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

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    NUMERICAL SIMULATION OF THE INTERLAMELLAR SPACING OF Al-CuAl_2 EUTECTIC
    ZHANG Weiqiang;YANG Yuansheng; HU Zhuangqi (State Key Lab of RSA; Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (1): 1-6. 
    Abstract   PDF (431KB) ( 896 )

    In this paper, a time-dependent model of directionally solidified Al-CuAl2 eutectic system is numerically calculated according to the theory of lamellar eutectic growth. The computed minimal and maxiamal interlamellar spacings correspond well to the experimental results,the lamellar spacing increases due to melt flow in solidification, and such structure is unstable as the spacing exceeds the maximum. Moreover, the lower the growing rate, the greater the effect of fluid flow.

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    SIMULATION OF SOLIDIFICATION BEHAVIOR IN SPRAY DEPOSITED PREFORMⅠ. Theoretical Analysis
    ZHANG Jishan; CUI Hua; DUAN Xianjin; SUN Zuqing; CHEN Guoliang (State Key Laboratory of Advanced Metals and Materials; University of Science and Technology Beijing; Beijing 100083)
    Acta Metall Sin, 1998, 34 (1): 7-12. 
    Abstract   PDF (363KB) ( 570 )
    Solidification in preform is an important stage during spray forming process, which shows great effect on the final formation of microstructure within the spray deposited preform. It is essential to make a full understanding of the solidification process to optimize the spray forming process and obtain desired preform microstructures. In this study, a concept of"vertual"solidification layer is applied to establish a theoretical model to simulate the solidification process in preform during spray forming, which will provide a theoretical tool for the further analysis of the solidification behavior in spray deposited preform.
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    SIMULATION OF SOLIDIFICAFION BEHAVIOR IN SPRAY DEPOSITED PREFORM Ⅱ.Calculation Results For Al-Cu Alloy
    ZHANG Jishan;CUI Hua; DUAN Xianjin; SUN Zuqing; CHEN Guoliang (State Key Laboratory of Advanced Metals and Materials; University of Science and Technology Beijing; Beijing 100083)
    Acta Metall Sin, 1998, 34 (1): 13-18. 
    Abstract   PDF (438KB) ( 614 )
    According to the solidification model in the spray formed preform proposed in the first part of this study, the solidification behavior of typical Al-Cu alloy is calculated and discussed.The result shows that processing parameters such as deposition rate and spray temperature at deposition, and material thermal physical properties such as surface heat transfer coefficient have apparent effects on solidification process in preform. Under the same deposition thermodynamic conditions such as the thermodynamic state of the sprat cone just before depositing on the surface of the preform, temperature of deposition surface will vary significantly as the processing parameters and material thermal physical properties change. Therefore the temperature of deposition surface should be taken as the major factor for spray processing control, and the formerly proposed principle for spray forming processing control should be reconsidered.
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    DIFFUSION-CONTROLLED PHASE TRANSFORMATIONS OF Al_(65)Cu_(20)Cr_(15) QUASICRYSTALLINE PARTICLES/AI MATRIX COMPOSITES
    QI Yuhong;ZHANG Zhanping;HEI Zukun (Institute of Metal and Technology; Dalian Maritime University; Dalian 116026)QUAN Mingliu (Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)DONG Chuang (Dalian University of Technology; 116024)
    Acta Metall Sin, 1998, 34 (1): 19-23. 
    Abstract   PDF (1621KB) ( 701 )
    Diffuse phase transformations of A165Cu20Cr15 quasicrystalline particles/AI composite were studied by TEM for the first time. It shows that SIQC quasicrystalline particles transform into FIQC, (DQC+DA)+θand θ phases respectively at the different hot press temperatures of 600, 650 and 700 ℃. During diffusion-controlled phase transformation, SIQC phase transforms through the transitional FIQC, DQC, DA phase to the stable θ phase.
