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ISSN 1005-0302
CN 21-1315/TG
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      28 January 1995, Volume 11 Issue 1 Previous Issue    Next Issue
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    Articles
    Structural and Magnetic Properties of Mechanically Alloyed Nd_(15)Fe_(70)T_(15)N_δ(T=V, Mo) Magnets
    Xinguo ZHAO; Zhidong ZHANG; Wei LIU; Qun WAN and Xaokai SUN(Institute of Metal Research, Chinese Academy f Sciences, Shenyang, 110015, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 1-4. 
    Abstract   HTML   PDF (373KB)
    Structural and magnetic properties of Nd15Fe70T15Nδ(T=V, Mo) alloys, made by mechanical alloying (MA) followed by heat-treatment and nitriding, have been investigated systematically.Effects of annealing temperature on the structure and magnetic properties of the materials were studied by means of X-ray diffraction, AC susceptibility and high field magnetization measurements. Under pure argon atmosphere, the optimum temperatures for the heat treatment are found to be 75 and 850℃ for Nd15Fe7015Nδ and Nd15Fe70Mo15Nδ respectively. Correspondingly, the following magnetic properties are achieved : (1) Nd15Fe70V15Nδ:Br=0.63 T,,HC=8.01kA/cm (10.1 kOe), (BH )max=50.3 kJ/m3 (6 32 MGOe), (2) Nd15Fe70Mo15Nδ :Br=0.42 T. iHc=5.6 kA/cm (7.4 kOe), (BH )max=26.6 kJ/m3 (3.34 MGOe)
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    Structural Dependence of Creep/Fatigue Behaviour of Single Crystal Ni-base Superalloy
    J. Zrnik and M.Hazlinger(Faculty of Metallurgy, Technical University, Kosice, Slovakia)M.Zitnansky(Material- Technological Faculty, Trnava, STU Bratislava,Slovakia)Zhongguang WANG(State Key Labratory for Faigue and Fracture of Materials, Institute of Meta
    J. Mater. Sci. Technol., 1995, 11 (1): 5-10. 
    Abstract   HTML   PDF (3638KB)
    The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation
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    In-situ Observation of Initiation and Propagation of Cleavage Microcrack in TiAl
    Kewei GAO; Qizhi CHEN; Wuyang CHU and Chimei Hsiao(Dept.of Materials Physics, University of Science and Technolgy Beijing, Beijing, 100083, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 11-14. 
    Abstract   HTML   PDF (1886KB)
    Nucleating and propagating of nancrack formed in dislocation free zone (DFZ) for the brittle TiAl alloy has been studied through in-situ tensile test in TEM and analyzed using microfracture mechanics. The resufts show that a lot of dislocations can be emitted from a crack tip when the applied stress intensity Kla i5 larger than the stress intensity for dislocatin emission Kle=1.4 M Pa·m1/2 and a dislocation free zone, which smetimes is a close zone, can form after reaching equilibrium. The DFZ is a elastic zone with large strain and then the stress in the DFZmight equal to the cohesive strength σth because the crack tip is still sharp. When Kla is larger than the stress intensity for nanocrack nucleation Kli =2.4 M Pa·m1/2, the stress within a certain range in the DFZ would equal to σth and then a nanocrack initiates in the DFZ or sometimes at the notch tip. The nanocrack formed in the DFZ is stable and can propagate a small distance in cleavage mode through multiplication and movement of dislocation in the plastic zone, during keeping constant displacement. Increasing Kla can make the crack stably propagate continuously or discontinuously and it means that the stre5s intensity for crack propagation, Klp, is larger than Kli. Therefre, Kle References | Related Articles | Metrics
    Rheological Behaviour for Polymer Melts and Concentrated Solutions Part Ⅰ:A New Multiple Reptation Model to Predict the Nonlinear Visco-elasticity with Nagai Chain Constraints in Entangled Polymer Melts
    Mingshi SONG and Sizhu WU(Dept. of Polymer Science, Beijing University of Chemical Technology Beijing, 100029, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 15-30. 
