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

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    IN SITU TEM STUDY OF DISLOCATION EMISSION AND MICROCRACK NUCLEATION FOR α-Ti AFTER ADSORBING Hg
    SU Yanjing; LU Hong; WANG Yanbin; CHU Wuyang (Department of Materials Physics; University of Science and Technology Beijing; Beijing 100083)
    Acta Metall Sin, 1998, 34 (4): 337-344. 
    Abstract   PDF (3515KB) ( 631 )
    Using a special constant deflection device, the change in dislocation configuration ahead of a loaded crack tip for α-Ti before and after adsorption of Hg atoms, and the initiation of Hg--induced microcrack have been observed in TEM, as well as the in situ extension in TEM without Hg. The results showed that chemisorption of Hg atoms could facilitate dislocation emission and motion. When the dislocation emission and motion developed into a critical situation, a microcrack induced by liquid metal would nucleate from the main crack tip or/and in dislocation free zone (DFZ), and propagate in cleavage mode. During in site extension in TEM without the liquid metal, only when dislocation emission and motion induced by thermal activity and applied stress reached a certain critical condition, microcrack would nucleate but not blunt into a void.
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    STM STUDY ON THE SURFACE RELIEF EFFECTS ASSOCIATED WITH WIDMANSTATTEN FERRITE
    BO Xiangzheng; FANG Hongsheng; WANG Jiajun; WANG Zhenghua (Department of Materials Science and Engineering; Tsinghua University; Beijing 100084)
    Acta Metall Sin, 1998, 34 (4): 345-350. 
    Abstract   PDF (1755KB) ( 619 )
    Surface relief accompanying Widmanstatten ferrite formation in an Fe-0.37Calloy was investigated by scanning tunneling microscopy (STM). It was discovered that the surface relief due to Widmanstatten ferrite formation appears to be of tent-shaped type, or complex type.The evolution of surface relief of Widmanstatten ferrite can be more interpreted by ledgewisegrowth mechanism rather than by displacive mechanism. The height of relief is 70-450 nm, and the maximum shape deformation is ca. 0.36.
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    MICROSTRUCTURE FEATURES IN DIRECTIONALLY SOLIDIFIED Ni_3Al ALLOY AFTER HIGH TEMPERATURE DEFORMATION
    GU Yuefeng; LIN Dongliang; SHAN Aidang (The Public Laboratory of State Education Commission for High Temperature Materials and High Temperature Tests; Shanghai Jiaotong University; Shanghai 200030)(CHEN Jiaguang; HU Fan; CAO Hanqing (Shanghai Baoshan Institute of Iron and Steel; Shanghai 201900)
    Acta Metall Sin, 1998, 34 (4): 351-355. 
    Abstract   PDF (1735KB) ( 589 )
    Optical microscopy, transmission electron microscopy and scanning electron microscopy were used to examine microstructure features of the directionally solidified Ni3Al alloy deformed under tension at high temperature. The results show that initial columnar grain boundaries have not obviously changed during the deformation under higher strain rate and there are no substructure within the columnar grains. When strain rate is lower, the initial columnar grain boundaries firstly change into sawtooth shape and then evolve into small grain belts with increasing strain during superplastic deformation. The average grain size in belt is about 15 mm containing both low angle grain boundaries and high angle grain boundaries. It is suggested thata continuous recovery and recrystallization process took place during superplastic deformation in DS Ni3Al alloy.
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    MICROSTRUCTURE AND MICROSEGREGATION OF Ni-BASE SINGLE CRYSTAL SUPERALLOY SOLIDIFIED AT MEDIUM COOLING RATE
    DU Wei; WEI Pengyi; LI Jianguo; FU Hengzhi (State Key Laboratory of Solidification Processing; Northwestern Polytechnical University; Xi'an 710072)SUN Jiahua(Central Iron and Steel Research Institute; Ministry of Metallurgical Industry; Beijing 100081)
    Acta Metall Sin, 1998, 34 (4): 356-361. 
    Abstract   PDF (2930KB) ( 782 )
    With the help of high temperature-gradient directional solidification equipment (HGDS), the microstructure and microsegregation of Ni-base single crystal superalloy CMSX-2 solidified at the cooling rates from below 1 K/s to 20 K/s were investigated. The morphology of γ' precipitates and γ/γ'eutectic in the specimens were examined. The results show that, withthe increase of the cooling rate, the primary dendrite arm spacing is greatly refined to 38 μm,just as one-tenth as that by HRS processing. The microsegregation increases and then decreaseswith the increase of cooling rate. In the superfine columnar dendrite , the γ' precipitate is very fine, the amount of γ/γ' eutectic is much fewer and its' size is very small.
