Strted in 1985 Monthly
ISSN 1005-0302
CN 21-1315/TG
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      28 September 1999, Volume 15 Issue 05 Previous Issue    Next Issue
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    Research Articles
    Control of Fracture Behavior of Carbon Fiber/Pitch-based Carbon Matrix Composites with Microspace Modification Concept
    Shiushichi Kimura, Kouichi Yasuda, Yohtaro Matsuo, Aira Hotta
    J. Mater. Sci. Technol., 1999, 15 (05): 393-399. 
    Theoretical consideration was conducted on a relation between pore diameter and interfacial area between pores and fibers when pores uniformly distribute in C/C composites. It was shown that bonding at the fiber/matrix interface apparently decreased with decreasing a pore diameter, and consequently a new idea of microspace modification concept was proposed for controlling fracture behavior of C/C composites. Four types of C/C composites with various pore structures were fabricated by hot-pressing, and their fracture behavior was investigated by three point bending tests. The fracture behavior of the C/C composites was changed from brittle one to pseudo ductile one with decreasing the pore diameter. This result supported the validity of the microspace modification concept proposed in this paper.
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    Experimental Study on Deoxidization of Barium and Barium Alloy
    Yufang SHI, Boping CHEN, Jie FU, Tarek El Gammal
    J. Mater. Sci. Technol., 1999, 15 (05): 400-404. 
    Based on the review of latest papers related to the application of barium alloy, the deoxidization effects of barium and barium alloy, and the dynamic characteristics of molten bath have been systematically studied by means of the convection free bath, natural convection bath, air and vacuum induction melting experiments. It was found that both the total oxygen content and soluble oxygen content in molten bath decreased rapidly. The results obtained provided practical and theoretical basis for further synthetic applications of barium alloy in metallurgical industry.
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    Structural Evolution of Fullerene during Mechanical Milling
    Z.G.Liu, H.Ohi, K.Tsuchiya, M.Umemoto, K.Masuyama
    J. Mater. Sci. Technol., 1999, 15 (05): 405-409. 
    Mechanical milling of fullerene C60(C70) was investigated to understand the structural evolution. Mechanical milling could not destroy the molecular structure of C60(C70), while the long range periodicity of the fcc crystalline structure was easily damaged. Longer milling time could result in the formation of C60(C70) polymer, including C60 dimer.
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    On the Methods of Beam Direction and Misorientation Angle/Axis Determination by Systematic Tilt
    Yonghua RONG, Gang HE, Shipu CHEN, Genxiang HU, Ming GAO, Robert P.WEI
    J. Mater. Sci. Technol., 1999, 15 (05): 410-414. 
    The methods for determining electron beam direction and misorientation angle/axis of grain boundaries are described in this paper. The present methods are based on a series of diffraction spot patterns obtained by systematic tilt of the crystal, combined with simple mathematical calculations. Instead of the use of Kikuchi patterns, the limitations resulting from the visibility or sharpness of Kikuchi lines and the number of Kikuchi pole(s) existed are avoided and a sufficient accuracy of determination has been achieved.
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    Effects of Zr on Microstructure and Short-Term Strength in GH586
    Shishu XIE, Tieli WANG, Junying LU, Hongcai YANG, Guangpu ZHAO
    J. Mater. Sci. Technol., 1999, 15 (05): 415-418. 
    0.020, 0.045 and 0.075 wt pct Zr were added to a Ni-base superalloy GH586 to investigate their effects on the microstructure and the short-term strengths at 850℃. The results showed that proper Zr addition could improve the alloy tensile strength at 850℃and short-term rupture life at 850℃, 580 MPa. Zr exists in both γ' phase and γ matrix, which caused Zr to distribute in grain instead of segregating in grain boundaries, therefore increased both of their lattice parameters but decreased the mismatch between them. Meanwhile, it also increased the amount of grain-boundary carbides and decreased their size markedly. These contributed to the improvement of short-term rupture life. However, further addition of Zr resulted in forming Zr4C2S2, a plate-like stable sulphurocarbides in grain boundaries, which decreased short-term strength at high temperature, and led to a worse hot workability. According to the experimental results, the optimum content of Zr should be 0.020 wt pct.