    Abstract   HTML   PDF (1402KB)
    An approach of stochastically statistical mechanics and a unified molecular theory of nonlinear viscoelasticity with constraints of Nagai chain entanglement for polymer melts have been proposed. A multimode model structure for a single polymer chain with n tail segments and N reversible entanglement sites on the test polymer chain is developed. Based on the above model structure and the mechanism of molecular flow by the dynamical reorganization of entanglement sites, the probability distribution function of the end-to-end vectr for a single polymer chain at entangled state and the viscoelastic free energy of deformation for polymer melts are calculated by using the method of the stochastically statistical mechanics. The four types of stress-strain relation and the memory function are derived from this thery. The above theoretical relations are verified by the experimentaf data for various polymer melts. These relations are found to be in good agreement with the experimental results
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    Dielectric Relaxations in Ferroelectric Copolymer VDF(73)/TrFE(27)
    Xingyuan ZHANG(Dept. of Materials Science and Engineering, University of Science and Technology of China, Hefei, 230026, China)Takeo Furukawa(Dept. of Chemistry, Science University of Tokyo, 162. Japan)
    J. Mater. Sci. Technol., 1995, 11 (1): 31-37. 
    Abstract   HTML   PDF (709KB)
    The characteristics of molecular mtin of ferroelectric copolymer VDF(73)/TrFE(27) have been investigated by means of dielectric relaxation. With the rise in crystallinity. the Curie point decreases and the dielectric constant increases in the region of ferroelectric-to-paraelectric phase transition. The frequency spectra of the coplymer below room temperature consist of lowfrequency component ascribed to the micro-Brownian motions of molecular segments in the noncrystalline regins and high-frequency cmponent associated with the local motions of smallscale segments. By using the fitting results with one or two Cole-Cole functions, and calculating with WLF equation and Arrhenius formula, the glass transition temperature and the activation energy of local relaxation are obtained. the distribution of relaxation time in the molten and ferroelectric phases is located at a same line, and complies with Arrhenius ruIe, which suggests that the elementary motions are of same type for molecular motions provided by the hightemperature process and the low-temperature local mode process
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    Realization of Superplastic State of Polycrystals under Grain-boundary Diffusion
    Yu.R.Kolobov and I.V.Ratochka(Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences,634055, Tomsk, Russia)
    J. Mater. Sci. Technol., 1995, 11 (1): 38-40. 
    Abstract   HTML   PDF (317KB)
    Creep behaviour of Mo and Fe polycrystals has been studied for a wide range of Strain rates in the presence of grain-boundary diffusion flux of Ni. The role of the impurity grain-boundary diffusion and grain-boundary migratin in the realization of the superplastic strain of metals under these conditions is examined
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    Characterization of Mixed Neodymium Lanthanum Heptamolybdate Crystals Grown by Gel Encapsulation Technique
    Sushma Bhat and P.N.Kotru(Dept. of Physics, University of Jammu, Jammu, India)
    J. Mater. Sci. Technol., 1995, 11 (1): 41-45. 
    Abstract   HTML   PDF (2580KB)
    Crystals of mixed NdLa heptamolybdates (max. size0.75×0.75×0.75 mm3) grown by silica gel technique were characterized using EDAX, IR, optical and scanning electron micrscopies.X-ray as well as electrn diffraction. The composition of the crystals was determined as (Nd1/2 La1/2 )2 Mo7O24·35H2O.The crystals exhibit varied morpholgies including square and octagonal platelets, cuboids, multifaceted crystal in coalesced and aggregated forms and spherulites.The XRD results indicate crystallinity of the grown material. Electron diffraction results suggest thermal instability of the material. IR results show the presence of peaks due to water and metal-oxygen bonds
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    Mechanical, Thermal, Morphological and Rheological Properties of Polypropylene/Ultrahigh Molecular Weight Polyethylene Blends
    Xiaodong WANG; Riguang JIN and Hangquan LI (Beijing University of Chemical Technology, Beijing, 100029, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 46-52. 
