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

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    , Volume 31 Issue 5 Previous Issue    Next Issue
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    STUDY OF CLEAVAGE FRACTURE SURFACE OF TiAl ALLOYS IN NANOMETER SCALE
    ZHANG Yue; CHU Wuyang; WANG Yanbin; QIAO Lijie; XIAO Jimei(Universityof Science and Technology Beijing; Beijing 100083); WANG Zhonghuai; BAI Chunli)(Institute of Chemistry; Chinese Academy of Sciences; Beijing 100080)
    Acta Metall Sin, 1995, 31 (5): 191-196. 
    Abstract   PDF (472KB) ( 533 )
    The cleavage fracture surfaces of Ti_3Al and Ti-24Al-11Nb samples after tensile tests in air were studied with a scanning tunnel microscope(STM). Many details in nanometer scale were revealed on the fracture surfaces by STM, such as nanometer scale steps, dimples and vacancies. The study of the details on the fracture surfaces will be helpful to the study of the mechanism of fracture.
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    EFFECT OF DISLOCATION DENSITY ON DUCTILE-BRITTLE TRANSITION TEMPERATURE IN BULK Fe-3%Si SINGLE CRYSTALS
    BAO Jinsheng; YANG Cheng; HA Kuanfu(Jilin University; Changchun 130023)
    Acta Metall Sin, 1995, 31 (5): 197-200. 
    Abstract   PDF (257KB) ( 565 )
    The ductile-brittle transition temperature of Fe-3% Si single crystals under tensile tests with strain rate varying from 5 × 10~(-1) s~(-1) to 5 ×10~(-3) s~(-1) was investigated. It was shown that the transition temperature is nearly independent of the dislocation density difference of two order of magnitude, but quite different from that in Fe-3 % Si polycrystal.
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    VALENCE ELECTRON STRUCTURE OF Fe_2B PHASE AND ITS EIGEN-BRITTLENESS
    LI Musen; FU Shaoli(Shandong University of Technology; Jinan 250014). XU Wandong(Tianjin University; Mianjin 300072); ZHANG Ruilin. YU Ruihuang(Jilin University; Changchun 130023)
    Acta Metall Sin, 1995, 31 (5): 201-208. 
    Abstract   PDF (496KB) ( 649 )
    The valence electron structure of Fe_2B phase was studied on the basis of Yu's empirical electron theory of solids and molecules.The values of valence electrons on every bond in an atomic coordinate cluster were calculated by the method of bond length difference(BLD). The results showed that the bonds between Fe-Fe atoms along (220] direction were strongest, of which the value of valence electrons n_A=0.3852 and the bond energy E_A = 1 5.7372 kJ / mol, The bonds between B-B atoms along [002] direction were weaker, of which n_D = 0. 1 392 and E_D = 4.5052 kJ/ mol. A space bond network of Fe_2B crystal was built,so the cause of the eigen-brittleness could be translated by a heterogeneity of the bond distribution. Comparing experimental results to theoretical analysis, it came to the conclusion that there was a conformability between them.
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    TEM OBSERVATION OF SECONDARY HARDENING PROCESS IN Ni10Co14 STEEL
    LING Bin; ZHONG Ping; ZHONG Bingwen; GU Baozhu(Beijing Institute of Aero nautical Materials; Beijing 100095)
    Acta Metall Sin, 1995, 31 (5): 209-215. 
    Abstract   PDF (501KB) ( 835 )
    The changes of microstructure in the tempering process of the Ni10Co14 steel have been studied by TEM. Special attention has been paid to the microstructures near the peak of the tempering curve. Mo_2C nucleared and grew along dislocation lines, martensitic lath boundaries, and some of them in situ transformed from M_3C at ferrite / cementite interface. The maximum strength in Ni10Co14 steel was achieved when the steel was tempered at 440℃ for 5 h. The strengthening of the steel was mainly attributed to the combination of the delayed dislocation recovery of the martensitic matrix and coherent precipitation of the Mo_2C particle.