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    Step Sintering of Microwave Heating and Microwave Plasma Heating for Alumina Ceramics
    Jinsong ZHANG, Lihua CAO, Yongjin YANG, Yunxiang DIAO, Xuexuan SHEN
    J. Mater. Sci. Technol., 1999, 15 (05): 419-422. 
    The invention of microwave induced plasma during microwave heating makes it possible to confine plasma inside a crucible, in the pressure range of 1.33 Pa to 0.5 MPa, and above 900℃. In this study, the step sintering of microwave heating and microwave plasma heating (SSMP) was proposed. In this process, microwave heating and plasma heating was ingeniously combined in one chamber, and vacuum was unnecessary for microwave-induced plasma. In the first step, the microwave energy directly heated alumina ceramics to a given temperature, above which microwave will mainly ionize the gas and sustain a plasma. Then the plasma further heated alumina ceramics to the final temperature to finish sintering. Maintaining the advantages of microwave heating and plasma heating, this step sintering approach will overcome the limitation of both processes for processing ceramics, and it will be suitable for sintering all kinds of ceramics in principle.
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    Phase Structure Change of Mo-Si System during Mechanical Alloying
    Shaojun LIU, Xuanhui QU, Zhijiang LIU, Baiyun HUANG
    J. Mater. Sci. Technol., 1999, 15 (05): 423-426. 
    The structure of Mo-15.16 Si, Mo-30 Si and Mo-36.3 Si (wt pct) elemental powder mixture during mechanical alloying was studied using electron microscopy and X-ray diffraction. It had been found that, in all the systems under study, silicon disappeared initially during mechanical alloying (MA). In the Mo-Si systems all products were in form of amorphous state after long time milling, but there were different intermediate products. MoSi2 and Mo5Si3 intermetallic compounds in the Mo-30Si and Mo-36.3Si (wt pct) were directly synthesized from elements through inter-diffussion process. The high density of defects and interface of nano-crystallines induced by ball milling would promote the reaction process. Only in the Mo-15.16Si (wt pct) system was Mo(Si) supersaturated solid solution formed as an intermediate product. Schematic free-energy diagram of Mo-Si system based on the thermodynamics was used to analyze the difference among the intermediate state products.
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    Preliminary Investigation of NiAl-TiB2 Composite Prepared by Reaction Milling
    Lanzhang ZHOU, Jianting GUO
    J. Mater. Sci. Technol., 1999, 15 (05): 427-430. 
    Reaction-milled NiAl-TiB2 composite was fabricated by mechanical alloying elemental powders and hot pressing. TiB2 particles are distributed mostly in grain boundaries of the matrix. The compressive strain to failure of the composite at RT is about twice that of cast NiAl. The compressive yield stress at high temperatures is about 4.5 times higher than that of extruded NiAl, and is also much stronger than XD NiAl-TiB2 composites. Deformation behavior between 1000-1100℃ with different strain rates has been investigated.
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    Phosphogypsum: Part I: Mineralogical, Thermogravimetric, Chemical and Infrared Characterization
    A.A.Hanna, A.I.M.Akarish, S.M.Ahmed
    J. Mater. Sci. Technol., 1999, 15 (05): 431-434. 
    Phosphogypsum (PG) derived from the dissolution of phosphate ore in H2SO4 has been characterized by using chemical and thermogravimetric analyses, X-ray diffraction and infrared spectrum to give an idea about the future utilization of this waste material. The PG under the investigation was free from the radioactive elements and Cd and contained about 141×10-6 rare earth elements in total, which favors the utilization of this material. PG was formed mainly of gypsum, little anhydrite and quartz and rare kaolinite. It exhibited two large endothermic peaks corresponding to the dehydration of the sample and a small one which may be attributed to the liberation of the residual water that may be found in the soluble anhydrite. Also, an exothermic peak was observed which may be related to the transformation of soluble (γ-anhydrite) to insoluble β-anhydrite. PG exhibited the same absorption bands as that observed for chemical CaSO4.2H2O and natural gypsum samples besides the appearance of a weak band at 840 cm-1 which characterizes the vibration of H2PO4- group.
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    A Model of Dynamic Recrystallization in Alloys during High Strain Plastic Deformation
    Qiang LI, Yongbo XU, Zuhan LAI, Letian SHEN, Yilong BAI
    J. Mater. Sci. Technol., 1999, 15 (05): 435-438. 
    Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization. Based on dislocation dynamics and grain orientation change enhanced by plastic deformation, a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization.
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    Phase Diagram Prediction of the Al2O3-SiO2-La2O3 System
    Lin LI, Zhujun TANG, Weiying SUN, Peiling WANG
    J. Mater. Sci. Technol., 1999, 15 (05): 439-443. 
    Rare earth oxide systems Al2O3-La2O3 and SiO2-La2O3 were thermodynamically assessed and optimized with the substitution model. The obtained model parameters and Gibbs free energy of line compounds and pure components were applied to the prediction of the liquidus surface and isothermal sections of Al2O3-SiO2-La2O3 system.