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    EFFECT OF Ni_xAl_yTi_z REFINER ON GRAIN STRUCTURES OF CAST SUPERALLOY K4169
    ZHENG Jianbang; DING Hao; GUO Yiping; LIU Lin (Department of Applied Physics; Northwestern Polytechnical University; Xi'an 710072)LIU Wei; LI Xingjian (Liming Engine Manufacturing Company; Shenyang 110043)
    Acta Metall Sin, 1998, 34 (4): 362-366. 
    Abstract   PDF (2758KB) ( 747 )
    Grain size and dendrite morphologies of Fe-Ni based superalloy K4169 were investigated with the melt addition of NixAlyTiz refiner. It is found that the grain size of ingotscan be refined obviously to 0.1-0.2mm, close to the order of ASTM 1-3, by lowering the melting homogeneous treatment temperature during the melting and casting process. In addition, the microstructure of grains can be transferred from dendritic to cellular due to the addition ofrefiner at the same cooling condition. The addition of NixAlyTiz refiner has the advantages of little influence on the freezing characters, alloy composition as well as phase constitution.
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    STUDY ON THE PLATELET PHASE IN AN YTTRIUM-CONTAINING LOW EXPANSION SUPERALLOY
    WANG Rongming; LI Chunzhi; PING Dehai; YAN Minggao (Beijing Institute of Aeronautical Materials; Beijing 100095)(Laboratory of Atomic Imaging of Solids; Institute of Metal Research; The Chinese Academy of Sciences;Shenyang 110015)(Beijing Laboratory of Electron Microscopy; The Chinese Academy of Sciences; Beijing 100080)
    Acta Metall Sin, 1998, 34 (4): 367-372. 
    Abstract   PDF (2369KB) ( 621 )
    The resistance to stress accelerated grain boundary oxygen embrittlement (SAGBO) and the notch-bar rupture life in Fe-Ni-Co low expansion superalloy have been improved with increasing platelet precipitates in the matrix and grain boundaries by trace yttrium element addition. The crystal structure of the platelet phase and its orientation relationship with the matrix have been determined using transmission electron microscopy, convergent beam electron microscopy, X-ray energy dispersive spectrum, X-ray diffraction analysis and high resolution transmission electron microscopy. It has a CaCu5 type crystal structure (space groupP6/mmm) with lattice parameters a=0.498 nm and c=0.408 nm. The crystallographic orientation relationship between the phase and the matrix is found to be (111)γ
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    HYDROGEN INDUCING AMORPHIZATION OF Ti-Fe SYSTEM IN MECHANICAL ALLOYING
    REN Shan; HONG Lan; ZHANG Jinxiu (Department of Physics; Zhongshan University; Guangzhou 510275)LU Manqi; HU Zhuangqi (State Key Lab of RSA; Institute of Metal Research; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (4): 373-377. 
    Abstract   PDF (428KB) ( 470 )
    The solid reactions and structures of Ti+Fe and Ti+Fe+TiH2 during mechanical alloying were studied by using XRD, DSC etc. The results show that hydrogen can induce amorphization of TiFe in MA. The characteristic temperatures of amorphous TiFe(H) phase, such as structure relaxation and crystallization temperatures, are lower than that of the amorphousTiFe phase synthesized by mechanical alloying.
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    HIGH TEMPERATUER LOW CYCLE FATIGUE OF DZ40M COBALT-BASE SUPERALLOY
    JIANG Wenhui; YAO Xiangdong; GUAN Hengrong; HU Zhuangqi ( Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)(Shenyang Polytechnic University; Shenyang 110023)
    Acta Metall Sin, 1998, 34 (4): 378-383. 
    Abstract   PDF (2754KB) ( 514 )
    Stress controlled low cycle fatigue tests on directionally solidified cobalt-basesuperalloy DZ40M have been conducted at 900℃ in ambient atmosphere. DZ40M superalloy exhibits high low cycle fatigue resistance. The fractography observation indicates that preferentially oxidized carbides at specimen surface act as crack initiation sites, and carbides in matrix have the retardation effect on crack propagation. Oxdation effect reduces alloy ductility, thatpromotes crack propagation. High temperature low cycle fatigue damage of DZ40M superalloyresults from the interaction of thermo--mechanical fatigue and enviromental okidation.