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    EFFECT OF Nb AND Ti CONTENTS ON MICRO-SEGREGATION OF J-90 ALLOY
    WANG Anchuan; LI Yiyi; LI Dongfa; YANG Ke; FAN Cungan; SHI Changxu(Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1995, 31 (5): 216-222. 
    Abstract   PDF (595KB) ( 581 )
    EMPA has been performed to investigate the distribution of Nb and Ti in the solidification structure of J-90 alloys with different contents of Nb and Ti. With increasing of Nb content in the alloy, Nb tends to be seriously segregated, while distribution of Ti becomes more and more homogeneous, but when the content of Ti in the alloy being increased, segregations of Nb and Ti are all lessened. By increasing contents of Nb and Ti in the alloy, partition coefficients of Nb and Ti at the beginning of solidification are all increased. It was found by comparison that difference between the highest and the lowest content of an element after solidification is a more proper parameter for description of elemental segregation which is dependent on the content of elements and the elemental partition coefficient. The fact that k_(Nb) and k_(Ti) increased with increasing of Nb and Ti contents in the alloys indicated that when contents of trace elements (such as P etc.) were lowered, on the solute-rich layer during solidification there would be less these trace elements while contents of easy-segregated elements, such as Nb and Ti, could increased. As a consequence, k_(Nb) and k_(Ti) would increase and micro-segregation of Nb and Ti would decrease.
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    EFFECT OF THERMOCHEMICAL PROCESSING WITH HYDROGEN ON MICROSTRUCTURE OF SUPER-α2 ALLOY
    LIAO Bo; WANG Tiansheng; YANG Ke; YUAN Hui; XIAO Furen;LI Yiyi(Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015)(Yanshan University; Qinhuangdao 066004)
    Acta Metall Sin, 1995, 31 (5): 223-228. 
    Abstract   PDF (385KB) ( 467 )
    Quantitative study of the thermochemical processing(TCP) with hydrogen on the microstructure of Super-α2 alloy has been carried out by means of quantitative phase analysis of X-ray diffraction. The results showed that the microstructure consists of α2, B2 and O phases and the formation of O phase can be effectively promoted by TCP with hydrogen. The volume fraction of O phase in the alloy was found to be increased with hydrogen content. Discussion on mechanism of the effect of TCP with hydrogen on microstructure of Super-α2 was also presented.
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    TRANSVERSE RUPTURE STRENGTH OF Ni BONDED Ti(C, N) CERMET AND FRACTAL DIMENSION ANALYSIS OF ITS FRACTURE SURFACES
    LIU Ning; ZHAO Hingzhong; JIANG Laizhu; LUO Huiguo; HU Zhenhua; CUI Kun(Huazhong University of Science and Technology; Wuhan 430074)
    Acta Metall Sin, 1995, 31 (5): 229-235. 
    Abstract   PDF (456KB) ( 636 )
    The relationships among the fractal dimension of fracture surfaces, transverse rupture strength and microstructure of Ti(C, N) based cermets have been studied. The microfracture fractal model of cermets and the estimated fractal dimension formula of fracture surfaces have been proposed. The experimental results have shown that the logarithm value of transverse rupture strength, lgσbb , increases with the increase of fractal dimension DF, and has a linear equation relationship. The change of microstructure has a considerable effect on the fractal dimension. The measured fractal dimension depends on the choice of measuring unit. There is an upper critical measuring unit εK′to the Ti(C, N) based ceimets.
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    INDENTATION MEASUREMENT ON HARDNESS DISTRIBUTION WITH A SINGLE LOADING-DISPLACEMENT CURVE
    HOU Genliang; LIU Junhai; XU Kewei(State Laboratory.for Mechanical Behaviourof Materials; Xi'an Jiaotong University; Xi'an 710049)
    Acta Metall Sin, 1995, 31 (5): 236-240. 
    Abstract   PDF (331KB) ( 788 )
    A method calculating the hardness distribution in a whole indentation depth with a single load-placement curve was proposed. The theory is based on the experimental results that the loading pattern keeps constant and the initially unloading slope is proportion to the indention depth. This is applicable to study the hardness distribution at the surface layer of a bulk material. Both theoretical and experimental results agree well.
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