    Abstract   HTML   PDF (2434KB)
    In this study, the blends of polypropylene (PP) and ultrahigh molecular weight polyethylene (UHMWPE) were prepared by the four-and twin-screw extruders, and ethylene-propylene-diene monomer (EPDM), as the third component, was added to the binary blends. The mechanical.thermal, morphological and rheological properties of these two blends have been investigated.For the materials blended by the four-screw extruder, a 15 wt-% content of UHMWPE corresponds to a maximum lzod impact strength, and the miscibility enhancement effect of EPDM on PP/UHMWPE blends is very remarkable. Mechanical and thermal properties demonstrate that melt blending by the four-screw extruder is a better prcessing method for PP/UHMWPF blends than that by the twin-screw extruder. A co-continuous structure was observed in blends through TEM, and a novel "linear interpenetrating" toughening mechanism is proposed on the basis of this research work
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    X-ray Diffraction and Electrical Conductivity Studies on Ag-Cu-Se System
    S.N.Motafa and S.R.Selim(Chemistry Department, Al-Azhar University, Nasr City. Cairo. Egypt)F.M.Ismail(Inorganic Chemistry Department, National Research Center. Dokki. Cairo. Egypt)
    J. Mater. Sci. Technol., 1995, 11 (1): 53-55. 
    Abstract   HTML   PDF (264KB)
    A number of X-ray patterns and electrical conductivities of five different samples of Ag-Cu-Se system have been measured. These samples of Ag-Cu-Se system: (Ag1.188, Cu0.812)Se, (Ag,Cu)Se; (Ag0.9, Cu1.1 )Se, (Ag0.8, Cu1.2)Se and (Ag0.6, Cu1.4)Se were prepared under controlled conditions. Analysis of the experimental data shows that Frenkel defects are predominated in (Ag1.188, Cu0.812)Se and Schottky defects prevailing in the other samples. The activation energy values △E calculated from the linear behaviour of electrical conductivity a with temperature (0-90℃) reveal that the impurity content increases in the direction of (Ag,Cu)Se→(Ag0.8,Cu1.2 )Se
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    Effect of Solid/Liquid Interface Morphology on Microstructure and Segregation of DSX40M Superalloy
    Liling SUN; Qi WU Zhiya ZHANG and Zhuangqi HU(Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110015. China)
    J. Mater. Sci. Technol., 1995, 11 (1): 56-60. 
    Abstract   HTML   PDF (2662KB)
    The effect of solid/liquid intedece morphologies on the microstructure and segregation of a new type superalloy, DSX40M, was studied. It has been found that the primary arm spacing presents maximum value as the solid/liquid interface shape transforms from cellular to cellular-dendritic.As the alloy solidifies with a coarse dendritic interface, the solute segregation degree and the average size of the carbide reach the maximum values because of the widest mushy zone. A Zr-rich phase forms at this range. Within the solidificatin rate range of dendritic interface. the primary dendritic arm spacing and solute segregation decrease with the increasing of solidification rate and the Zr-rich phase disappears. It should be indicated that the change of the solid/liquid interface does nt vary the carbide type, but greatly affects the average size of the carbides.The quantitative results of the carbide size change in this alloy system with different solid/liquid interfaces is presented
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    Effect of Austenite Pre-deformation on Isothermal Martensite Transformation in an Fe-20.5Ni-4.8Mn Alloy
    Fuxing YIN; Jianxin ZHANG and Nanju GU(Hebei Institute of Technology, Tianjin, 300132, China)Tsukio Tadaki(Institute of Science and Industrial Research, Osaka University, Japan)Ken,ichi Shimizu(Kanazawa Institute of Technology, Ishigawa 921, Japan)