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    PERMEATION PROCESS OF MOLTEN IRON IN A SELF-BAKING CARBON BLOCK
    HU Xiaojun (Department of Physicochemistry; University of Science and Technology; Beijing 100083)XUE Xiangxin; DUAN Peining (School of Materials and Metallurgy; Northeastern University; Shenyang 110006)HUANG Xiaoyu(Ironmaking Work; Anshan Iron & Steel Company; Anshan 114021)
    Acta Metall Sin, 1998, 34 (4): 384-387. 
    Abstract   PDF (1082KB) ( 619 )
    Permeation process of the molten iron in a self-baking carbon block (SBCB)was studied at both 1450 and 1500℃. The permeation degree of the samples was observed and confirmed by EPM. A dependence of permeation depth on time, h2=11773t(1450℃), was obtained and a permeation model, was established by utilizing the theory of permeationand fluid dynamics, and a porous structure parameter relevant to the permeation was defined.Also, the influnces of temperature and graphitizing degree on the permeation were discussed.
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    DATABASE SOFTWARE DEVELOPMENT FOR ACTIVITY AND INTERACTION MRAMETER OF ALLOY SYSTEMS
    LUO Lihua; DING Xueyong; GUO Dan; CAO Wenbin; ZOU Zongshu; WANG Wenzhong (School of Materials and Metallurgy; Northeastern University; Shenyang 110006)( University of Science and Technology Beijing; Beijing 1100083)
    Acta Metall Sin, 1998, 34 (4): 388-392. 
    Abstract   PDF (454KB) ( 846 )
    The software package of activity and interaction parameter in alloy systems was developed with both the recommendation values edited by Japan Society for the Promotion of Science and the predicted values of Ding Xueyong's model calculation, which can supply the user the wide interaction parameters and can calculate the activity coefficient and activity for almostany element.
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    TEMPERING PRECIPITATES OF STEEL 1.25Cr-0.5Mo AND THEIR EFFECTS ON ITS HYDROGEN ATTACK RESISTANCE
    SU Tiejian; LUO Xinghong; FAN Cungan; LI Yiyi (Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)CHEN Xiao; GUO Aimin (Wuhan Iron and Steel Company; Wuhan 430080)Correspondent: SU Tiejian; Fax: 024-3891320; Tel. 024-3843531-55445)(Manuscript received 1997-04-30; in revised form 1997-07-08)
    Acta Metall Sin, 1998, 34 (4): 393-399. 
    Abstract   PDF (2166KB) ( 609 )
    Studies were made on the tempering precipitates and their effects on hydrogen attack (HA) resistance of the medium-temperature HA-resistant Steel 1.25Cr-0.5Mo. It was shown by TEM of carbon extraction replicas that, with increasing tempering temperature, more carbides were precipitated and coarsened. When tempered at 520℃ and 620℃, almost only M3C was precipitated. When tempered at 670℃, M3C was the main precipitate with a small amount of M23C6. While tempered at 710℃, M23C6 was the main precipitate with a small amount of M3C. It was observed by SEM that,after charging hydrogen, samples tempered at 620℃ were seriously attacked by hydrogen, which resulted in great drop of strength and hardness.While no apparent HA phenomenon was observed for samples tempered at 520℃, 670℃ and710℃, but rupture strength of samples tempered at 520℃ was greatly decreased. It is related that large quantity of unstable M3C precipitated along grain boundaries, and the C-rich and Cr-poor regions for the sample tempered at 620℃ appeared, resulted in the HA degradation of the material.
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    THE INFLUENCE OF MISMATCH SPEED RATIO ON TEXTURE DEVELOPMENT IN CROSS SHEAR ROLLED 3% SILICON STEEL
    LIU Gang (School of Materials and Metallurgy; Northeastern University; Shenyang 110006; School of Chemical Science and Engineering; Liaoning University; Shenyang 110036)QI Kemin; WANG Fu; WANG Gang; LIANG Zhide (School of Materials and Metallurgy; Northeastern University; Shenyang 110006)
    Acta Metall Sin, 1998, 34 (4): 400-405. 
