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CN 21-1315/TG
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      28 November 2001, Volume 17 Issue 06 Previous Issue    Next Issue
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    Research Articles
    Magnetism of metals, alloys and of clusters of transition metal atoms
    N.H.March
    J. Mater. Sci. Technol., 2001, 17 (06): 581-589. 
    Abstract   HTML   PDF (1945KB)
    A condition for local moment formation in metals derived by Stoddart and March (Ann. Phys. NY 1972 64, 174) is first used to discuss the ferromagnetism of body-centred-cubic Fe. A less detailed discussion is also added on Ni and Co. This leads into a treatment of the nonlinear response of such 3d ferromagnets to dilute substitutional impurities. Antiferromagnets responding to local changes in the exchange field caused by such impurities are also studied, Mn in Cr being one such system discussed. The paper concludes with a brief summary of clusters of transition metal atoms, with most attention devoted to Cr and to Mn.
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    Development of Mg-based hydrogen storage alloy
    Lian bang WANG, Yijing WANG, Huatang YUAN
    J. Mater. Sci. Technol., 2001, 17 (06): 590-596. 
    Abstract   HTML   PDF (1301KB)
    Mg-based hydrogen storage alloys are considered as a promising candidate for hydrogen system because of its lightweight, high storage capacity, low price and rich mineral resources. In detail, we reviewed the preparation and properties of Mg-Ni-based hydrogen storage alloys. All kinds of attempts have been done to improve the hydriding and dehydriding behaviors. It is found that the partial substitution of foreign elements can decrease the hydrogen absorption temperature, especially the substitution of a more electronegative element, such as AI and Mn. Mechanical alloying (MA) and mechanical grinding (MG) are the most effective methods to improve the hydriding/dehydriding kinetics and electrochemical capacity, and decrease the desorption temperature. but the corrosion resistance is so poor that the 80% of maximum capacity is lost within ten cycles. Microencapsulation is a useful measurement for improving the corrosion resistance and electrocatalytic activity. fn order to improve the properties of the alloys for practical application, the alloys should have a large number of defects, which give activated sites, subsequently, MA, MG and electroless plating should be used to improve the hydriding/dehydriding kinetics and protect the surface of alloys, respectively. The new composite Mg-based alloys give a new way for the hydrogen storage material to practical application. Furthermore we put forward several problems which will be discussed in future.
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    Regularities of formation of ternary intermetallic compounds between one transition element and two non-transition elements
    Lixiu YAO, Nianyi CHEN, Jie YANG
    J. Mater. Sci. Technol., 2001, 17 (06): 597-600. 
    Abstract   HTML   PDF (646KB)
    The pattern recognition methods and a four-parameter model, Eased on extension of Miedema's cellular model of alloy phases, are used to study the regularities of formation of ternary compounds between one transition element (T) and two non-transition elements (N, N') (T-N-N' system). The influences of phi (electronegativity), n(ws)(1/3)(valence electron density in Wagner-Seitz cell), R(Pauling's metallic radii) and Z (number of valence electrons in atom) on the formation of the ternary intermetallic compounds were investigated.
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    Vacancies and antisites in B2FeAl and DO3 Fe3Al with a modified analytic EAM model
    Xiaolin SHU, Wangyu HU, Hanning XIAO, Huiqiu DENG, Bangwei ZHANG
    J. Mater. Sci. Technol., 2001, 17 (06): 601-604. 
    Abstract   HTML   PDF (822KB)
    A simple modified analytic EAM model for bcc Fe and fcc AI was used to calculate the lattice constant and elastic constants of B2 FeAl and DO3 Fe3Al alloys. The formation energies of vacancy and antisite were also calculated. The present calculations are in agreement with the experimental data and the theoretical results obtained by other authors.
