,the mean grain size was up to 22~35μm, the yield strength decreased by 94Mpa.
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    GRAIN SIZE OF PLATINUM NANOFILMS FABRICATED BY EB-PVD AND ITS EFFECT ON THERMAL CONDUCTIVITY
    CAO Bingyang; ZHANG Qingguang; ZHANG Xing; TAKAHASHI Koji; IKUTA Tatsuya
    Acta Metall Sin, 2006, 42 (11): 1207-1211 . 
    Abstract   PDF (741KB) ( 809 )
    Six platinum films with thickness 15-62 nm have been fabricated by the method of electron beam- physical vapor deposition (EB-PVD). The grain sizes of the platinum nanofilms and its effect on the thermal conductivity have been studied experimentally. It is found that the grain size increases with the nanofilm thickness increasing and goes to a constant about 20 nm. The grain size is nearly comparable with the nanofilm thickness with the thickness less than 30 nm, while becomes much less than the nanofilm thickness with the thickness larger than 30 nm. Influenced by the size effect caused by the nanofilm interface and the grain boundary effect by the grain structure, the thermal conductivity of the platinum nanofilms is greatly lower than that of the bulk platinum. It is noted that the thermal conductivity of the studied platinum nanofilms increases with the thickness increasing and runs to 35 W/mK, which is much lower than that of the bulk material due to the grain boundary effect.
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    A NiCr--Based High Temperature Self Lubricating Coating PM304 Prepared by Powder Metallurgy
    DING Chunhua; WANG Yaping; ZHOU Jing'en
    Acta Metall Sin, 2006, 42 (11): 1212-1216 . 
    Abstract   PDF (871KB) ( 841 )
    PM304 composite comprised of NiCr (80/20) matrix (60 wt%) combined with Cr2O3 (20 wt%), Ag (10 wt%) and eutectic BaF2/CaF2 (10 wt%) as solid self-lubricants additives has been prepared by high-energy ball milling and powder metallurgy. Experimental results showed that the sintering temperature had great influence on relative density and tensile strength of the PM304 composite. The relative density and tensile strength of PM304 increased rapidly with the increase of sintering temperature from 800°C to 1100°C. The size of Cr2O3 and BaF2/CaF2 of PM304 composite sintered at 1100°C was less than 1 μm, and that of Ag particles was below 5 μm, the relative density was 94%, and the mean tensile strength 47 MPa, 33% greater than that of PS304.
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    Influence of Precipitated Direction of the Second Phase on Shape Memory
    WEN Yuhua; ZHANG Wei; LI Ning; XIE Wenling; WANG Shanhua
    Acta Metall Sin, 2006, 42 (11): 1217-1220 . 
    Abstract   PDF (806KB) ( 798 )
    To develop Fe-based shape memory alloys with high revovery strain free of training, the effects of direct ageing and strain ageing on the precipitation of second phases, the martensite transformation and the shape memory effect in an Fe-13.53Mn-4.86Si-8.16Cr-3.82Ni-0.16C alloy were investigated. The analysis of SEM and X-ray diffraction showed that after ageing lots of Cr23C6 precipitated and the precipitation of second phases through direct aging is unidirectional, while the precipitation of second phases through strain ageing is directional. At the same aging time, the amount of second phases through strain ageing is much more than that through the direct ageing, and the size of second phases is half of that through the direct ageing. The shape memory effect can be remarkably improved through both the strain ageing and strain ageing at the optimal aging time. The shape memory effect after strain ageing is much better than that after the direct aging at the same aging time. The Fe-based shape memory alloys with high revovery strain free of training can be fabricated through controlling the precipitation with direction of second phases.
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    Finite Element Simulation of the Effect of Welding Residual Stress on Hydrogen Diffusion
    JIANG Wenchun; GONG Jianming; TANG Jianqun; CHEN Hu; TU Sh; ong
    Acta Metall Sin, 2006, 42 (11): 1221-1226 . 
    Abstract   PDF (901KB) ( 1039 )
    A sequential coupling calculating method on hydrogen diffusion had been developed based on the finite element program-ABAQUS. Using this method, effect of welding residual stress on the hydrogen diffusion was numerically simulated for the as-weld condition and postweld heat treatment (PWHT) condition. The diffusion without the effect of stress was also taken into account and compared with those with stress. The results show that hydrogen will diffuse and accumulate in the higher stress region under the existence of welding residual stress gradient. A low hydrogen concentration valley exists near the heat-affected zone(HAZ), which is caused by the long-range diffusion of hydrogen to the high stress zone. After the PWHT, stress relaxation is obvious and the maximum stress is decreased about 50%, which influences the hydrogen diffusion and makes the hydrogen concentration be decreased about 40%. Therefore, decrease in the welding residual stress by PWHT can effectively reduce the hydrogen concentration in the weldment and the susceptibility of material to environment hydrogen cracking.
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    Microstructures and Mechanical Property of Low Carbon Manganese Steel With
    LI Long; DING Hua; DU Linxiu; SONG Hongmei; ZHENG Fang
    Acta Metall Sin, 2006, 42 (11): 1227-1232 . 
    Abstract   PDF (1056KB) ( 909 )
    Thermo-mechanical controlled process (TMCP) experiments with various finish rolling temperature (FRT) and coiling temperature (CT) have been carried out on a low carbon manganese steel at temperatures above Ar3. OM and TEM observations indicate that the ferrite in uniform distribution and a certain amount of bainite could be obtained. Deformation induced ferrite transformation (DIFT) occurred when the FRT decreased to 800℃. Accelerated cooling (60℃/s) to 400℃ (CT) refines the allotriomorphic ferrite grain but retards the nucleation of intragranular ferrite with its distribution on prior austenite grain boundary as well as the volume fraction of bainite increased, and the strength increased but the elongation decreased and yield ratio became much higher on the steel. The good combination of mechanical properties of the steel with grain boundary allotriomorphic ferrite/banite could be gained by controlling FRT (800℃-850℃), cooling rate (40℃/s) and CT (550℃), in which ferrite grain size was about 8-8.5µm and the volume fraction of bainite about 20%.
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