    Abstract   PDF (568KB) ( 691 )
    Commercial grain oriented silicon steel was cold rolled by cross shear rolling (CSR) with different mismatch speed ratios (MSR), followed by industry annealing. The effects of MSR on the texture development were analyzed. Experimental Results show that the MSRexerts little effect on the surface layers and the area near the higher speed roll, but more influenceon the middle section. With increasing the MSR, the texture configuration at the subsurface andthe middle section can be improved significantly. In this process the texture development exhibitsthe "inherence ", but does not influence the final results. The effect of secondary recrystallizationannealing in a CSR process is similar to that in conventional rolling process, i.e. Goss texture grows abnormally, and form the only texture component. Under different MSR being used, thefinal texture and the magnetic properties of samples are resemble, so the MSR can be selectedwithin a certain range.
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    INTERDIFFUSION IN LOW TEMPERATURE ANNEALED CoN/CN SOFT X-RAY MULTILAYER MIRRORS
    BAI Haili; JIANG Enyong (Department of Applied Physics; Tianjin University; Tianjin 300072)
    Acta Metall Sin, 1998, 34 (4): 406-411. 
    Abstract   PDF (492KB) ( 480 )
    The interdiffusion in the amorphous CoN/CN soft X-ray multilayer is investigated quantitatively by monitoring the enhancement of the first order modulation peak onannealing in the temperature range of 473-523 K. The effective interdiffusion coefficient measured is as low as 10-25m2s-1. The comparison with the results of Co/C system indicates that the following three features are noticeable: (1) the critical wavelengths of interdiffusion obtained are 2.00-2.04 nm at temperatures ranging from 473 to 523 K and equal to those of Co/C multilayers within the experimental error, indicating that the interdiffosion behaviour in the CoN/CNmultilayers still depends on the thermodynamic properties of the Co--C system, (2) the effectiveinterdffesivities and macroscopic diffusion coefficiellts are lower, and (3) the activation energy ofdiction is higher. The results imply that it is possible to improve the thermal stability of Co/Cmultilayer by doping with nitrogen.
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    OSCILLATORY COUPLING OF THE Co-Nb/Cr MULTILAYERED FILMS
    LOU Jianxin; YAN Shishen; LIU Yihua (Department of physics; Shandong University; Jinan 250100)
    Acta Metall Sin, 1998, 34 (4): 412-415. 
    Abstract   PDF (394KB) ( 775 )
    Co-Nb/Cr multilayered films were prepared with the rf-sputtering method. The magnetic properties of the samples were studied by a micropro cessor-controlled vibrating-sample magnetometer. When the charging Ar pressure PAr=2.67 Pa, an oscillation between ferromagnetic and antiferromagnetic coupling with the thickness of Cr layers was found, and the spontaneous magnetization Ms remains constant basically. When PAr=0.67 Pa, the value of Ms shows an oscillatory behaviour, which may be related to the oscillatory variation of the paramagnetic component in the ferromagnetic layers.
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    NUMERICAL SIMULATION OF TIG WELD POOL BEHAVIOR UNDER THE ACTION OF PULSED CURRENT
    WU Chuansong (Institute of Joining Technology; Shandong University of Technologyl Jinan 250061)ZHENG Wei; WU Lin(College of Materials Science and Engineering; Harbin Institute of Technology Harbin 150001)
    Acta Metall Sin, 1998, 34 (4): 416-422. 
    Abstract   PDF (612KB) ( 988 )
    A mathematical model is established for simulating the TIG(Tungsten Inert Gas) weld pool behavior in pulsed TIG welding. It was analyzed how the pulsed current affects the fluid flow and heat transfer in a TIG weld pool and the pool geometry. The computed results show that the volume of weld pool is sensitive to the action of pulsed currellt, the gradiellt ofthe surface tension is the main driving force for the fluid flow in pulsed TIG weld pool, andthe fluid velocity field changes periodically with the pulsed current. The computer vision-basedexperiment system is used to measure the varying process of the weld pool width in a ptilsedcycle. The predicted weld pool width is in agreement with the measured one.
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    COMPUTER STUDY OF MAGNETIZATION IN NANOCOMPOSITE MAGNETS
    CHU Yelong; XIONG Liangyue; SUN Xiaokai (Institute of Metal Research; The Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1998, 34 (4): 423-430. 