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    TWINS AND ITS FORMATION MECHANISM IN LOWER META-BAINITE
    LUAN Daocheng; WEI Chengfu;YANG Ge (Department of Materials Science and Engineering; Sichuan Institute of Technology; Chengdu 611744)
    Acta Metall Sin, 1998, 34 (1): 24-30. 
    Abstract   PDF (3125KB) ( 607 )
    By TEM it has been confirmed that twin substructures exist in lower metabainite in silicon-containing steel. A large number of twins was found in bainitic midribs for first time. Twins in midribs (M-M) as well as retained austenite (Ar) are deformation twins formed by coordinating uniform shear deformation as bainitic ferrite lath grows, twins in bainitic ferrite (BF)mainly are those inherited in retained austenite as BF thickens by shear mechanism in broad face. and twin planes correspond to the interface ledges, which shows ledges can not migrate along side direction of broad face. Based on the results, a model of twin formation in lower meta-bainite was suggested.
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    TEM INVESTIGATION ON MICROSTRUCTURES OF EUTECTOID CEMENTITE IN HIGH CARBON LOW ALLOY STEELS
    ZHU Xiaodong;LI Chengji; ZHANG Shouhua (Department of Materials Science and Engineering; USTB; Beijing 100083)ZOU Ming; SU Shihuai (Panzhihua Iron and Steel [Group] Company; Panzhihua 617067)
    Acta Metall Sin, 1998, 34 (1): 31-38. 
    Abstract   PDF (3529KB) ( 688 )
    The eutectoid cementite in several rail steels has been studied by means of TEM.It was found that the eutectoid cementite lamellae arc not of homogeneous structure but contain some ferrite sub-lamellae with different widths and same orientation. The continuity of the eutectoid cementite lamellae was reduced when the ferrite sub-lamellae were incorporated. The planar indices of the ferrite sub-lamellae are found usually close to {211}F.Some contrast fringes observed at the cementite/ferrite interface were analyzed and compared with the sub-lamellae in the eutectoid cementite. The formation mechanism of ferrite sub-lamellae in eutectoid cementite was also discussed.
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    DEFORMATION BEHAVIOR OF γ-TiAl SINGLE CRYSTALS AT DIFFERENT TEMPERATURES
    WU Donghai;HU Gengxiang (Department of Materials Science; Shanghai Jiaotong University; Shanghai 200030)INUI Haruyuki; YAMAGUCHI Masaharu (Kyoto University; Kyoto 606-01; Japan)
    Acta Metall Sin, 1998, 34 (1): 39-44. 
    Abstract   PDF (438KB) ( 636 )
    The plastic deformation behavior of γ-TiAl(Ti-56%Al) single crystals was studied by compression in the temperature range of-196-1100℃ along seven crystal orientations: [001],[152] , [021], [233], [191], [251] and [110]. The profile of the yield stress-temperature curves measured can be divided into three parts: in the temperature range of-196-600℃, the yield stress first decreases rapidly with increasing temperature followed by a plateau above room-temperature.The yield stress then shows an anomalous increase with increasing temperature above 600 ℃and reaches a peak between 700-1000℃, depending on crystal orientations. Above the peak temperature, the yield stress again decreases rapidly with increasing temperature. Below the peak temperature, the deformation mode is {111}<110] ordinary slip only for [021] orientation and {111}<101] superlattice slip for other orientations. Above the peak temperature, the deformation modes are: {111}<112] twinning, {111}<112] superlattice slip or ordinary slip. The planes for ordinary slip can be {111}, {110) or (001), depending on crystal orientations.
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    PHASE COMPOSITION OF ZrM_2(M=Mn, V, Ni)HYDROGEN STORAGE ALLOYS
    LEI Yongquan;ZHANG Wenkui;YANG Xiaoguang;WANG Qidong (Department of Materials Science and Engineering; Zhejiang University; Hangzhou 310027)LU Guanglie (Central Laboratory; Hangzhou University; Hangzhou 310028)
    Acta Metall Sin, 1998, 34 (1): 45-50. 
