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

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    , Volume 31 Issue 9 Previous Issue    Next Issue
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    GENERAL EXISTENCE OF LEDGES OF INITIAL BAINITES IN Cu-Zn-Al ALLOYS
    LI Chunming(Department of Modern Applicd Physics;Tsinghua University;Beijing 100084); FANG Hongsheng; WANG Jiajun; ZHENG Yankang (Tsinghua University; Beijing 100084)
    Acta Metall Sin, 1995, 31 (9): 381-386. 
    Abstract   PDF (433KB) ( 593 )
    The microstructures of bainites in three composition Cu-Zn-Al alloys formed at 250, 300 and 350℃ were investigated by means of transmission electron microscopy (TEM). The results show that all the initial bainites formed in different alloys at different temperatures are with three-dimensional ledges on the broad faces and/ or at the growth edges of α1 plates but without internal stacking faults, which proves that ledges exist generally on bainites in Cu-Zn-Al alloys and that the growth of bainites is governed by a diffusion-controlled ledgewise mechanism.
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    INVESTIGATION OF SURFACE RELIEF WITH BAINITE AND MARTENSITE BY SCANNING TUNNELING MICROSCOPY
    FANG Hongsheng; YANG Zhigang(Department of Materials Science & Engineering; Tsinghua University.Beijing 100084); WANG Jiajun; ZHENG Yankang (Tsinghua University; Beijing 100084)
    Acta Metall Sin, 1995, 31 (9): 387-392. 
    Abstract   PDF (400KB) ( 676 )
    Scanning tunneling microscopy (STM) was first employed to study the surface relief accompanying bainite and martensite transformation in an Fe-C-Cr steel. With the exclusive vertical resolution of STM, a result indicates that the surface relief associated with bainite is a group of surface reliefs related to subplates, subunits and sub-subunits, and not of invariant plane strain (IPS) type, which is obviously different from that of martensite,and implying that bainite does not form by shear mechanism.
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    MICROTWINNING DEFORMATION IN PST TiAl CRYSTAL
    LIU Yi; WANG Dening; CHEN Da; LIN Dongliang; (Department of Materials Science; Shanghai Jiaotong University;Shanghai 200030) CHEN Shipu (Shanghai Jiaotong University; Shanghai 200030; State Key Laboratory of Solid State Microstructures of Nanjing University; Nanjing 210008); LIU Zhiyuo (Nanjing University; Nanjing 210008)
    Acta Metall Sin, 1995, 31 (9): 393-398. 
    Abstract   PDF (434KB) ( 618 )
    The behaviour of microtwinning in TiAl PST crystal has been investigated by TEM. The results show that the microtwinning plane is(111) and microtwin results from the movement of (1/6)[112] Shockley partials. The microtwinning can moved across the twin-related interface of lamellar TiAl phase without changing the twinsystem. These results indicate that the twin-related interface of TiAl can not hinder the microtwinning effectively. The effects of microtwinning on the deformation of PST crystal have been discussed.
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    TEM STUDY ON DEFORMATION MICROSTRUCTURE IN A Fe-Mn-Si-Cr-Ni SHAPE MEMORY ALLOY
    RONG Lijian; (Institute of Meial Research; Chinese Academy of Sciences; Shenyang 110015) PING Dehai; LI Yiyi; SHI Changxu (Lab of Atomic Imaging of Solids; Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1995, 31 (9): 399-404. 
    Abstract   PDF (399KB) ( 632 )
    Effects of elements Cr and Ni on the c/a ratio and stress-induced ε martensite microstructure in Fe-Mn-Si alloy have been investigated, by using X-ray and analytic electron microscope. The results show that by addition of Cr and Ni, c/a ratio in Fe-Mn-Si alloy has been increased from 1.620 to 1.656 and this is favourable to the formation of fec deformation twin. The penetration process of ε martensites on different {111}plane can be avoided through the formation of ε martensite in fcc twin, which is responsible for the better shape memory effect in Fe-Mn-Si-Cr-Ni alloy.
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    CHARACTER OF NUCLEATION AND BRANCHING OF STRENGTHENING PHASE IN Ni-NbC ALLOYS
    LI Shunpu; (Institute of Physics; Chinese Academy of Sciences; Beijing 100080) ZHAO Deqian; CHEN Xichen (Institute of Physics; Chinese Academy of Sciences; Beijing 100080); BARABASH O M; OSHKADEROV S P (Institute of Metal Physics; Academia Sinica. Kiev; Ukraine 252142)
    Acta Metall Sin, 1995, 31 (9): 405-410. 
