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

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    , Volume 42 Issue 7 Previous Issue    Next Issue
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    Research Articles
    theoretical and experimental standardization of strain hardening index in tensile deformation
    SONG Yuquan; GUAN Zhiping; MA Pinkui; SONG Jiawang
    Acta Metall Sin, 2006, 42 (7): 673-680 . 
    Abstract   PDF (693KB) ( 1292 )
    Based on state equation that stress is a function of strain and strain-rate, the differential constitutive equation during superplastic tensile deformation is deduced, and then the mechanical meaning of strain hardening index in the equation is interpreted. The constraint equation of strain hardening index is deduced, strain hardening indexes in typical deformation paths are defined, and their interrelations are gotten. Measuring formulae of strain hardening indexes in typical deformation paths and accurate measuring methods by numerical simulation are deduced. According to them, strain hardening indexes are experimentally measured, and measuring methods & results are elaborately analyzed. The results prove that: not only does strain hardening index be non-constant, but also has close relations with the changing rule of strain and deformation path; not only does strain hardening index have close relations with deformation path, but also with adopted measuring formula. Therefore, as strain hardening index is quoted, its corresponding deformation path should be shown clearly; when strain hardening index is measured, the measuring formula of its corresponding deformation path should be adopted.
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    Progress in Materials Characterization Technique Based on in Situ Neutron Diffraction
    XU Pingguang; TOMOTA Yo
    Acta Metall Sin, 2006, 42 (7): 681-688 . 
    Abstract   PDF (1278KB) ( 1107 )
    Neutron diffraction is an atomic- or molecular-level characterization technique of material structures and microscopic movements because neutron is an electronic neutral subatomic particle with certain magnetic moment, strong penetration, more sensitive to light elements than X-ray and electron. The in situ neutron diffraction as one of materials four-dimensional characterization techniques has been reviewed with much emphasis on its applications to metallic materials science, such as residual stress evaluation, plastic deformation mechanism, solid phase transformation and nanometer clusters.
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    Effects of Hydrogen on Shear Bands and Cracking in Zr Base Bulk Amorphous Alloy
    SHAN Guangbin; WEI Bingchen; LI Jinxu; QIAO Lijie; CHU Wuyang
    Acta Metall Sin, 2006, 42 (7): 689-693 . 
    Abstract   PDF (996KB) ( 816 )
    The effect of hydrogen on shear bands and cracking in bulk metallic glass of Zr65Al7.5Ni10Cu17.5 has been studied through in situ tensile and banding tests in SEM using a single-edge notched and smooth three-point samples. The results show that for either hydrogen-free or hydrogenated samples, shear crack will initiate and propagate along shear bands when shear bands grow a certain condition, and opening of shear crack under a tensile stress results in rapid fracture of samples. The characterless zone on the fracture is the shear band instead of fracture surface of shear crack. There is no essential difference between tensile and shear fracture surfaces. Hydrogen blistering will form after charging for a long time, if hydrogen blistering is very small or unformed, there is no evident effect of hydrogen on forming of shear bands and initiating of crack. If the hydrogen blistering is large, the shear crack will initiate at the early stage of growing shear band, resulting in brittle fracture under low stress.
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    CBED Study of Local Strain Distribution in  and  Phases of a Crept Ni Base Superalloy
    LÜ Zheng; F. Pyczak; H. Biermann; H. Mughrabi
    Acta Metall Sin, 2006, 42 (7): 694-698 . 
    Abstract   PDF (564KB) ( 645 )
    The high lateral resolution CBED method was applied to measure the local elastic strain distributions in the two phases g and g¢ of the monocrystalline nickel-base superalloy CMSX-6 crept at 980℃. CBED measurements show that there is a difference of elastic strain in the vertical and horizontal g channels, which is thought to be the driving force for rafting. An inhomogeneous distribution of elastic strains is also observed in the g¢ phase.
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    Phase transformation behaviour and kinetics of electrodeposition Ni-P amorphous alloys by X-ray analysis
    HONG Bo; JIANG Chuanhai; WANG Xinjian; WU Jiansheng
    Acta Metall Sin, 2006, 42 (7): 699-702 . 