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    Yield vertices for symmetric slip on {110} < 111 > and asymmetric slip on {112} < 111 > systems
    Zhiyong CHEN, Xinming ZHANG, Churning LIU, Zhuoping ZHOU, Yang YANG, Saiyi LI
    J. Mater. Sci. Technol., 2001, 17 (06): 605-609. 
    Abstract   HTML   PDF (17038KB)
    The single crystal yield surfaces (SCYS) of bcc metals for symmetric slip on {110} (111) and asymmetric slip on {112} (111) systems have been analyzed and deduced. The complete SCYS have been derived when their critical resolved shear stresses (CRSS) are specified in a particular case (such as for Mo metal). The results showed that there are 600 stress states that can be classified into 35 groups according to the crystal symmetry. Each group activates eight, six or five {110} (111) and {112} (111) slip systems depending on crystallographically nonequivalent slip systems groups. Among all these stress states, three groups activate eight systems, there are 24 stress states, four groups activate six systems, there are 48 ones, the remaining twenty-eight groups activate five systems, there are 528 ones. In this case, the fraction of vertices for which there is slip ambiguity (more than five active systems) is reduced considerably compared with pure {110} (111) slip.
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    Shrinkage behaviour of spheroidal graphite cast iron in green and dry sand molds for the benchmarking of solidification simulation
    Wenzhen LI, Baicheng LIU, Jiarong LI
    J. Mater. Sci. Technol., 2001, 17 (06): 610-614. 
    Abstract   HTML   PDF (879KB)
    The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.
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    Effect of pouring process on the microstructures of semi-solid AlSi7Mg alloy
    Weimin MAO, Chenglin CUT, Aimin ZHAO, Jilian YANG, Xueyou ZHONG
    J. Mater. Sci. Technol., 2001, 17 (06): 615-619. 
    Abstract   HTML   PDF (2370KB)
    The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in the paper. When the pouring temperature is close to the liquidus temperature, the primary α-Al in 'the billets of AlSi7Mg alloy solidified into spherical and nodular fine grains distributed homogeneously. The optimum pouring temperature for semi-solid AlSi7Mg billet with spherical or nodular primary α-Al is 615℃. At the same pouring temperature, the higher the pouring ladle, the more easily the spherical and nodular primary alpha -Al obtained in the semi-solid AlSi7Mg billet. When the pouring temperature is close to the liquidus temperature and the pouring ladle is relatively high, it is the great cooling rate, the flow of the molten allay caused by pouring and the large simultaneous solidification region induced by the near liquidus temperature, that promote the formation of spherical or nodular primary α-Al.
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    Subcritical crack-growth and lifetime behavior of glass and SiG under static load
    Yiwang BAO, Qisheng FAN, Shengbiao SU
    J. Mater. Sci. Technol., 2001, 17 (06): 620-624. 
    Abstract   HTML   PDF (1016KB)
    Crack initiation and subcritical crack growth in glass sheet and SiC bar specimen under static loading were investigated to study the failure process. It has been demonstrated that the lifetime process of brittle materials involves three possible forms of crack growth: subcritical crack growth, partly subcritical crack growth and instantaneous fracture without subcritical crack growth. Curves of upsilon -K obtained in step-by-step static fatigue tests and in constant loading rate tests showed different trends for borosilicate glass sheet. alpha -SiC that is generally considered immune to mechanical fatigue effect and environmental attack was also tested under static loading and the lifetime was measured. The results showed that the threshold load to damage effect was over 80% of the initial strength for the SiC.
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    A study on numerical simulation of core-shooting process
    Junjiao WU, Yi GUI, Wenzhen LI
    J. Mater. Sci. Technol., 2001, 17 (06): 625-628. 
    Abstract   HTML   PDF (862KB)
    In order to evaluate the main factors influencing the core-shooting process and to optimize the design of core boxes, the fluid-particle (air-sand) model has been built based on the two-phase flow theory. The fluid phase, air, and the particulate phase, sand granules, have been treated as a continuum. By using this model, it is possible to simulate the flow and compaction behavior of sand particles during the core-shooting process. To benchmark the calculated results, the shooting process has been recorded with a digital high speed camera, and the inlet condition of sand particles has also been achieved by using the camera. The preliminary results have showed that the calculation is in agreement with the testing results.
