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ISSN 1005-0302
CN 21-1315/TG
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      28 May 1998, Volume 14 Issue 3 Previous Issue    Next Issue
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    Articles
    An SANS Study of Decomposition Kinetics in Amorphous Cu_(12.5)Ni_(10)Zr_(41)Ti_(14)Be_(22.5)
    Junming LIU(National Laboratory of Solid State Microstructures, Nanjing University and Center for Advanced Studies in Scienceand Technology of Microstructures, Nanjing 210093, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 193-199. 
    Abstract   HTML   PDF (2681KB)
    Phase decomposition in amorphous Cu12.5Ni10Zr411Ti14Be22.5 alloy as annealed in the super-cooled liquid range was studied by applying small angle neutron scattering (SANS). As annealed between 600 K and 700 K, the alloy was observed to decompose into two new amorphous phases,with the second phase precipitates embedded in the matrix of the first. Long time annealing of the alloy results in crystallization in addition to evolution of the decomposed microstructure.The kinetic diagram of the decomposition and crystallization for this alloy is given. The second phase precipitates have several nanometers in size and occupy a quite low volume fraction. The decomposition of the supercooled liquid in overall temperature range exhibits the features of spinodal reaction.
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    Influence of Crystal Orientation on the Morphology of a Single Crystal Superalloy during Directional Solidification
    Guo HE; Jianguo LI; Xemin MAO and Hengzhi FU( State Key Laboratory for Advanced Met-als and Materials, University of Science and TechnologyBeijing, Beijing 100083, China)(State Key Laboratory of Solidification Processing, Northwestern Polytechnical Univer
    J. Mater. Sci. Technol., 1998, 14 (3): 200-204. 
    Abstract   HTML   PDF (2472KB)
    The solid-liquid(S/L) intedecial morphology of a single crystal superalloy DD8 has been in-vestigated. The evolutive behavior of cellular morphology with tilted preferred crystallographic orientation near cell-dendrite transition was dynamically observed, and the efFect of crystallo-graphic orientation on primary dendritic arm spacing has been examined. The experimental results show that for planar and cellular morphology no any S/L interfacial anisotropy exists,but near cell-dendrite transition, the S/L intedecial anisotropy appears and gives rise to the cellular crystal fingers tilted from thermal flow direction to preferred crystallographic orientation.The crystal fingers with their preferred orientation parallel to DS growth direction are more stable than that with tilted orientation. For the tilted fingers, the sudece on the side facing DS growth direction is less stable than that on the reverse side, the different stability on the two sides will lead to forming unsymmetrical dendritical microstructure. With the increase of tilted angle of preferred crystallographic orientation, the primary dendrite arm spacing decreases.
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    Studies of Structure Evolution of Nanostructured Hf_(11)Ni_(89) Alloy
    Zhenfu DONG and Lianmao PENG(Beijing Lab. of Electron Microscopy, Institute of Physics and Center for Condensed Matter Physics,Chinese Academy of Sciences, P.O.Box 2724, Beijing 100080, China)Ke LU and Zhuangqi HU(State Key Lab. for RSA, Institute of Meta
    J. Mater. Sci. Technol., 1998, 14 (3): 205-210. 
    Abstract   HTML   PDF (2366KB)
    A nanostructured Hf11Ni89 ribbon sample was prepared by melt-spinning. It was found that the as-quenched sample is composed of a major HfNi5 compound nanophase and an interfacial magnetic Ni(Hf) solid solution phase. The structure evolution of the sample was studied by using X-ray difFraction (XRD), transmission electron microscopy (TEM), difFerential scanning calorimetry (DSC), resistivity and magnetothermal analysis. Upon heating, a second precipitation process of the Ni(Hf) phase prior to grain growth wa5 detected by means of both structural analysis and physical property measurements. The measurement results are discussed based on the relationship between microstructure and physical properties.