    J. Mater. Sci. Technol., 1995, 11 (1): 61-66. 
    Abstract   HTML   PDF (3461KB)
    With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deformation to austenite before isothermal holding. Under the condition without pre-deformation, the isothermal martensite products are lath martensite with {111}fhabit planes. Dislocations in austenite seem to contribute to nucleation of martensite, and in this nascent Stage austenite substructure has no obvious effect on martensite growth. The consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, morphology as well as substructure of martensite lath. The kinetics of isothermal martensite transformation is controlled by intedece dislocation determined nucleation of martensite in primary stage, but to a larger extent, by the austenite accommodation for the shape strain of martensite in the thickening Stage
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    Influence of Inhibitor Concentration on Corrosion Fatigue Crack Initiation and Propagation
    Zhengfu WANG; Jin LI; Jianqiu WANG and Wei KE(Corrosion Science Laboratory, Institute of Corrosion and Protection of Metals,Chinese Academy of Sciences, Shenyang, 110015, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 67-70. 
    Abstract   HTML   PDF (342KB)
    The paper reports the effect of0.01,0.1 and 1%NaNO2, a passive inhibitor, on corrosion fatigue (CF) crack initiation and propagation for a low strength structural steel A537 in 3.5%NaCl aqueous solution. The experimental results show that inhibitor increases the required cycles of CF crack initiation effectively, and this effect increases with increasing inhibitor concentration.However, there is nearly no effect of NaNO2 on CF crack propagation. The same CF crack propagation rate was found in all kinds of solutions. The results also indicate that the passive time in 1%NaNO2 solution during plastic deformation is much longer than cyclic time. NaNO2 passivates the specimen sudece and repairs passive film damaged by cyclic loading during the crack initiation. while the passsive film is not formed fully due to continuous plastic deformation at the crack tip during the CF crack propagation, which is much different from that in the stress corrosion cracking and general corrosion
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    Preparation of Ultrafine Si Powders from SiH_4 by Laser-induced Gas Phase Reaction
    Yali LI; Yong LIANG; Kesheng XIAO; Fen ZHENG and Zhuangqi HU(State Key Laboratory of Rapidly Solidified Nonequlibrium Alloys, Institute of Metal Research,Chinese Academy of Sciences, Shenyang, 110015, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 71-74. 
    Abstract   HTML   PDF (1262KB)
    High quality ultrafine Si powders have been synthesized from SiH4 by laser induced gas phase reaction. The powders prduced under different synthesis conditions have mean particle size of 10-120nm in diam. with narrow particle size distribution, and free of hard agglomerates.The powders are polycrystalline with the ratio of mean grain to particle diameter being between 0.3-0.7. The size of the powder increases with increasing laser power and reaction pressure,but decreases with increasing silane gas flow rate and the addition of Ar diluent. Grain sizes drop distinctly with the rise of the addition of Ar gas and laser power, but change little with the gas flow rate and reaction temperature. The formation of Si particles under different synthesis conditions is discussed
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    A Theoretical Study of the Pressure for Liquid Metal Infiltration of a Fiber Preform
    Sirong YU and Zhenming HE(Dept. of Metallic Materials Engineering, Jilin University of Technology, Changchun, 130025, China)
    J. Mater. Sci. Technol., 1995, 11 (1): 75-78. 
    Abstract   HTML   PDF (329KB)
    A theoretical model has been established for calculating the infiltration pressure of metal melt into the preform of ceramic fibers according to the basic principle of hydromechanics. There are three forces acting on the infiltration process in the model, i.e. viscous friction, capillary force, and gravity The effects of the volume fraction of fibers (Vf) and infiltrating depth on the infiltration pressure are discussed. The results show that the infiltration pressure increases with the increase of fiber volume fraction and infiltration depth. There is a linear relationship between infiltration pressure and infiltiation depth. The effect of gravity on the infiltration pressure can be ignored
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ISSN: 1005-0302
CN: 21-1315/TG
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