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

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    , Volume 30 Issue 10 Previous Issue    Next Issue
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    CYCLIC DEFORMATION BEHAVIOUR OF Cu SINGLE CRYSTAL ORIENTED FOR DOUBLE SLIPS Ⅰ. Cyclic Hardening and Saturation
    GONG Bo; WANG Zhongguang; ZHANG Yiwei; LI Guangyi; ZHANG Tianyi(State Key Laboratory for Fatigue and Fracture of Materials; Institute of Metal Research; Chinese Academy of Sciences; Shenyang)(Manuscript received 16 March; 1994)
    Acta Metall Sin, 1994, 30 (10): 431-438. 
    Abstract   PDF (606KB) ( 657 )
    The cyclic hardening and saturation behaviour of Cu single crystals oriented for double slips ([034], [117]) and single slip ([125]) were investigated at plastic resolved shear strain amplitudes (γpl) over a range of 10~(-4)─ 10~(-2). The initial cyclic hardening behaviour of [034] crystal is found to be similar to that of [125] crystal. At γpl< 10~(-3), the cyclic hardening rate is lower and independent of γpl , reflecting the relative ease of primary dislocation multiplication. While at γpl> 10~(-3)', it increases significantly with increasing γpl, reflecting the dislocation interaction between primary slip and critical slip. [117] crystal shows much higher cyclic hardening rates at 10~(-4)<γpl < 5 × 10~(-3) as compared with two other crystals due to the strong dislocation interaction of primary and conjugate slips. Both [034] and [117] crystals display an obvious softening phenomenon after initial rapid hardening. The cyclic stress-strain curve (CSSC) of[034] crystal exhibits a plateau region, in which saturation shear stress is the same as that of [125] crystal. However, the upper limit of the plateau is lower (γpl~ 4.3×10~(-3)). The CSSC of [117] crystal is similar to that of polycrystal, showing almost no plateau. The saturation stress is monotonic function of γpl.Correspondent: GONG Bo, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015
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    CYCLIC DEFORMATION BEHAVIOUR OF Cu SINGLE CRYSTALS ORIENTED FORDOUBLE SLIP Ⅱ. Persistent Slip Bands and Deformation Bands
    GONG Bo; WANG Zhongguang; ZHANG Yiwei; LI Guangyi; ZHANG Tianyi(State Key Laboratory for Fatigue and Fracture of Materials; Institute of Metal Re-search; Chinese Academy of Sctences; Shenyang)(Manuscript received 16 March; 1994)
    Acta Metall Sin, 1994, 30 (10): 439-447. 
    Abstract   PDF (863KB) ( 771 )
    The surface morphologies of fatigued Cu single crystals with double slip orientations ([034], [117]) were investigated by optical and scanning electron microscopy. At plastic shear strain amplitude (γpl) below 10~(-3), the surface of [034] crystal is mainly covered by the persistent slip bands(PSBs) of primary slip, and the secondary PSBs only appear at the edge regions of the specimens with a volume fraction less than 1 percent. At γpl> 10~(-3), the secondary slip system becomes active on a large scale, particularly at region between primary PSBs, and two kinds of macro deformation bands (DBⅠ, DBⅡ) form with primary PSBs concentrated inside. [117] crystal shows a pronounced double slip phenomenon even at γpl~4.4 × 10~(-4). At γpl > 10~(-3), deformation bands also form similar to those of [034] crystal. The habit plane of DB Ⅰ is either parallel to (in [034] case) or near to (in [117] case) primary slip plane, while that of DBⅡ is perpendicular to the former one.The possible reason of the formation of deformation bands is discussed.Correspondent: GONG Bo, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015
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    EFFECTS OF HYDROGEN ATOMS OF INITIATION AND PROPAGATION OF CRACKS UNDER SLOW LOADING
    HAN Guangwei(Central Iron and Steel Research institute Ministry of Metallurgical Industry); SONG Yujiu; (Xi′an Jiaotong University)(Manuscript received 9 November; 1993; in revised form 3 June; 1994)
    Acta Metall Sin, 1994, 30 (10): 448-452. 
    Abstract   PDF (398KB) ( 638 )
    The effects of hydrogen atoms on crack initiation and propagation have been studied in normalized Cr-1Mo steel using in situ SEM tensile experiment. The results are found that the critical plastic deformation at notch root for initiation of ductile crack is reduced by charging hydrogen, and the crack propagation pattern is also changed from continuous growth on the plane of maximum shear stress to uncontinuous growth on maximum normal stress plane. Hydrogen induced plastic deformation has not been found, and the effect mechanisms of hydrogen atoms are analysized.Correspondent: HAN Guangwei, Department 5, Central Iron and Steel Research Institute, Ministry of Metallurgical Industry, Beijing 100081
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    PSEUDO-DENDRITE GROWTH CHARACTERISTICS OF γ′PRECIPITATES IN SINGLE CRYSTAL NICKEL BASE SUPERALLOY
    ZHANG Jinghua; YAO Xiangdong;ZHANG Zhiya; LI Yingao;GUAN Hengrong;HU Zhuangqi(Institute of Metal Research; Chinese Academy of Sciences; Shenyang)(Manuscript received 17 March; 1994)
    Acta Metall Sin, 1994, 30 (10): 453-462. 