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    Cyclic Saturation Dislocation Pattern Observation in the Vicinity of Grain Boundaries by Electron Channeling Contrast Technique
    Zhefeng ZHANG; Xiaowu LI Huihe SU and Zhongguang WANG
    J. Mater. Sci. Technol., 1998, 14 (3): 211-214. 
    Abstract   HTML   PDF (1600KB)
    State Key Laboratory for Fatigue and Fracture of Materials, Institute of Metal Research, Chinese Academy of Sciences,Shenyang, 110015, China)Abstract:The cyclic saturation dislocation patterns within grains and in the vicinity of low-angle grain boundaries in fatigued copper crystal were successfully observed by electron channeling contrast technique in SEM. The results show that the dislocation patterns within grains consisted of typical two-phase structure, i.e. persistent slip bands (PSB) and veins. With increasing plastic strain amplitude (γp1 ≥1.7×10-3), large amount of PSBs and regufar dislocation walls were observed.The dislocation walls and PSBs could cross through the low-angle grain boundaries continuously except that the dislocation-free zone (DFZs) appeared at some local regions. Combining with the cyclic stress-strain response and dislocation patterns, the effect of low-angle grain boundaries on cyclic deformation behavior was discussed.
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    Unusual Behaviour of Dislocation Velocity Exponent in Dislocation Multiplication Model
    Xaowei WANG(International Centre for Materials Physics, Institute of Metal Research, Chinese Academy of Sciences,Shenyang 110015, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 215-218. 
    Abstract   HTML   PDF (390KB)
    The chaotic behavior of dislocation multiplication process is investigated. The change of Lya-punov exponent which is used to determine the stability of quasi-periodic and chaotic behavior as well as that of equilibrium points and periodic solution is reported using an iteration model of dislocation multiplication. An unusual behavior of Lyapunov exponent and Feigenbaum ex-ponent which respond to the geometric convergence of orbit from bifurcation to chaos is shown by dislocation velocity exponent m and there is a distinction on the tendency of convergence for the dislocation multipIication model when it is compared with togistic map. lt is reasonable for the difference to be analyzed from the materials viewpoint.
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    High Temperature Creep and Fracture Behavior of a Directionally Solidified Ni-base Superalloy
    Chao YUAN; Jianting GUO and Shuhe WANG(Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China)Hongcai YANG(Dept. of Materials Science and Engineering, Northeastern University, Shenyang 110006, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 219-225. 
    Abstract   HTML   PDF (3511KB)
    The tensile creep-fracture properties of DZ17G. a directionally solidified superalloy, were inves-tigated at 830~ 900℃. The results show that all of the creep curves exhibit negligible primary creep, relatively little steady-state creep and dominant tertiary creep stage. The higher apparent activation energy for creep (540 kJ/mol ) suggests that the creep is controlled by Orowan bowing process. A large ratio of the fracture time to the onset time of tertiary creep is the consequence of microstructure change, i.e., γ particles oriented coarsening parallel to the applied stress axis.The creep fracture data follow the Monkman-Grant relationship. The transgranuIar fracture mechanism proposed on the basis of the metallographic examinations is the linkage of the creep cracks which initiate at the discontinuities with the microstructure (such as the cast porosity,and the carbide/matrix intedece) and also at the specimen surface, that propagate along the γ/γ intedece with perpendicular to the applied stress axis, and the process of crack propagation can be described by the Tien model.
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    Effects of Long-term Creep at Elevated Temperatures on Rupture Ductility in 9Cr-1Mo-V-Nb-N Steel
    Lihui ZHU; Qinxin ZHAO; Haicheng GU and Yansun LUSchool of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 226-230. 
    Abstract   HTML   PDF (2202KB)
    Besides the creep strength, creep ductility has also been recognized as an important material parameter, since low ductility is often associated with notch sensitivity and concomitant prema-ture failure, especially brittle fracture. Creep rupture data of 9Cr-1Mo-V-Nb-N show that the creep ductility decreases with decreasing stress at constant temperatures or with decreasing tem-perature at constant stresses. SEM and TEM were used to investigate the mechanism of creep brittleness. The results indicate that the decrease of rupture ductility after long-term creep is related to the decrease of mobile dislocation density, the coarsening and coalescence of carbides and the decrease of shear lip size.