    Abstract   PDF (616KB) ( 1046 )
    Crystallization process in Ni-P amorphous alloy during continuous heating was investigated using in situ X-ray diffraction (XRD) analysis. The results show that different phosphorous content brings the difference of crystallization temperature and metastable phases transformed during continuous heating. Four metastable phases NiP、Ni2P、Ni12P5、Ni5P2 were detected in crystallization process. The activation energy of phase transformation and the crystallinity were calculated using dates of XRD gained from crystallization process. Activation energies of NiP(133±15kJ/mol), Ni2P(172±19kJ/mol) and Ni3P(190±20kJ/mol) were less than the crystallization activation energy of Ni-P amorphous alloy and the self-diffusion activation energy of nickel. This evidence supported that the formation of transformation phases was dominated not only atom-jumping or diffusion but also ordered cluster-shearing deposition.
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    Research on Grain Refinement Mechanism in Undercooled Fe75Ni25 Alloy
    CHEN Yuzeng; YANG Gencang; LI Feng; LIU Ning; XIE Hui; ZHOU Yaohe
    Acta Metall Sin, 2006, 42 (7): 703-707 . 
    Abstract   PDF (945KB) ( 981 )
    The grain refinement mechanisms of undercooled Fe75Ni25 alloys were investigated by fluxing and cyclic superheating. Within the undercooling, T, range achieved, two kinds of grain refinement were observed. In combination with the calculation and the analysis of experiment results, the grain refinement mechanisms were elucidated. The results indicate that the first grain refinement, occurring if T>56K, can be ascribed to the breakup of dendrite-skeleton owing to remelting, whereas the second grain refinement was caused by recrystallization induced by the stress originating from the rapid solidification contraction with T>209K.
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    In Situ Observation on Movement And Agglomeration of Inclusion in Solid--Liquid Mush Zone During Melting of Stainless Steel AISI304
    LIANG Gaofei; WANG Chengquan; FANG Yuan
    Acta Metall Sin, 2006, 42 (7): 708-714 . 
    Abstract   PDF (1258KB) ( 1171 )
    The movement and agglomeration of inclusion in the solid-liquid (S-L) zone during melting of an AISI304 stainless steel has been observed in-situ by using a confocal laser scanning microscope. The results show that the inclusion particles move through the liquid channels formed by the remaining solid. The average movement rate is 80 μm/s when the volume fraction of remaining austenite is about 70 %. Near to absolute melting, the movement rate of the inclusion far away from S-L interface is higher than 1500 μm/s, and that nearby the interface is in the range from 50 μm/s to 200 μm/s. A metal layer (δ ferrite phase) has been observed on the melt surface. It has the crystal boundary and sub-boundary similar to ordinary metal. The inclusions have been adsorbed by the metal layer. The morphology of the visible inclusion transfers from granular to worm-like during melting. The inclusions attract severely with each other, as a result, they agglomerate and granulate close-by the metal layer.
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    Grain Boundary Character Distributions (GBCD) of Cold-Rolled Pb--Ca--Sn--Al Alloy
    WANG Weiguo; ZHOU Bangxin; FENG Liu; ZHANG Xin; XIA Shuang
    Acta Metall Sin, 2006, 42 (7): 715-721 . 
    Abstract   PDF (954KB) ( 1613 )
    Grain boundary character distribution (GBCD) of cold-rolled Pb-Ca-Sn-Al alloy during recovery and recrystallization was investigated by means of electron back scatter diffraction (EBSD).The results indicate straight ∑3 boundaries of over 60% (length fraction of total boundaries, the same as follows) are introduced in the alloy during recovery. Such boundaries are not distributed in the network of general high angle boundaries (HABs) and the GBCD are not optimized. Conversely, in the recrystallization, apart from ∑3 boundaries of over 65% , a fairly amount of ∑9 and ∑27 coincidence site lattice (CSL) boundaries are appeared. ∑9 and ∑27 boundaries along with a great deal of curved ∑3 boundaries are located in the network of HABs and the GBCD are optimized. Further discussion pointed out the straight ∑3 boundaries formed in recovery are <111>60°coherent twin boundaries, they are stable and immobile. While, the ∑3 boundaries developed in recrystallization comprised of not only coherent twin boundaries but also most of incoherent ones. The migration of incoherent ∑3 boundaries as well as the interaction between them result in the formation of ∑9,∑27 and other ∑3n (n is a positive integer) boundaries, and it is the root of GBCD optimization.