    Abstract   PDF (490KB) ( 728 )
    The phase component and abundance in Zr(Mn0.45-xNi0.55)2 (x=0.10-0.40)Laves phase hydrogen storage alloy were investigated by X-ray multiphase Rietveld analysis. The results of Rietveld analysis showed that all the alloys were composed of C15, C14 type Laves phase and the residual phases such as Zr9M11 and ZrM phase. Laves phase and Zr9M11 phase existed in the studied composition range, however, ZrM phase only appeared in the range of x=0.20-0.40. When x=0.05 - 0.15, the alloys consisted of C15, C14 and Zr9 M11 phase, in which the main phase was of C15 type. At x=0.20-0.40, the alloys consisted of C15, C14, Zr9 M11 and ZrM, in which the main phase was the mixture of C15 and C14 phase. The phase abundance of Zr9 M11 had a little variation in the whole range, however, that of ZrM phase showed a bigger fluctuation. The lattice parameters of each phase appeared in alloys showed a tendency to increase as V content increases. On the basis of the calculation of averaged numbers of outer electrons, the occurrence of Laves phase was found to have correlation with electron factors.
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    FATIGUE LIVES OF GRAIN BOUNDARY AND COMPONENT CRYSTALS IN A COPPER BICRYSTAL
    ZHANG Zhefeng; LI Guangyi; WANG Zhongguang; LI Shouxin (State Key Laboratory of Fatigue and Fracture of Materials; Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (1): 51-56. 
    Abstract   PDF (2367KB) ( 724 )
    Cyclic tension-tension deformation was carried out on a copper bicrystal which consists of a single and a double slip oriented component crystal. The grain boundary of the bicrystal is nearly perpendicular to the stress axis during cyclic deformation. The S-N curves of grain boundary and component crystals were respectively determined. By comparison of fatigue lives between component crystals and grain boundary, it was found that the fatigue lives of grain boundary were lower than those of component crystals, however, the fatigue lives of two component crystals showed no obvious difference under the same cyclic stress. Surface observation by SEM indicated that the probability of initiating fatigue cracks in copper bicrystal increased in the order of double, single slip oriented component crystals and grain boundary under the same cyclic load amplitude.
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    THE CREEP-DAMAGE BEHMIOUR OF A SINGLE CRYSTAL NICKEL-BASE SUPERALLOY
    TIAN Sugui;ZHOU Huihua; ZHANG Jinghua; YANG Hongcai; XU Yongbo; HU Zhuangqi (State key Laboratory for Fatigue and Fracture of Materials; Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)(Department of Materials Science and Engineering; Northeastern University; Shenyang 110006)(Department of Metal Materials Engineering; Shenyang Polytechnic University; Shenyang 110023)
    Acta Metall Sin, 1998, 34 (1): 57-62. 
    Abstract   PDF (3064KB) ( 552 )
    The microstructures in the late stage of the creep have been observed by means of SEM and TEM. The results show that the microstructure corresponding to the macro-slip in the third stage of the creep is that a large number of dislocations shear into the rafted γ' phases,decreasing creep resistance of superalloy. The slip steps are produced on the slip lines by the interaction of the multi-slip. The direct reason of the creep fracture is that the rafted γ'phase is twisted and the micro-cracks are emerged in alloy due to the continuous cross-slips.
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    3D TOPOGRAPHY OF FRACTURED SURFACES AND MECHANICAL PROPERTIES UNDER INSTRUMENTED IMPACT LOADING
    ZHU Ping;CHEN Bingsen (Department of Mechanical Engineering; Tsinghua University; Beijing 100084)
    Acta Metall Sin, 1998, 34 (1): 63-69. 
    Abstract   PDF (1128KB) ( 662 )
    The dynamic fracture properties of P460NLl steel were tested under instrumented impact loading at different test temperatures. The 3D topography of fractured surfaces was reconstructed and quantified by the means of SEM stereo pairs, image processing and analysis, and computer vision. It was shown that measured 3D roughness indexes Rs, Rq and Rmax have good positive relations to the crack propagation part of absorbed impact energy. Although fractal behavior had been checked out on the fractured surfaces, the fractal dimension was found nonsensitive to the fracture mode and mechanical properties. The geometric characteristics of fractal fractured surfaces should be quantified in fractal dimension together with absolute parameters.