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    Behavior of Zr-rich phase in a cast NiAl-33.5Cr-0.5Zr alloy during heat treatment
    Hui LI, sJianting GUQ, Wanhui LAI, Shuhe WANG
    J. Mater. Sci. Technol., 2001, 17 (06): 629-632. 
    Abstract   HTML   PDF (1483KB)
    There are many Zr particles in as-cast NiAl-33.5Cr-0.5Zr (at. pct) alloy, which usually exist at the edge of eutectic of beta -NiAl and cx-Cr. After air and furnace cooling solution treatments, far 1400 degreesC, 2 h and 1450 degreesC, 1 h, pure Zr phase remains in the furnace cooling (F.C.) state alloys and Ni2AlZr phase forms in the air cooling (A.C.) state alloys. During solution treatment at 1450 degreesC, bulk and "fish bone" shape Zr-rich phases form respectively in F.C. and A.C. state alloys. A 'river' shape Ni2AlZr phase forms after 1450 C for 1h F.C. and 850 degreesC for 12 h, F.C.. The alloy has less pure Zr and Ni2AlZr phase after 1400 degreesC with both air and furnace cooling followed by 850 C and 950 C for 12 h, F.C. aging treatments, respectively. Additionally, there is a ternary eutectic of NiAlZr and a phase enriched Zr and Cr forms at the edge of the eutectic of beta -NiAl and alpha -Cr in the alloy treated at 1400 degreesC, 2 h, F.C. and 950 degreesC, 12 h, F.C.
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    Evolution of microstructure and mechanical property during long-term aging in Udimet 720Li
    Lanzhang ZHOU, Valentino LUPINC, Jianting GUO
    J. Mater. Sci. Technol., 2001, 17 (06): 633-637. 
    Abstract   HTML   PDF (1745KB)
    Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary gamma' particles maintain good thermal stability at 650 and 700℃ with aging time up to 3000 h, while the tertiary gamma' is apparently dependent on aging temperature and time. The tertiary gamma' particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temperature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the gamma' precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700℃. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary gamma' during aging.
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    Interatomic potentials for some binary oxides
    M.Nadeem, M.J.Akhtar, R.Shaheen, M.N.Haque, A.Y.Khan
    J. Mater. Sci. Technol., 2001, 17 (06): 638-642. 
    Abstract   HTML   PDF (1016KB)
    Using atomistic computer simulation methods we have derived a new set of interatomic potential parameters for some binary oxides, comprising divalent transition elements (rock-salt structured) and tetravalent metals. Computational techniques based on the minimization of the crystal energy with respect to atomic coordinates have been employed. Crystal properties were calculated and compared with the experimental data to check the reliability of our potential models. Intrinsic (Schottky and Frenkel) defect energies were also calculated and compared with previous studies. There is a good agreement between these calculations, which shows that the new potential parameters are reliable and can be used with confidence for future investigations.
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    Effects of O-2 plasma treatment on the chemical and electric properties of low-k SiOF films
    Pengfei WANG, Shijin DING, Wei ZHANG, Jitao WANG, W. W.Lee
    J. Mater. Sci. Technol., 2001, 17 (06): 643-645. 
    Abstract   HTML   PDF (626KB)
    With the progress of ULSI technology, materials with low dielectric constant are required to replace SiO2 film as the interlayer to scale down the interconnection delay. Fluorinated Si oxide thin films (SiOF) are a promising material for the low dielectric constant and the process compatibility in existing technology. However, SiOF films are liable to absorb moisture when exposed to air. By treating the SiOF films with O-2 plasma, it was found that the moisture resistibility of SiOF films was remarkably improved. The mechanism of the improvement in stability of dielectric constant was investigated. The results show that: 1) F atoms dissociated from the films and the bond angle of Si-O-Si decreased. 2) The plasma treatment enhanced the strength of Si-F bonds by removing unstable =SiF2 structures in the films. Resistibility of SiOF films in moisture was improved.
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    Fabrication of Al/Al2O3 composites and FGM
    Hong TAO, Chengji DENG, Lianmeng ZHANG, Runzhang YUAN
    J. Mater. Sci. Technol., 2001, 17 (06): 646-648. 
    Abstract   HTML   PDF (600KB)
    Al/Al2O3 composites of different ratios were hot-press sintered at 575 similar to 640℃ under a pressure of 30 MPa for 2 h in a vacuum furnace. It was found that the relative density of the Al/Al2O3 composites could be increased evidently with the rise of sinter temperature. No reaction occurred between Al and Al2O3 at the sinter temperatures. Under 640℃-30 MPa-2 h experimental condition, Al/Al2O3 system FGM was successfully fabricated, and its density range changed quasi-continuously from 2.887x10(3) kg/m(3) to 3.1909x10(3) kg/m3 within the middle 1.0 mm thickness range.