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    Microstructure and room-temperature dry sliding wear behaviors of Mo2Ni3Si/γ-Ni metal silicide alloy
    XU Yawei WANG Huaming
    Acta Metall Sin, 2006, 42 (7): 722-726 . 
    Abstract   PDF (1131KB) ( 920 )
    γ-Ni toughened Mo2Ni3Si/γ-Ni metal silicide alloy consisting of Mo2Ni3Si primary dendrites and the interdendrtic γ/ Mo2Ni3Si eutectic was designed and fabricated by the lasmeltTM process. Room temperature wear properties were evaluated under metallic sliding wear test conditions and the wear mechanisms were discussed. Due to the unique and strong covalent-metallic bonding of Mo2Ni3Si Laves phase and the toughening effect of γ, Mo2Ni3Si /γ alloy performed excellent wear resistance. The wear mechanisms can be concluded as follows: the softer γ/ Mo2Ni3Si eutectic was preferential worn during wear process; due to the serious preferential abrasion, partial Mo2Ni3Si primary dendrites that protruded the worn surface were cracked and detached when losing the support of ductile matrix; in addition, the protruded Mo2Ni3Si primary dendrites prevent the matrix from continuous abrasion and control the total wear rate.
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    Preparation and Property of Nanometer Cu--Sn Alloy Anode Material for Lithium--Ion Batteries
    REN Jianguo; HE Xiangming; JIANG Changyin; WAN Chunrong
    Acta Metall Sin, 2006, 42 (7): 727-732 . 
    Abstract   PDF (827KB) ( 1173 )
    A reverse microemulsion technique was applied to prepare nanometer lithium storage alloy. Nanometer particles of copper-tin alloy with amorphous structures were successfully prepared. Because the electrode pulverization problem can be relieved by its small particle size, nanometer copper-tin alloy anode had a good cycle performance. However, a great irreversible capacity was caused by the formation of a SEI layer on the surface of nanometer alloy and the contact resistance between nanometer particles resulted in the poor electric conductivity. It is proved by experiments that the match of particle size and conductive agent content has a great impact on the electrochemical performance of the nanometer copper-tin alloy anode. When the conductive agent content increased to 40%, the nanometer copper-tin alloy with particle size of 50-60nm presented the best performance.
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    Precipitation Behavior Of Cast ZC62 Magnesium Alloy
    LI Xiao; LIU Jiangwen; LUO Chengping
    Acta Metall Sin, 2006, 42 (7): 733-738 . 
    Abstract   PDF (985KB) ( 1066 )
    Microstructural studies had been carried out in the ZC62 magnesium alloys with the as-cast and solution-ageing treated states by means of optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The microstructure of the as-cast ZC62 magnesium alloys was composed of the Mg matrix and eutectic (Mg+CuMgZn), after solution treatment at 440℃, most nonequilibrium eutectic at the grain boundaries dissolved. The granular CuMgZn phase and a small amount of needle-like Mg(Zn,Cu)2 precipitated within the Mg matrix after ageing treatment at 200℃ for different hours, and the Mg(Zn,Cu)2 phase disappeared with the ageing hour increasing, and transformed into the CuMgZn phase. The formation mechanisum of alloy precipitated phases and their effects on ageing strengthening were also discussed.
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    Effect of Multiple Forging Process on the Microstructure and Properties of Magnesium Alloy
    GUO Qiang; YAN Hongge; CHEN Zhenhua; ZHANG Hui
    Acta Metall Sin, 2006, 42 (7): 739-744 . 