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    FATIGUE CRACK GROWTH RATES AND FATIGUE THRESHOLDS OF CENTRIFUGAL SPRAY DEPOSITED Ti-48Al-2Mn-2Nb
    CHEN Wenzhe;ZHANG Sa;QIAN Kuangwu (Department of Materials; Fuzhou University; Fuzhou 350002)GU Haicheng (Institute of Materials; Xi'an Jiaotong University; Xi'an 710049)WANG Zhongguang (State Key Laboratory for Fatigue and Fracture of Materials; Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (1): 70-74. 
    Abstract   PDF (1316KB) ( 594 )
    The fatigue crack growth rates and fatigue thresholds of a Ti-48Al-2Mn-2Nb intermetallics, which was formed by a special spray forming technique so--called" centrifugal spray deposition" (CSD) under a low vaccum condition, were investigated at ambient temperature.Threepoint bend fatigue specimens with notch length of 0.5 mm were prepared and compressioncompression fatigue tests were carried out under load control. The results show that CSD samples with lamellar-structure have a better fatigue crack growth resistance and a higher fatigue threshold than that of HIP (hot isostatic pressing) samples with duplex structure. The relationship of da/dNversus △K could be shown as: da/dN=3.8×10-12 (△K)6 for CSD samples and da/dN=1.9 ×10-17 (△H)12 for HIP samples, and the fatigue thresholds of CSD and HIP samples are 10.5 MPa m1/2 and 7.5 MPam1/2, respectively.
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    CLASSIFICATION OF THERMODYNAMIC PROPERTIES OF BINARY METALLIC MELTS ACCORDING TO THEIR PHASE DIAGRAMS
    Zhang Jian (Institute of Metallurgy; University of Science and Technology Beijing; Beijing 100083)
    Acta Metall Sin, 1998, 34 (1): 75-85. 
    Abstract   PDF (888KB) ( 885 )
    After combining investigation of thermodynamic properties of binary metallic melts with their phase diagrams, it has been found that when the calculating models of mass action concentrations of metallic melts are formulated according to their main phase diagrams (i.e.phase diagrams involving compound formation, involving peritectic, involving saturated phase,involving solid solution and involving eutectic), the calculated thermodynamic properties (mass action concentrations) will rigorously obey the mass action law, except for the continuous solid solution obeying Raoult's law.
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    MAGNETIC PROPERLIES AND STRUCTURE OF A MIXTURE OF α-Fe and Fe_3N DURING MECHANICAL ALLOYING PROCESS
    XU Hui;HE Kaiyuan;CHENG Lizhi (Department of Materials Science and Engineering; Northeast University; Shenyang 110006)
    Acta Metall Sin, 1998, 34 (1): 86-90. 
    Abstract   PDF (358KB) ( 400 )
    The X-ray diffraction was used to monitor the structure change of a mixture of α-Fe and Fe3N powders during ball milling. The change of saturation magnetization of the mixture powder was also measured. The results showed that Fe3N decomposed quickly with increasing milling time and disappeared after milling for 2 h, and some N atoms soluted in α-Fe. After milling for 24 h, a stable supersaturation solid solution was obtained. N content was about 0.290%-0.346%. With increasing milling time, the grain size decreased. After milling for 24 h, grain size reached a constant which is about 8 urn. The sites of N atoms nearby Fe atom changed during milling, so the saturation magnetization of the mixture powder initially decreased, but began to increase when milling time exceeded 5 h, and reached a constant when milling time exceeded 24 h.
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    AMORPHOUS FLUX MATERIALS FOR FLUX-CORED WIRE
    YU Shengfu;LIU Shunhong;XIE Mingli; LI Zhiyuan (Department of Materials Science and Engineering; Huazhong University of Science and Technology; Wuhan 430074)WANG Jie(Nantong Import and Export Commodity Inspection Bureau of the P.R.C; Nantong 226005)
    Acta Metall Sin, 1998, 34 (1): 91-94. 