    Abstract   PDF (415KB) ( 589 )
    This paper studied the Ni-NbC alloy morphology and orientation character under the effect of impurity Mo, by using optical and scanning electron microscope(SEM)and X-ray preferred orientation analysis. Result has shown that the growing primary crystals have two kinds of morphologies: hexahedron and octahedron, while their preferred growth orientation is <111> and <100> , respectively. During the growth of eutectic alloy, NbC phase branched mainly on the preferred growth direction, while the effect of defect was minor.
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    DYNAMIC RECOVERY AND RECRYSTALLIZATION OF COMMERCIAL ALUMINIUM UNDER TORSION AT ELEVATED TEMPERATURES
    SHEN Jian; (Department of Materials Science and Engineering; Central South University of Technology; Changsha 410083) ZHANG Xinming; ZHANG Siqi; YIN Zhimin; LU Bin (Central South University of Technology; Changsha 410083); SONG Hengzao; SHU Xianjin (Chengdu Seamless Steel Tube Mill; Chengdu 610069)
    Acta Metall Sin, 1995, 31 (9): 411-416. 
    Abstract   PDF (487KB) ( 704 )
    Hot torsion testing was conducted on commercial aluminium at 300-500℃ and constant surface strain rate of 5.0 s-1 to study the dynamic recovery and dynamic recrystallization. The microstructural observations under OM and TEM show that the dynamic recovery is the only operative restoration mechanism if the deformation temperatures are below 400℃, and substructure consists of approximately equiaxial subgrains.The material, however, is mainly softened by dynamic recrystallization when torsion temperatures exceed 450℃ . The fine and homogeneous recrystallized grains, which are different from the coarse initial grains, develops over the gauge length of the specimens after large strain of about 3.85.The essential features of the torsional equivalent stress-strain behaviours are consistent with that of periodically oscillating flow. A Hall-Petch relationship was satisfied by linear regression between the reciprocal of average diameter of subgrains and Zener-Hollomon parameters.
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    FORMATION OF BIMODEL DISTRIBUTION OF RE-RICH SECOND PHASE PARTICLES IN RAPIDLY SOLIDIFIED Ti-55 ALLOY
    LI Geping; (Institute of Metal Research; Chinese Academy of Sciences;Shenyang 110015) LI Dong; LIU Yuyin; HU Zhuangqi (Institute of Metal Research; Chinese Academy of Sciences; Shenyang 110015)
    Acta Metall Sin, 1995, 31 (9): 417-421. 
    Abstract   PDF (297KB) ( 511 )
    The rapid-solidified Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd (Ti-55) high temperature alloy heat-treated 5h at 980℃ has been studied by TEM. The results show that the distribution of the RE-rich second phase particles is bimodel, the amount of the smaller particles (20─80 nm in diameter) is considerably larger than that of the large particles (200─300nm in diameter). Based on a diffusion-controlled growth kinetics equation, the formation mechanism of the bimodel distribution of the RE-rich second phase particles in the alloy is explained by using the disturbing theory.
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    INITIATION AND GROWTH BEHAVIOURS OF CONTACT FATIGUE CRACKS
    SHA Jiangbo; JING Hiaotian; LOU Bingzhe; (Department of Materials; Past Box No.719; Xi'an University of Technology; Xi'an 710048) SHEN Fusan (Xi'an University of Technology; Xi'an 710048)
    Acta Metall Sin, 1995, 31 (9): 422-430. 
    Abstract   PDF (708KB) ( 604 )
    The initiation and growth behaviours of contact fatigue cracks under point contact and different f conditions (where f is the coefficient of friction) were studied by stress analysis and SEM observation, and the general and typical characteristics of contact fatigue failure were demonstrated. Results show that under the boundary lubrication condition, the contact fatigue crack initiates at the surface and grows into the subsurface in a manner governed by mode II loading, and the orientation of the crack path is controlled by the maximum shear stress at the advancing crack tip. On condition f=0, the typical crack growing path consists of 4 stages having the shape of the letter U, while it undergoes 3 stages shaped like the letter V on condition f=0. Generally, the contact fatigue failure results from a series of continuous pitting composed of a stochastic combination of the different stages of a typical crack growth process under conditions f≠0.
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