    Abstract   PDF (1016KB) ( 1070 )
    The effect of multiple forging process on the microstructure and properties of magnesium alloy was investigated in the present paper. The results show that using the method of multiple forging, a homogeneous microstructure with ultrafine grains(1~2µm)can be attained and mechanical properties of alloy can be significantly improved. The dynamic formation of new grains during the deformation can result from a series of strain-induced continuous reactions that are essentially similar to continuous dynamic recrystallization and the intercrossing deformation bands developed in the coarse grains are beneficial for grain refinement. The microstructure with fine dynamic recrystallized grains can be attained when the applied total strain εx exceeds the critical strain εc which is in the rage of 2~2.4. After that, it is difficult to get more grain refinement further. Fractography demonstrates that the as-cast alloys’ tensile fracture consists of quasi-cleavage fracture mixed a little shear fracture and the microstructure morphologies of the alloy after forging are ductile dimple. At the same time, the dimples increase and exist more homogeneously with the increase of strain.
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    A Coupled Model of Microsegregation and Ti--O Inclusion Precipitation During Solidification of Liquid Steel
    ZHANG Huiquan; ZHENG Shaobo; ZHENG Qing; LIU Zili; JIANG Guochang
    Acta Metall Sin, 2006, 42 (7): 745-750 . 
    Abstract   PDF (768KB) ( 818 )
    ABSTRACT Basing segregation of solute elements at solid-liquid interface, a coupled model of microsegregation and Ti-O inclusion precipitation during solidification of liquid steel is established by considering finite diffusion of solute elements in both liquid and solid phases. The calculation results by this model shows that the segregation degree of solute elements is suppressed greatly due to the precipitation of Ti-O inclusions during solidification. The inclusions can be uniformly dispersed in steel by controlling due oxygen content. The number of oxides increases and their size reduces with the increasing cooling rate. The radius of the oxides only reach 0.58μm and their number and size are uniformly dispersed in steel and help to improve steel properties by controlling the condition of CSP.
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    Experimental Simulation of N--EMBr on Strip Casting with Twin Roll
    LI Qisheng; DENG Kang; LEI Zuosheng; LI Weixuan; REN Zhongming
    Acta Metall Sin, 2006, 42 (7): 751-756 . 
    Abstract   PDF (1019KB) ( 764 )
    A model for simulating suppression of level fluctuation in mold of twin-roll strip caster with nozzle electromagnetic brake (N-EMBr), which imposed stationary magnetic field and direct current in nozzle, was established. Momentum of metal liquid in nozzle and level fluctuation in twin-roll pool were measured under different conditions, including immerging depth of nozzle, current and magnetic field. The experiment results showed that momentum of liquid metal, amplitude and frequency of fluctuation all were decreased with current increasing. It was found that N-EMBr technique for fluctuation suppression is effective to twin-roll strip casting mold.
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    Temperature Distribution Simulation and Neck Evolution of Powder Particles During Spark Plasma Sintering
    LIU Xuemei; SONG Xiaoyan; ZHANG Jiuxing
    Acta Metall Sin, 2006, 42 (7): 757-762 . 
    Abstract   PDF (944KB) ( 964 )
    In the paper, temperature distribution in the powder particles during SPS was simulated and the process of neck evolution was studied. A model has been developed to simulate the heat transfer behavior during SPS process. By using the pure spherical copper particles as an example, the temperature distribution and the neck size evolution of the powder particles have been studied. There is a greatly inhomogeneous distribution of the temperature in the particle, and the growth rates of the necks are different. The obtained simulation results show a good agreement with the experimental measurements, which confirmed the reasonability of the model developed in the present work. By the modeling and experimental studies, the intrinsic mechanisms of neck formation and neck growth are well explained.
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    Enhancing Adhesion Between Diamond Film and WC--Co Substrate
    LI Jianguo; Hu Dongping; MEI Jun; LIU Shi; LI Yiyi
    Acta Metall Sin, 2006, 42 (7): 763-769 . 