    Abstract   PDF (326KB) ( 605 )
    The principle and technology to produce amorphous flux for flux-cored wires by the sol--gel process were introduced in detail. Amorphous flux powders have been made from Ti(OC4H9)4 and Si(C2H5)4 and analysed with X--ray diffraction, TGA and DTA. The results show that the amorphous fuel powders produced by the sol-gel process have homogeneous chemical compositions, low residual hydrogen content and less moisture adsorption, which can meet the need of automatic welding production and has a good future for the development and applications.
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    PROPERTIES OF A HIGH SILICON ALUMINIUM ALLOY POWDER PREMRED BY HIGH PRESSURE WATER ATOMIZATION
    LI Yuanyuan; ZHANG Datong; XIA Wei;ZHANG Wen; WEN Liping (Mechanical and Electronic Engineering Department; South China University of Technology; Guangzhou 510641)
    Acta Metall Sin, 1998, 34 (1): 95-99. 
    Abstract   PDF (1858KB) ( 776 )
    Al-30%Si alloy powder was prepared by high-pressure water atomization, and its oxygen content, particle size, morphology and microstructure were studied. Results show that the water atomization process can prepare fine particle size, even size distribution, low oxygen content powder. Due to rapid solidification, the silicon phases were greatly fined and the base-phase was reinforced, as compared with Al-30%Si cast alloy.
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    ANALYSIS OF THE FORMATION MECHANISM OF TiB_2 PARTICULATE FABRICATED BY IN SITU REACTION IN MOLTEN ALUMINIUM
    YANG Bin; WANG Yuqing;ZHOU Benlian (Institute of Metal Research; The Chinese Academy of Sciences;Shenyang 110015)(Department of Mechanical and Electronic Engineering; Nanchang University; Nanchang 33002)(International Center for Materials Physics; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (1): 100-106. 
    Abstract   PDF (1907KB) ( 711 )
    By making use of a technique in which TiB2 particulates are formed by an in situ reaction in molten aluminium, TiB2/Al composites have been fabricated. The formation mechanism of TiB2 particulate was studied with XRD and SEM. The results show that (1) the heat generated by the reaction 3Al1+Tis→Al3Ti is one of reasons for igniting the reactions Al3Ti+2B→ 3Al+TiB2 and Ti+2B →TiB2, (2) diffusion, solution-precipitation mechanisms occur during this process and (3) both theoretical and experimental results have shown that the effect of aluminium content in the preform on the formation mechanism of TiB2 particulate is much obvious. When the mole fraction of aluminium in the preform exceeds 43.5%, TiB2 particulates are formed by a diffusion mechanism, and the morphology of the particulates is approximately spherical. A part of TiB2 particulates is formed by a solution-precipitation mechanism when the mole fraction of aluminium is lower than 43.5%, and the TiB2 particulates have grown up to square and multilateral shape. A number of square and multilateral TiB2 particulates with growing steps have been clearly observed with SEM.
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    CREEP DEFORMATION AND FRACTURE OF DISPERSOIDS AND SiC PARTICULATES REINFORCED Al BASE COMPOSITES
    ZHOU Qing; MA Zongyi; ZHAO Jie; BI Jing; ZHU Shijie; WANG Fugang (Materials Engineering Department; Dalian University of Technology; Dalian 116024)(Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (1): 107-112. 
    Abstract   PDF (2021KB) ( 622 )
    Creep of dispersoids and SiC particulates reinforced aluminium base composites has been studied. Creep rate of the composites is 2-4 orders of magnitude lower than those of the matrix alloy. The creep stress exponent and activation energy of the composites are much larger than those of pure aluminium. The experimental data of creep has been analysed by the threshold stress approach. It is demonstrated that the creep of the composites is controlled by the lattice diffusion of aluminium.
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