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    SEM in-situ fracture observation and the reinforcing effect of composite SiCp/ZA22
    Jun WANG, Baode SUN, Yaohe ZHOU, Lining ZHANG, Feng CHEN
    J. Mater. Sci. Technol., 2001, 17 (06): 649-652. 
    Abstract   HTML   PDF (1113KB)
    The strengthening effect of a Zn alloy reinforced by SiC particulate was examined. Based on the results of SEM in-situ fracture observation and stress field analysis by finite element method, it is believed that the reinforcing effect of this composite is due to the combination of strain and stress hardening in the matrix.
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    Superplasticity in an aluminum alloy 6061/Al(2)O(3)p composite
    Lihong HAN, Jitai NIU, Darning JIANG, Tsunernichi Imai
    J. Mater. Sci. Technol., 2001, 17 (06): 653-656. 
    Abstract   HTML   PDF (839KB)
    The superplasticity of an Al(2)O(3)p/6061Al composite, fabricated by powder metallurgy techniques, has been investigated. Instead of any special thermomechanical processing or hot rolling, simple hot extrusion has been employed to obtain a fine grained structure before superplastic testing. Superplastic tensile tests were performed at strain rates ranging from 10(-2) to 10(-4) s(-1) and at temperatures from 833 to 893 K. A maximum elongation of 200% was achieved at a temperature of 853 K and an initial strain rate of 1.67x10(-3) s(-1). The highest value obtained for the strain rate sensitivity index (m) was 0.32. Differential scanning calorimeter was used to ascertain the possibility of any partial melting in the vicinity of optimum superplastic temperature. These results suggested that no liquid phase existed where maximum elongation was achieved and deformation took place entirely in the solid state.
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    Effect of current density on Al alloy microplasma oxidation
    Shigang XIN, Zhaohua JIANC, Fuping WANG, Xiaohong WU, Liancheng ZHAO, Tadao SHIMIZU
    J. Mater. Sci. Technol., 2001, 17 (06): 657-660. 
    Abstract   HTML   PDF (777KB)
    The microplasma oxidation process of LY 12 Al alloy in Na2SiO3-KOH-NaAlO2 system has been studied. The voltage-time curve of oxidation process is changed with the variation of current densities. The voltage breakdown and hardness of coating increase with increasing current density. The phase composition, morphologies, element and the distribution of ceramic coating are investigated by XRD, EPMA.
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    Possibility of inducing compressive residual stresses in welded joints of SS400 steels
    Quanhong LIN, Jing CHEN, Huaining CHEN
    J. Mater. Sci. Technol., 2001, 17 (06): 661-663. 
    Abstract   HTML   PDF (462KB)
    Since the welded constructions produce easily stress corrosion cracking (SCC) or fatigue disruption in corrosive medium or under ripple load, two methods inducing compressive stress on structural surfaces by anti-welding-heating treatment (AWHT) and explosion treatment (ET) are presented. The results show that they are good ways to resisting SCC on the welded SS400 steel or other components.
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    Effects of Dispex A40 on rheology and filter pressing behaviours of concentrated alumina suspensions
    Renjie ZENG, B.R
    J. Mater. Sci. Technol., 2001, 17 (06): 664-666. 
    Abstract   HTML   PDF (594KB)
    Variation of plastic viscosity and extrapolated shear yield stress with the concentration of Dispex A40 for the concentrated Alcoa A16 alpha -Al2O3 suspensions at 0.27 powder volume fraction was investigated at 294 K. An optimum level of Dispex A40 for full deflocculation is found to be at 0.18% mass fraction of the powder, at which the rheological behaviour shows little different to that of adjusting the pH to 4 to obtain full deflocculation. It is demonstrated that the shear stress drop can roughly work as an index for the thixotropy in particular fixed conditions, and consequently an index for the deflocculation as the shear stress drop becomes larger when the level of the flocculation increases, and vice versa. It is also found that the addition of Dispex A40 can prevent the filter cakes from cracking, whereas the cakes at various pH values with polyvinyl alcohol as a sole polymer normally develop cracking during drying.