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    Optical and Structural Properties of In_(0.52)Al_(0.48)As/InP Structures Grown at Very High Arsenic Overpressures by Molecular Beam Epitaxy
    S.F. Yoon(School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue,Singapore 639798, Rep. of Singapore
    J. Mater. Sci. Technol., 1998, 14 (3): 231-235. 
    Abstract   HTML   PDF (594KB)
    Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) shows a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 result in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the lnAs-like and AlAs-like longitudinal-optic (LO)phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectra taken at increasing temperatures show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements show a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.
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    Preparation and Characterization of Some Ferrites from CuO-ZnO-Fe_2O_3 Mixtures
    A.A.Hanna; H.I Saleh and M.Sh.Khalil(Inorg. Chem. Dept., National Research Centre, Dokki, Cairo, Egypt)
    J. Mater. Sci. Technol., 1998, 14 (3): 236-240. 
    Abstract   HTML   PDF (1722KB)
    The ferrites of Cuo-ZnO-Fe2o3 solid solution series near the molar ratio of ZnxCu1-x were prepared by direct heating of their coprecipitated hydroxides using NH4OH as precipitating agent where x=0.0, 0.2, 0.5, 0.8 and 1.0. Additional amounts of Cu and Zn sulphates were added to compensate the loss during the coprecipitation of the hydroxides. The ferritized samples were characterized by chemical analysis, XRD. DTA, TGA and SEM. XRD of both Zn0.2Cu0.8Fe2O4 and Zn0.5Cu0.5 Fe2O4 that indicates the formation of a heterogeneous ferrite material of ZnFe2O4 and CuFe2O4 mixed with variable amounts of α-Fe2O3. Zn and Cu ferrites were observed only in Zn0.8Cu0.2Fe2O4.From TGA-time relation, the activation energy of the different transformation phases were calculated. It is found that, the activation energy of ZnFe2O4 is slightly equal to 3/2 of that for CuFe2O4. Dielectric measurements show that the electrical behaviour depends on the ordering and disordering of the phases.
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    Macroscopic Studies on the Properties of the Anodic Oxide Films on Titanium
    G.A.EL-Mahdy (Chemistry Dept., Faculty of Science, Helwan University, Helwan, Cairo, EgyptS-S.MahmoudChemistry Dept., University College for Women, Ain-Shams University, Helopolis, Cairo, Egypt)
    J. Mater. Sci. Technol., 1998, 14 (3): 241-246. 
    Abstract   HTML   PDF (636KB)
    The effect of fluoride ions on the formation and dissolution behaviour of anodic oxide films on Ti has been investigated in acidic fluoride media (pH=1) using impedance and galvanostatic techniques. A5 the fluoride ion concentration and temperature increase the rate of oxide film formation decreases while the dissolution process increases. oxide film formed at high tem-perature and formation voltage was found to contain more defect sites in the film than that formed at a lower one. Activation energies are calculated during the oxide film formation and dissolution and found to be 20.76 and 28.72 kJ/mol, respectively. Formation rate and reciprocal capacitance data are reported as a function of polarizing current density. Values are recorded for the electrolytic parameters A and B. Potentiostatic curves are derived from the galvanostatic results.
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    AC Conductivity of (As_2Te_3)_(100-x)Ge_x Bulk Glassy System
    A-Abdel-All(Physics Dept., Faculty of Science, Helwan University, Cairo, Egypt)
    J. Mater. Sci. Technol., 1998, 14 (3): 247-250. 
    Abstract   HTML   PDF (394KB)
    The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ranging from 3O to 160℃. lt was found that at a fixed temperature, where n <1 and decreases with temperature. The complex impedence Z was measured over the same frequency and temperature ranges. All samples give a semicircle arc originating at the origin point. This indicates that each composition can be described only by one resistance R and one capacity C, both parallelly combined. The centre below the real axis indicates the relaxation behaviour of the system. The activation energies for conduction were calculated.
