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ISSN 1005-0302
CN 21-1315/TG
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      28 November 1996, Volume 12 Issue 6 Previous Issue    Next Issue
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    Articles
    Micromechanism of Crystallization in Multicomponent Metallic Glass
    Jianmin LP; Mingxiu;QUAN and Zbuangqi HU (National Key Lab. of RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 401-408. 
    Abstract   HTML   PDF (1662KB)
    A micromechanism in an atomic level of crystallization of transition metal-metalloid TM80M20 metallic glass is thermodynamically proposed by taking Bernal polyhedra as the starting structure of metaIlic glass. It is composed of two competitively processes: (i) densification process of atom cluster leads to the formation of the precursor in amorphous matrix, (ii) the growth of atom cluster leads to the decreasing packing density. The preferential precipitation sequence of metastable phase is bcc, bct. cpc (close-packed crystal, hcp or fcc structure). A metastable phase decomposition (Fe,Mo)23B6 (fcc)-Fe2B highly strained bct phase was observed during crystallization of (Fe0.99Mo0.01)78Si9B13 metallic glass, which is related to the occurrence of nanocrystalline.
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    Microstructure and Mechanical Property of Nanocrystalline NiZr_2 Intermetallic Compound
    Xuedong LIU;Fuhe YUAN; Ke LU and Wenduo WEI (National Lab. for RSA, Institute of Metal Research, Chinese Acedemy of Sciences, Shenyang 110015, China)(To whom correspondence should be addressed)( Present address: National Lab. of Corrosion Science and Prot
    J. Mater. Sci. Technol., 1996, 12 (6): 409-412. 
    Abstract   HTML   PDF (1533KB)
    Single-phase NiZr2 intermetallic compound nanocrystalline samples were synthesized by fully crystallizing the parent amorphous NiZr2 alloy at the temperature interval of 653~1073 K for a certain period of time. High resolution electron microscope (HREM) observations on the nanophase NiZr2 reveal a Iamellar nano-tWin structure with (110) direction on the nanometer scale, being typically a few interatomic distances to a few nanometers. Microhardness measurements on the single-phase NiZr2 samples indicate that the hardness of nanotwinned NiZr2 is obviously increased in comparison to the amorphous counterpart. When the average grain size increases from 19.1 to 93.9 nm, the variation of the hardness with the average grain size obeys the normal Hall-Petch relation, whereas as the average grain size is smaller than 19.1 nm. the microhardness data deviate from the above relation.
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    Dependence of Structural and Optoelectrical Properties on the Composition of Electron Beam Evaporated Zn_xCd_(1-x)S Thin Films
    Shahzad Naseemt and M.Amin Mughal (To whom correspondence should be addressed)(Centre for Solid State Physics, University of the Punjab, Lahore-54590, Pakistan)M.Y.Zaheer, N.Ahmed and M.Akram (Dept. of Physics, University of the Punjab, Lahore-54590, Paki
    J. Mater. Sci. Technol., 1996, 12 (6): 413-416. 
    Abstract   HTML   PDF (355KB)
    Thin films of ZnxCd1-xS have been prepared by electron beam evaporation of a mixture of ZnS & CdS powders. The films are deposited onto sodalime glass slides under similar conditions.The composition of the films is varied from CdS to ZnS (x=0 to 1). The films show a regular change in color from toner red to orange yellow as Zn concentration increases to maximum.These films are characterized for their optical, electricaI and structural properties. The bandgap value of ZnxCd1-xS films is found to vary linearIy from 2.20 eV to 3.44 eV with change in the x value from 0 to 1. The resistivity of these films is in the range of 171.0 Ωcm to 5.5× 106Ωcm for x=0~0.6. All the samples show cubic structure after annealing in air at 250℃ for 40 min.The lattice constant ao varies from 0.5884 nm to 0.54109 nm linearly.