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    Electrical conductivity and infra red of CaTiO3 doped with CuO
    F.F.Hammad, M.Sh.Khalil, A. H. Salama
    J. Mater. Sci. Technol., 2001, 17 (06): 667-669. 
    Abstract   HTML   PDF (595KB)
    The electrical conductivity of pure CaTiO3 and that containing 0.5 similar to5.0 mole fraction CuO as dopant were measured in the temperature range 291 similar to 773 K. The conductivity values varied as a function of temperature and dopant concentration. The activation energy in the lower temperature range depended on the impurity content while in the high temperature range it indicated a value of energy gap width. The infrared absorption spectra in the range of 100 similar to 4000 cm(-1) revealed the presence of two main bands at 340 and 570 cm(-1) which were assigned to TiO6 octahedral normal mode. Bands in the range of 106 similar to 270 cm(-1) were due to the vibration of anion TiO3-2. Some bands were observed at higher values due to the presence of lattice imperfections. There was a slight shift in band position with increasing dopant concentration which favors the formation of orthorhombic modification.
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    Study of in-situ electrochemical SSCC/HE susceptibility probe
    Xueyuan ZHANG, Enhou HAN, Yuanlong DU
    J. Mater. Sci. Technol., 2001, 17 (06): 670-672. 
    Abstract   HTML   PDF (629KB)
    An in-situ probe technique with an outward attached type of electrochemical sensor for inspection and evaluation of the susceptibility to sulfide stress corrosion cracking (SSCC) and hydrogen embrittlement (HE) of pipeline/vessel was developed. The relationship between SSCC/HE susceptibility of steel UNS G10180 and UNS G11190 and I-H was determined by the measurement of the stable hydrogen permeation rate (I-H) and the study of SSCC/HE susceptibility of the above two steels in TM-01-77 solution. Environmental sensitive cracking (ESC) of UNS G10180 and UNS G11190 steels can be inspected, evaluated, judged by the combination with the microcomputer system (MCS)/periphery attachment and the designed software. The results give an important insurance for safety control of the pressurized pipeline/vessel operated in the environment with H2S.
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    Injection molding of W-Ni-Fe nanocomposite powder prepared by mechanical alloying
    Xuanhui QU, Jinglian FAN, Baiyun HUANG
    J. Mater. Sci. Technol., 2001, 17 (06): 673-674. 
    Abstract   HTML   PDF (375KB)
    Nanocrystalline 90W-7Ni-3Fe (wt pct) composite powder was prepared by mechanical alloying and mixed with binder to form a feedstock. Its rheological and sintering behaviors were compared with those of the feedstock from the original powder. It is found that milling can increase the maximum powder loading of feedstock and enhance the sintering densification process.
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    Effect of hot deformation on microstructure and hardness of in-situ TiB2/7075 composite
    Lin GENG, Jie ZHANG, C.Bartels, G. Gottstein
    J. Mater. Sci. Technol., 2001, 17 (06): 675-676. 
    Abstract   HTML   PDF (591KB)
    Hardness of the TiB2/7075 composite increased with increasing deformation temperature. In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about 1 mum in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 300℃, some of the large precipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450℃, all the precipitates in the annealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.
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    Mechanism of burn resistance of alloy Ti40
    Yongqing ZHAO, Lian ZHOU, Kanging ZHU, Henglei QU, Huan WU
    J. Mater. Sci. Technol., 2001, 17 (06): 677-678. 
    Abstract   HTML   PDF (650KB)
    The Ti fire found in high performance engines promotes the development of burn resistant Ti alloys. The burn resistant mechanism of Ti40 alloy is investigated. Ti40 alloy reveals good burn resistance. Its interfacial products between burning products and the matrix are tenacious, which retard the diffusion of oxygen into the matrix. Two burn resistant mechanisms, that is, fast scatter dispersion of heat and suppression of oxygen diffusion, are proposed.
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ISSN: 1005-0302
CN: 21-1315/TG
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