    Abstract   PDF (1460KB) ( 849 )
    The effect of Murakami solution and H2 plasma treatment on the morphology and structure of tungsten carbide-cobalt has been investigated by the use of SEM and XRD. Then these pretreated tungsten carbide-cobalt tools were coated with multiple diamond film. Finally, the adhesion between diamond film and WC-Co substrate was evaluated with indentation method and drilling test. The Murakami solution treatment induced uniform corrugation on tungsten carbide-cobalt surface, as a result, the critical load of diamond film of this treatment is about 1.5kN examined with indentation method, but the diamond coated drill pretreated with Murakami solution has a bad cutting performance. H2 plasma treatment promoted WC grain more coarse and closed, thus, the critical load of diamond film of this treatment is more than 1.5kN and the diamond coated drill pretreated with H2 plasma demonstrated excellent cutting performance.
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    EFFECT OF ZIRCONIUM CONTENT ON PRECIPITATION OF SILICIDE IN TI-1100 ALLOY
    XU Feng; LI Geping; YANG Rui M. Varlioglu; P. Nash
    Acta Metall Sin, 2006, 42 (7): 770-776 . 
    Abstract   PDF (873KB) ( 1134 )
    Morphology and distribution of silicide in Ti-1100 alloy with different zirconium content were observed by TEM. Isopleths at 0.45wt %( 0.76at %) of the Ti–Zr–Si system for Ti-1100 alloy was deduced according to the TEM results, isothermal sections of Ti–Zr–Si system phase diagram and concerned references. Both the TEM observation and the Isopleths show that silicide resolve temperature increases as Zr content increase. Moreover, as Zr content increased, dissolvability of silicon in titanium declines. These changes result in silicide coarsening, silicide volume fraction increase and precipitation position change.
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    Preparation and Compression Properties of Fe--C--Si--B--P--Cr--Mo--Al Bulk Metallic Glass
    LI Hongxiang; YI Seonghoon; ZHANG Xinfang; WANG Xiaodong
    Acta Metall Sin, 2006, 42 (7): 777-780 . 
    Abstract   PDF (253KB) ( 803 )
    A new cast Fe-based bulk metallic glass Fe69C7.0Si3.5B4.8P9.6Cr2.1Mo2.0Al2.0 (at%) with maximum thickness of 5mm in diameter was successfully prepared by copper mold casting technique using industrial raw materials. The thermal stability and crystallization behavior were investigated by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and x-ray diffraction (XRD). The results showed that the glass transition temperature Tg, supercooled liquid region △Tx (△T x = T x -Tg), reduced glass transition temperature Trg (Tg/Tl) and glass-forming ability parameter g (Tx/(Tg+Tl)) were measured to be 784K, 27K, 0.601, 0.388, respectively. The double-stage crystallization process of Fe69C7.0Si3.5B4.8P9.6Cr2.1Mo2.0Al2.0 amorphous ribbons is due to the first precipitation of single a-Fe phase followed by the precipitation of Fe3C, Fe2P, FeB, Fe2B phases simultaneously. The bulk glassy alloy exhibits very high fracture strength of about 3870MPa, Young’s modulus (E) of 177GPa, elastic strain(εe) of 0.021 and plastic strain (εp) of 0.0029.
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    Simulation of Effects Of Grain Scale on Al Polycrystal Strength Using Strain Gradient Plasticity Concept
    ZHOU Li; LI Shouxin; KE Wei
    Acta Metall Sin, 2006, 42 (7): 781-784 . 
    Abstract   PDF (619KB) ( 731 )
    In order to investigate the effect of grain size on the material strength,in this work, we use the classical plasticity theory and the mechanism-based strain gradient plasticity theory to simulate the stress-strain of Al polycrystals of different grain size. The results indicate that the plastic work hardening of the stress strain curves predicted by the mechanism-based strain gradient constitutive equation indeed increase with the decrease in grain size. The stress-strain curve for grain diameter d=20um is slightly above that predicted by classical plasticity theory, this is to show further that with the increase of grain size, the contribution of strain gradient to the stress is decrease. At the same time, the fit line of the yield strength and grain size by the computing is consistent with the Hall-Petch line.
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