    Abstract   PDF (817KB) ( 593 )
    An investigation has been made of the nucleation and growth characteristics of the pseudo-dendritic γ′precipitates in a single crystal nickel base superalloy which is directly aged after homogenizing and solutioning at high temperature. The results show that the temperature for the pseudo-dendritic γ′ precipitation is sensitive to the alloy composition in local area and that the relationship between the nucleation density (Ⅰ) and undercooling (△Tγ′) for the pseudo-dendritic γ′ precipitates is given by logarithmic expression: I(μm~2) = 2.5×10~(-3) exp(0. 11△T_(γ′)). The size of the pseudo-dendritic γ′precipitates is proportional to the direct aging time under small undercooling. The preferential growth direction of the pseudo-dendrite γ′precipiatates is <110> which is completely coherent with matrix. The formation mechanism for pseudo-dendrite γ′prencipitates involves both the diffusion and non- diffusion controlled. It intends to form nucleus symmetrically.Correspondent: ZHANG Jinghua, assoiate professor, Institute of Metal Research, Chinese Academy of Sci ences. Shenyang 110015
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    IN SITU TENSION OBSERVATION ON Ti-10V-2Fe-3Al ALLOY UNDER SEM AND TEM
    ZHU Weidou;GU Haicheng; GUO Yandong(Xi′an Jiaotong University)(Manuscript received 7 December; 1993; in revised form 14 March; 1994)
    Acta Metall Sin, 1994, 30 (10): 463-468. 
    Abstract   PDF (512KB) ( 630 )
    The in situ tension observations of SEM and TEM were carried out on specimens of a β solution treated Ti-10V-2Fe-3Al alloy with a sharp notch. Following tensile load increase the β→α″phase transformation and a″plate growth was clearly demonstrated.Owing to the SEM specimens were made of rather thin plates so the fracture was purely in ductile shear mode. The crack initiations took place on slip bands and the crack growth followed the re-nucleation and coalescence manner.DIC optical microscopy was used to identify the slip lines and a″plates.Correspondent: ZHU Weidou, associate professor, Department of Materials, Xi′an Jiaotong University, Xi′an710049
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    IN SITU OBSERVATION ON LOW CYCLIC FATIGUE IN TRIPHASE STEEL UNDER SEM
    HU Zhizhong; MA Mingriang; LIU Yanqing; LIU Jinghua (Xi′an Jiaotong University)(Manuscript received 22 December; 1993; in revised form 1 June; 1994)
    Acta Metall Sin, 1994, 30 (10): 469-476. 
    Abstract   PDF (695KB) ( 604 )
    The behaviour of austenite in the crack initiation and propagation of low cyclic fatigue for triphase steel (F-M-A) was observed in situ under SEM with fatigue loading stage. Results showed that the austenite in triphase steel during the crack initiation and early propasation of low cyclic fatigue may decrease the fatigue notch sensitivity and prolong the cyclic number of fatigue crack initiation, so as to flex the propagation path and to reduce the propagation rate of the cracks. At high strain fatigue stage, the strain-induced transformation of austenite may form the martensite, of which has the boundaries of low energy path for cracks propagation, the cracks may propagate more rapidly. Furthermore, an energy criterion was proposed, i, e., when the propagation work at crack tip is less than energy transformed from austenite into martensite, the fatigue resistance of steel may be improved by austenite, on the contrary, the crack initiation and propagation accelerated.Correspondent: HU Zhichong, senior engineer, Department of Materials Science and Engineering, Xi′an Jiaotong University, Xi′an 710049
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    FORMATION OF GRAIN BOUNDARY PRECIPITATE FREE ZONES IN 2091 Al-Li ALLOY AND ITS EFFECT ON STRESS CORROSION CRACKING
    LI Renshun; WANG Zuoyi(Harbin Institute of Technology)(Manuscript received 24 March; 1994; in revised form 30 May; 1994)
    Acta Metall Sin, 1994, 30 (10): 477-480. 
    Abstract   PDF (324KB) ( 650 )
    The stress corrosion cracking (SCC) susceptibility of 2091 Al-Li alloy was studied under tension at slow strain rate by quench aging in various media. TEM observation showed that the grain boundary precipitate free zones (PFZ) narrowed with accelerated quenching rate, yet gradually widened with the nucleation and growth of the grain boundary precipitated phase during aging. An interpretation seems to be given that the PFZ may be formed by a vacancy loss mechanism at initial stage of mechanism during sequent aging. The wider the PFZ is, the more susceptibel the alloy will be to SCC. Correspondent: Li Renshun, associate professor, Post Box No. 432, Harbin Institute of Technology, Harbin 150001
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