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    Structural and Electrical Properties of Cobalt Ferrite
    C.O.Augustin; L.K.Srnivasan; P.Kamaraj and A.Mani (Central Electrochemical Research Institute, Karaikudi-630006, India)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 417-420. 
    Abstract   HTML   PDF (1344KB)
    Ferrites are a class of cohesive new materiafs required for many specialised applications. Cobalt ferrite (CoFe2O4) has been identified as a substitute for carbon and serves as a non consumable anode for an eco-friendly and energy efficient production of aluminium. Pellets of cobalt ferrite have been prepared by powder metallurgical process and their electrical properties have been investigated from ambient temperature to 1273 K. The structural and morphological features have been studied by X-ray diffraction and scanning electron microscopy The relationships between such properties, chemical composition and sintering temperatures are thoroughly discussed.
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    Effect of Wetting and NiAl_2O_4 Spinel Formation on the Bonding between Al_2O_3 and Ni
    Xudong SUN and J.A. Yeomans (Dept. of Materials Science and Engineering, University of Surrey Guildford, Surrey GU2 5XH, UK (To whom correspondence should be addressed Present address: Dept. of Materials Science and Engineering, Northeastern University,
    J. Mater. Sci. Technol., 1996, 12 (6): 421-426. 
    Abstract   HTML   PDF (3702KB)
    Al2O3-Ni interface formed under vacuum condition is non-wetting and weak. Severe instantaneous intedecial reaction (i.e. wetting) at the Al2O3-Ni interface promoted by oxygen can create a strengthened interface. The NiAl2O4 spinel-Ni intedece is weak and growth of the spinel interphase is detrimental to the Al2O3-Ni intedecial bonding. A proper control of the oxygen partial pressure can achieve wetting while avoiding the existence of spinel at the interface, producing stronger interfaces by both mechanical interlocking and more intimate chemical bonding in an Al2O3-20 vol pct Ni composite.
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    Electronic Structure of the Clusters Containing Oxygen in Ni
    Tao YU; Chongyu WANG and Bing WANG (Central Iron and Steel Research Institute, Beijing 100081, China)(To whom correspondence should be addressed)( The International Centre for Materials Physics of the Chinese Academy of Sciences, Shenyang 110015, China)
    J. Mater. Sci. Technol., 1996, 12 (6): 427-433. 
    Abstract   HTML   PDF (567KB)
    The electronic structure of the clusters containing oxygen, the stacking fault and the complex in the transition metal Ni are calculated by the multiple-scattering Xa method. Energy levels,density of states and transfer of charge are obtained. Based on the calculation and analysis,the influences of impurity oxygen and structure defect on the electronic structure of the clusters are discussed, and it is found that the local Ni-o cluster with the interstitial oxygen is a stable atomic configuration.
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    Structural Evolution of the Mn_(0.52)Sb_(0.48) Compound during High Energy Ball Milling
    Fuxing YIn and Nanju GU (Dept. of Materials Science and Engineering, Hebei Institute of Technology, Tianjin 300130, China)T.Shigematsu and N.Naknishi (Dept. of Chemistry, Faculty of Science, Konan University, Kobe 658, Japan)(To whom correspondence should
    J. Mater. Sci. Technol., 1996, 12 (6): 434-438. 
    Abstract   HTML   PDF (574KB)
    The structural transitions of the NiAs-type Mn0.52Sb0.48 magneto-ordered compound, ball milled to different periods, have been characterized by X-ray diffraction and DSC analysis. On the basis of lattice parameter results a structural evolution mode with three stages is proposed. In the first stage lattice parameters keep nearly unchanged with the refinement of grains and increase of lattice strain. In the second stage, microstrain shows a lowering tendency accompanying the successive decreases of grain size. The X-ray revealed internal strain is found to be strains inside the lattice, which can be relaxed with new grain formation. The change of Tc is shown to be affected by the dimension of c axis, however the overall magnetization is continuously decreased with milling, due to the disordering process occurred in milling. Correspondent disordering mechanisms have been tentatively postulated and discussed according to the changes of lattice para meters.