    Abstract   PDF (805KB) ( 761 )
    The computer simulation of magnetization process of a single powder particle of the Nd2Fe14B/α-Fe nanocomposite magnet has been performed. Three types of hysteresis loops have been observed at different conditions: Stoner-Wohlfarth like type, contracted loop and normal hysteresis loop with a good rectangularity. The behavior of the reduced remanence, the intrinsic coercivity and the change of maximum magnetic energy product with the grain size, a,and the content of the soft phase, fm, have been studied. For the model nanocomposite magnetsof fm=40% and the grain size a=25 nm, the optimum value of (BH)max=375 kJ/m3 is attained.It is remarkably enhanced in comparison with the maximum of (BH.)max=264 kJ/m3 of the pure Nd-Fe-B magnet.
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    MICROSTRUCTURES AND PROPERTIES OF IN SITU SYNTHESIS Ni/Ni-Al MULTILMER COMPOSITES
    WANG Huabin; HAN Jiecai; DU Shanyi (Center of Composite Materials; Harbin Institute of Technology; Harbin 150001)
    Acta Metall Sin, 1998, 34 (4): 431-436. 
    Abstract   PDF (1845KB) ( 659 )
    Full-dellsity Ni/Ni-Al multilayer composites were successfully fabricated by in-situ reaction of Ni and Al foils at 620℃ for 1 hour under 1 MPa pressure, and then diffusion annealing for 4 hours at 750℃, 950℃ and 1150℃ respectively under 5 MPa pressure in vacuum.Ductile Ni layer in composites can greatly improve room-temperature fracture toughness bymicrocracks bridging and blunting. After annealing at 750℃ and 950℃, Al2O3 at the surface of Al foils before reaction remains at the interface of bilayer Ni2Al3 as inclusions, which makesinterface poorly bonded. But after annealing at 1150℃, Ni3Al layer is well-bonded with Ni and NiAl layer. So, the composites show significantly strain-hardening and plastic flow, its mean fracture strength and strain are 786 MPa and 12.8% respectively.
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    MICROSTRUCTURE AND ALLOY ELEMENT DISTRIBUTION OF DIRECTIONALLY SOLIDIFITED Al_2O_3/Al-4.5Cu METAL MATRIX COMPOSITES
    CHU Shuangjie; WU Renjie; YANG Chunsheng; XU Dong (The State Key Laboratory of Metal matrix Composites; Shanghai Jiaotong University; Shanghai 200030)
    Acta Metall Sin, 1998, 34 (4): 437-442. 
    Abstract   PDF (1658KB) ( 675 )
    The microstructure and the change of alloy elements distribution of Al2O3/Al-4.5 Cu composites have been studied by use of the newly developing ZMLMC directional solidification apparatus, experimental results showed: At solidification rate v=16.7 μm/s, the microstructure of directionally solidified Al2O3/Al-4.5Cu composites, was cell morphologies, there were no Al2O3 particles in the cell structures, as solidification rate was increased to 49.8μm/s, its microstructureswere dendrites morphologies, particles were uniformly distributed in dendrites; with increase of solidification rate, the primary and secondary dendrite arm spacings decreased, the distributionof Cu element in the vicinity of liquid-solid interface was also changed regularly.
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    THE INTERFACE MICROSTRUCTURE OF A B_4C_p +SiC_w/MB15 MAGNESIUM BASED COMPOSITE
    WU Zhengan; GU Mingyuan; CHEN Yu; ZHANG Gooding (The State Key Laboratory of MMCs; Shanghai Jiaotong University; Shanghai 200030)
    Acta Metall Sin, 1998, 34 (4): 443-448. 
    Abstract   PDF (2878KB) ( 722 )
    The magnesium alloy (MB15) matrix composites reinforced by the hybrid ofthe boron carbide particle and the silicon carbide whisker were fabricated with vacuum pressure infiltration and hot extrusion techniques. The interface microstructure of the composite has been studied using analytical electron microscope (equipped with EDS, EELS). Experimental results showed that the chemical reaction 4Mg(1)+B2O3(1)=MgB2(s)+3MgO(s) took place during infiltration, and produced magnesium diboride (MgB2) phase and MgO microcrystallites. Due to this interface reaction, liquid magnesium wetted boron carbide particle. Moreover, the surface of boron carbide particle had a serrated periphery, thus a strong interfacial bonding was formed,which resulted in excellent mechanical properties of the composite. Because of the flowabilityof boron chide, the same interfacial reaction also took place at the SiCw/Mg interface region,where the SiC whisker is near a boron carbide particle. When the SiC whisker is far from a boroncarbide particle, the SiCw/Mg interface is straight with β' (MgZn2) precipitates on it.
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