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    Mobility of Various Intervariant Interfaces in 18R Martensite in a Cu-Zn-Al Alloy Part Ⅰ: In-situ Observations
    Jianxin ZHANG; Wei CAI; Yufeng ZHENG and Liancheng ZHAO(School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 251-254. 
    Abstract   HTML   PDF (3630KB)
    The motion of intervariant intedeces under the action of applied stress in the internally faulted 18R martensite in a Cu-Zn-Al shape memory alloy has been studied. Transmission electron microscopy in situ observations show that the interfaces between 24 martensite variants have different reaction to applied stress. The A/C type and A/B type interfaces have good mobil-ity, the A/D type interface has bad mobiIity, and the different-group-intervariant interfaces are basically immobile.
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    Microstructure and Mechanical Property of in-situ Al-Cu/TiC Composites
    Erlin ZHANG; Songyan ZENG; Bo YANG and Qingchun LI(School of Material Science and Engineering, Harbin Institute of Technology Harbin 150001, China)Mingzhen MA(Jiamusi University, Jiamusi 154002, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 255-258. 
    Abstract   HTML   PDF (2689KB)
    An approach named direct reaction synthesis (DRS) has been developed to fabricate particulate composites with an extremely fine reinforcement size. ID situ Al matrix composites were fabri-cated by DRS. Extensive analysis of the composites microstructure using SEM and TEM identify that the reinforcement formed during the DRS process is Ti carbide (TiC) particle, generally less than 1.0 μm. The reacted, semisolid extruded samples exhibit a homogeneous distribution of fine TiC particles in Al-Cu matrix, Mechanical property evaluation of the composites has revealed a very high tensile strength relative to the matrix alloy. Fractographic analysis indicates ductile failure although the ductility and strength are limited by the presence of coarse titanium aluminides (Al3Ti).
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    Aging Characteristics, Stress Corrosion Behaviour and Role of Mg Segregation at Grain Boundary in 7175High-strength Al Alloy
    Renguo SONG; Ping GENG; Meiguang ZENG and Baojin ZHANG( Dept. of Materials Physics, Universityof Science and Technology Beijing, Beijing 1ooo83, China)(Dept. of Materials Science, Science College, Northeastern University Shenyang 110006, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 259-264. 
    Abstract   HTML   PDF (605KB)
    The aging characteristics, stress corrosion behaviour and chemical composition of grain boundary in 7175 high-strength Al alloy during long term aging process have been investigated by hardness measurement, constant elongation rate testing (CERT) and energy spectroscopy analysis. The results indicate that double peaks in aged state feature the hardness and strength of 7175 Al alloy Although the intensity of double peaks is almost equal, the stress corrosion resistance in the second peak-aged state is better than that of the first peak-aged state. The effects of Mg segregation on the binding energy of grain boundary have been calculated by using free electron theory developed by the authors. The results show that Mg segregation plays a significant role in controlling stress corrosion susceptibility which is consistent with the experimental results.
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    Ballistic Penetration of Dyneema Fiber Laminate
    Zuoguang ZHANG; Shiguang; SHEN Huancheng SONG and Daxing ZHANG(Dept. of Materials Science and Engineering, Beijing University of Aeronautics and Astronaustics, Beijing 100083, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 265-268. 
    Abstract   HTML   PDF (1137KB)
    UHMWPE fiber (Dyneema) reinforced composites are an important class of materials for armors.These materials provide superior ballistic performance to the armor, such as the military armor systems requiring a reduction in back-armor effects or a substrate for hardened facings of steet or ceramic. The reported work characterized the ballistic impact and mechanical performance of Dyneema fiber in composite laminates. The capability of the laminate to absorb ballistic impact energy was influenced by the impact velocity and the laminate areal density. Two kinds of penetration were compared and a two-step model for the penetration was proposed.