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    Preparation and Characterization of Ultrafine ZrO_ Powders from Solvent Extraction of Zr(Ⅳ) with Tri-n-butyl Phosphate in Kerosene from Nitric Acid Solutions
    Chuanfang YANG and Jiayong CHEN (Institute of Chemical Metallurgy, Chinese Academy of Sciences, Beijing 100080, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 439-444. 
    Abstract   HTML   PDF (1106KB)
    Zr(IV) was extracted by tri-n-butyl phosphate in kerosene from concentrated nitric acid solutions and the formation of the third phase during extraction was experimentally investigated. Zirconia powders were prepared by using the loaded organic phase as the bulk solution precipitated with aqueous ammonia or NaOH solution. The powder prepared was characterized with TEM, XRD,EDAX and TG-DTA. Effects of some conditions on powder preparation were studied and it was shown that nanosized particles could be obtained from this extraction system but conditions should be carefully controlled for powder purity and particle size.
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    Hot Corrosion of Iron in the Presence of Salt Mixture Deposit Containing NaCl and V_2O_5 at 600℃
    Lingchuan LI (Dept. of Materials Science and Engineering, Tsinghua University Beijing 100084, China)Rizhang ZHU (Dept. of Surface Science and Corrosion Engineering, University of Science and Technology Beijing, Beijing 100083, China)(To whom correspondenc
    J. Mater. Sci. Technol., 1996, 12 (6): 445-451. 
    Abstract   HTML   PDF (1537KB)
    Iron suffered low temperature hot corrosion (LTHC) in the presence of salt deposits of Na2SO4,Na2SO4 mixed with NaCl and Na2SO4 mixed with V2O5 in a combustion gas at 600℃. The additions of NaCl to Na2SO4 and of V2O5 to Na2SO4 changed the corrosion kinetics significantly and modified the scale structure markedly It is proposed that trivalent iron ions were more favored than divalent ions in the eutectic responsible for the occurrence of LTHC when NaCl was present, while the reaction between Na2SO4 mixed with V2O5 and the gas formed (Na2O)xV2O4(V2O5)6-x providing directly the liquid required by LTHC. The suphide formation in the inner FeO larer was related to the sites of the reduction step wher SO2 was released.
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    Microstructure and Fracture Morphology in the Welding Zone of Cr18Mo2 Ferritic Stainless Steel
    Yajiang LI; Zengda ZOU and M. Thompson (Dept. of Materials Engineering, Shandong University of Technology, Jinan 250061, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 452-456. 
    Abstract   HTML   PDF (3810KB)
    Microstructure, precipitates and fracture morphology in the weld metal and the heat-affected zone (HAZ) of Cr18Mo2 ferritic stainless steel have been studied by means of metalloscope, SEM,TEM and X-ray diffractometer. Experimental results indicate that crystalline grain coarsening in HAZ is one of the reason resulting in the embrittlement fracture in the welding zone of the ferritic stainless steel. Some precipitates (TiC, TiN and Cr2N) in the steel promote production and development of the brittle cracks. In practical applications. the welding heat input should be as small as possible to prevent embrittlement caused by HAZ grain coarsening.
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    Molecular Electrical Conductor Ni(C_3S_5)_2
    Hong LEI (Dept. of Electronic Engineering, Shandong University, Jinan 250100, China)Qi FANG and Minhua JIANG (Institute of Crystal Materials, Shandong University, Jinan 250100, China)Yueming SUN (Dept. of Chemistry Southeast University Nanjing 210093, Chi
    J. Mater. Sci. Technol., 1996, 12 (6): 457-460. 
    Abstract   HTML   PDF (350KB)
    The molecular based electrical conductor Ni(C3S5)2 has been prepared and its conductivity has been measured from room temperature down to 60 K. Above 167 K Ni(C3S5)2 exhibits a semiconductive behaviour, below this temperature it turns to exhibit metallic conductivity. Based on a tight-binding energy band calculation, an expression for the number of conducting electrons has been deduced. The calculated conducting activation energy is quite well in accordance with the measuring value.