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    Internal Oxidation of Cu-Al Alloy
    Jianjun WU, Yun ZHANG, Yutian SHEN, Guobin LI, Tingquan LEI
    J. Mater. Sci. Technol., 1999, 15 (05): 444-448. 
    The thermodynamics and kinetics of the internal oxidation in dilute Cu-Al alloy are investigated. The internal oxidation of copper alloy containing 0.2-1.2 wt pct Al is studied in the temperature range from 1073 K to 1273 K. A related equilibrium diagram is drawn. A mathematic model of oxidation layer depth is developed on the base of the experimental results. The experiments and investigation show that the formation rate of the internal oxidation layer is mainly controlled by the diffusion of O in matrix, the O concentration on the surface and the Al concentration in the alloy.
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    Valence Change and Luminescence of Divalent Samarium in Strontium Borates
    Qinghua ZENG, Zhiwu PEI, Shubing WANG, Qing SU, Shaozhe LU
    J. Mater. Sci. Technol., 1999, 15 (05): 449-452. 
    The valence change of samarium from trivalent to divalent state in strontium borates (SrB6O10) prepared in air was observed. The high resolution spectra of Sm2+ in matrix were studied between 10 K and 300 K. The results showed that three crystallographic sites for Sm2+ were available in the host. Energy transfer among these sites was possible. The vibronic transition of 5D0→7F0 of Sm2+ was studied at room temperature and the Huang-Rhys factor S was calculated. Due to the thermal population, 5D1→F0 transition at room temperature was observed.
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    Structural and Magnetic Properties of MnO-P2O5-PbO Glasses
    I.Ardelean, M.Peteanu, O.Cozar, V.Simon, V.Mih, G.Botezan
    J. Mater. Sci. Technol., 1999, 15 (05): 453-456. 
    The xMnO(100-x)[2P2O5•PbO] glasses were prepared with MnO concentration being in the range of 0≤x≤50 mole fraction and were investigated by EPR spectroscopy and magnetic susceptibility measurements. Octahedral symmetric sites tetragonally distorted were detected for x≤5 mole fraction MnO. Only Mn2+ ions were identified in these glasses, involved in dipole-dipole interactions.
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    Effect of Differential Thermal Expansion Coefficient on Stresses Generated in Coating
    H.M.Soliman, A.F.Waheed
    J. Mater. Sci. Technol., 1999, 15 (05): 457-462. 
    Two different spraying powders [81FVNS and 80% (443)+20% (105)] were plasma sprayed on two types of substrates (AISI 316 and Ti) in order to verify the effect of differential thermal expansion coefficient (DTEC) between coating and substrate on the final residual stresses generated in the coating. Modulus of elasticity (E) was evaluated for the substrates and coatings (as a composite beam). Free-standing coatings were used to measure the thermal expansion coefficient, as a function of temperature, of the actual coatings with all defects, impurities and typical lamella structure. The results show that the residual stresses seems to be less dependent on the linear thermal expansion coefficients mismatching between substrate and coating, reflecting the importance of the other sources of stresses. i.e. quenching or deposition stresses induced during spraying. The suitable heat treatment condition of the coated samples may release some or most of the residual stresses. However in some cases the sign of the stress was completely changed as a result of neglecting the quenching stresses.
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    Grain Boundary-induced Shielding of Ni-base Single Crystals: Experimental and Analytical Study
    Zhufeng YUE, Zhenzhou Lü, Deqiang WU
    J. Mater. Sci. Technol., 1999, 15 (05): 463-468. 
    Fracture behavior was studied for Ni-base single crystals and Ni-base bicrystals. The singlecrystals were machined from the bicrystal specimens to ensure that the single crystal samples had the same properties as those of the grains in the bicrystals. Using the three-point bend specimens, the fracture toughness Kc of single crystals and grain boundaries was measured, respectively. The two toughness values were little dependent on the ratio of the crack length to the height of the specimens. The grain boundary-induced shielding effect of fracture toughness was found in the grain-cracked bicrystals with normal front grain boundaries. The toughness varied with the distance between the crack tip and grain boundary. With the help of SEM analyses and numerical calculations, the mechanisms for the grain boundary-induced shielding are revealed. It is the grain boundary-induced redistribution of stresses and strains near the crack tip that induces the grain boundary-induced shielding. And the strain energy density criterion can be applied to the fracture of bicrystals. Agreement with experiments is good.