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    Reactive Magnetron Sputtering of CN_x Thin Films on β-Si_3N_4 Substrates
    WT.Zheng; N-Hellgren and J.-E.Sundgren( Dept. of Materials Science, Jilin Univer-sity Changchun 13oo23, China)(Dept. of Physics, Linkoping University, S-581 83 Linkoping, Sweden)
    J. Mater. Sci. Technol., 1998, 14 (3): 269-272. 
    Abstract   HTML   PDF (1127KB)
    Carbon nitride CN. thin films have been deposited on polycrystalline β-Si3N4 substrates by un-balanced magnetron sputtering in a nitrogen discharge. Both the film deposition rate and the nitrogen concentration decrease with substrate temperature increase in the range of 100~400℃The maximum of nitrogen content is 40 at. pct. Raman spectroscopy and atomic force mi-croscopy were used to characterize the bonding, microstructure and surface roughness of the films. Nanoindentation experiments exhibit a higher hardness of 70 GPa and an extremely elas-tic recovery of 85% at higher substrate temperature.
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    Nucleation and Blunting of Nanocracks in Brass
    Biao GU; Wuynag CHU; Lijie QIAO; Qizhi CHEN and Chimei Hsiao(Dept. of Material Physics, University of Science and Technology Beijing, Beijing 100083, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 273-276. 
    Abstract   HTML   PDF (3014KB)
    In situ tensile test of brass foil specimens in TEM shows that many dislocations were emitted from a loaded crack tip and a dislocation free zone (DFZ) was formed under condition of constant displacement. The DFZ is an elastic zone, where the stress may equal to the cohesive strength th when the applied stress is high enough. As a result, nanocracks would initiate discontinuously in the DFZ or, sometimes, at a blunted-crack tip. As soon as the nanocrack nucleated, it quickly blunts into a void, which results in ductile fracture.
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    Factors Affecting Terminal Solid Solubility in Alloy Systems
    Jingkang GUO; Hang SU; Chonghe LI and Nianvi CHEN(Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 277-280. 
    Abstract   HTML   PDF (314KB)
    Pattern recognition method is applied to investigation of the factors affecting the terminal solid solubility in binary alloy systems. lt has been found that the atomic volume, the valence eltectron number and the melting point of the solute etements exhibit good correlation with the terminal solid solubility.
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    Structural Evolution of an FeMoSiB Alloy during Ball Milling
    Faqiang GUO and Ke LU(State Key Lab. for RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China)
    J. Mater. Sci. Technol., 1998, 14 (3): 281-285. 
    Abstract   HTML   PDF (1511KB)
    Ball milling induced microstructure evolution in an FeMoSiB alloy with three kinds of different phase constitutions (bcc Fe solid solution and various borides) was investigated by means of X-ray diffraction and transmission electron microscopy. Experimental evidences indicate that a same final product of bcc Fe solid solution was formed upon miling for all samples. During the transformation, the XRD peaks of Fe phase shift to lower diffraction angIes; and those of borides disappear in turn, first the metastable Fe3B and Fe23B6 and then the stable Fe2B. The observed structure evolution might originate from the transformation of ordered Fe2B phase into disordered Fe solid solution.
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    Effective Elastic Moduli of Ceramics with Pores
    Fenghui WANG and Wenxuan GOU(Dept. of Engineering Mechanics, Northwestern Polytechnical University, Xi'an 710072, China)Xiulin ZHENG(Dept. of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China)Minxu LU(Xi'an Tubu
    J. Mater. Sci. Technol., 1998, 14 (3): 286-288. 
    Abstract   HTML   PDF (225KB)
    A contribution is given to the theoretical research on the stiffness of ceramic materials, under the approximation of the average stress field, the relation E = E0(1 -p)/(1+ 2.5p) is derived to describe the dependence of the modulus of etasticity on porosity. The prediction of this model is consistent with the experimental data from several ceramics such as reacting sintered Si3N4,MgO and MgAl2O3.
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ISSN: 1005-0302
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