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    Precipitation of α Phase in the Massive and Feathery Structures in TiAl Alloys during Aging in the Single α Field
    Weijun ZHANG, Guoliang CHEN
    J. Mater. Sci. Technol., 1999, 15 (05): 469-472. 
    Precipitation of α-phase in massive and feathery microstructures was studied during aging in the single α field. It was found that the α-phase mainly precipitated along the γ-plate interfaces as laths in the feathery structure, while it nucleated at various sites in the massive structure in the form of particles and dominantly as plates. Precipitation of α-plates in the massive structure occurred by the diffusional ledge mechanism. The γm→α reaction proceeded by the growth of previously nucleated α-precipitates, and chiefly by the development of new α-plates.
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    Preparation and Characterization of Ni-Ferrite Coating on Carbon Steel Coupons
    M.P.Srinivasan, Santanu Bera, S.V.Narasimhan
    J. Mater. Sci. Technol., 1999, 15 (05): 473-477. 
    The effect of the presence of Ni in solution as Ni-EDTA complex in lithiated water at room temperature and pH 10.5 on the formation of ferrite coating on carbon steel surface was studied in an autoclave at 523 K for 12 days at different Ni concentrations with varying amounts of free EDTA. The Ni-ferrite coating was characterized by XRD, SIMS and XPS and also bulk chemical analysis by AAS and UV-visible spectrophotometer. The chemical composition of Ni-ferrite coating showed variation with depth across solution-oxide interface to oxide-metal interface. The content of Ni in the oxide coating on the surface near solution-oxide interface was found to be higher than the average Ni content estimated by analysis after descaling the coating.
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    Thermodynamics of Ordering-Disordering Transformation in Cu-Zn Alloy System
    Liuding WANG, Changle CHEN, Yimin SHI, Mokuang KANG, Bangjie JI
    J. Mater. Sci. Technol., 1999, 15 (05): 478-479. 
    The α and β phases in Cu-Zn alloy system were regarded as regular solutions at elevated temperature, the results calculated from the experimental data have showed that the value of the interaction parameter of components Cu and Zn in the α phase ECuZnα varied obviously with decreasing component Zn. Substituting the function relation between ECuZnα and XZn obtained through curve-fitting into expression of free-energy variation of the system, the calculated martensitic transformation temperature Ms was in good agreement with experimental curve, so as to have more comprehensive information for fully making use of binary Cu-base functional materials.
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    Experimental Observation of Cubic C3N4 Compound in Carbon Nitride Thin Films
    Furen XIAO, Dongli YU, Yongjun TIAN, Julong HE, Dongchun LI, Wenkui WANG
    J. Mater. Sci. Technol., 1999, 15 (05): 480-482. 
    Cubic C3N4 compoundin the C-N thin films on Si and NaCl substrates was prepared by ion beamsputtering of a pure graphite target with discharge gas of pure N2. X-ray photoelectron spectroscopy indicated that nitrogen atoms combinedwith sp2- and sp3- coordinated C atoms in the film, respectively. X-ray diffraction, selected area electron diffraction and high-resolution electron microscopy were used to identify the cubic C3N4 phase. The results reconfirm the ab initio calculations on metastable structure in C-N compounds.
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    Effects of Sn+ Ion Implantation on the Thermoelectric Properties of n-type Lead Telluride
    Qiang SHEN, Lianmeng ZHANG, Junguo LI, Rong TU, Lidong CHEN
    J. Mater. Sci. Technol., 1999, 15 (05): 483-485. 
    The n-type PbTe doped with 0.05 mol fraction PbI2 was hot-pressed, and the sintered samples were implanted by Sn+ ions at 200 keV with doses of 6×1016 and 1×1017 ions/cm2. The effect of Sn+ implantation on thermoelectric properties was then investigated. The results show that Sn+ ion implantation can modify thermoelectric properties of the n-type PbTe and greatly improve the dimensionless figure-of-merit.
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    Fractals in Steel-Aluminum Solid to Liquid Bonding
    Peng ZHANG, Yunhui DU, Xueping REN, Limin BA, Hanwu LIU, Jianzhong CUI
    J. Mater. Sci. Technol., 1999, 15 (05): 486-488. 
    This paper studied the fractal characteristic of the interfacial shear surface of steel-Al solid to liquid bonding plate, and determined the relationship between fractal dimension and interfacial shear strength. The research results showed that the relationship between fractal dimension and interfacial shear strength could be described as y=26.2x+4.2 (where y was interfacial shear strength, x was fractal dimension) and when 08Al steel plate was coarsened by steel wire wheel which was made up with steel wires whose diameter were 1.4-1.6 mm, the optimum coarsening pattern of the steel plate surface could be got, the corresponding maximum interfacial shear surface fractal dimension of the bonding plate was 2.33, and the maximum interfacial shear strength of the bonding plate was 65.3 MPa.
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ISSN: 1005-0302
CN: 21-1315/TG
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