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    Characterization of Nanocrystalline Intermetallic Compound NiAl Synthesized by Condensation
    Yong QIN; Xiaoying QIN and Lide ZHANG (Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 461-463. 
    Abstract   HTML   PDF (1367KB)
    Nanocrystalline intermetallic compound NiAl was Synthesized by evaporating NiAl master alloy in inert-gas followed by in situ compaction, and its structure was studied by means of X-ray diffractometry and transmission electron microscope. Experimental results reveal that the assynthesized nanocrystalline sample has a mean grain size of less than 10 nm and it is dominantly composed of the cubic structure phase NiAl. However, nanocrystalline Ni3Al as a trace phase mixed in NiAl phase, was also detected by transmission electron microscope observation.
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    Stoichiometric NbTiAl_3 (γ1 Phase) Alloy in Ti-Al-Nb Ternary System
    Jingxia CAO; Jinjun DING and Shiming HAO (Dept. of Materials Science and Technology, Northeastern University Shenyang 110006, China)(To whom correspondence should be addressed)Guoliang CHEN (Dept. of Materials Science and Technology University of Science
    J. Mater. Sci. Technol., 1996, 12 (6): 464-466. 
    Abstract   HTML   PDF (1127KB)
    The microstructure and phase constitution in stoichiometric NbTiAl3 (γ1 phase) alloy treated at 1000℃ were examined by metallography and X-ray diffraction. The alloy microstructure is mainly γ1 phase containing η second phase [(Ti,Nb)Al3] less than 1%. DTA analysis shows no phase transformation from room temperature to 1200℃. In the diffusion couple of NbTiAl3 with 7-TiAl compound, clear phase boundary and composition jump exist between γ1 and γ phase.These results further confirm the existence of γ1 single phase at 1000℃ in Ti-Al-Nb ternary system.
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    Diffusion Bonding of Ti_3Al Base Alloy
    Yi GUO; Jinman ZHU;Zhijing HE; Pifen LIAN and Qing WU (Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China)(To whom correspondence should be addressed)Hong ZHANG (Weihai University, Weihai 260000, China)
    J. Mater. Sci. Technol., 1996, 12 (6): 467-469. 
    Abstract   HTML   PDF (2134KB)
    : The effects of diffusion bonding temperature and holding time on the joint strength of Ti3Al base alloy has been investigated in this paper. The shear strength of Ti-14Al-21Nb-3Mo-V alloy diffusion bonding joint under pressure of 12 MPa at 990℃ for 70 min was obtained to 797.6 MPa which approaches the base material strength. In addition, a short-time diffosion bonding process was studied in order to decrease the bonding cost. With the deformation of the specimens of 2.5% and the bonding temperature of 990℃ for 15 min, the bonding strength could reach 801 MPa.
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    A Positron Study of Hysteresis Temperature in Ti-Ni Alloy
    Jingcheng WANG and Guiying QIN (Shanghai Key Lab. of Metal Functional Materials, Shanghai Iron and Steel Research Institute, Shanghai 200940, China)(To whom correspondence should be addressed)Guilin ZHANG ana Wanhui ZHENG (Shanghai Nuclear Research Instit
    J. Mater. Sci. Technol., 1996, 12 (6): 470-472. 
    Abstract   HTML   PDF (1192KB)
    For Ti-Ni alloy it is exceedingly difficult to prepare an element that has a desired and defined hysteresis temperature for its preparing process is not pedect at present. Because the mechanism of transformation in Ti-Ni has not been fully clarified, it is far more exceedingly difficult to explain the hysteresis temperature only by using the traditional metal physics techniques., But positron annihilation seems to be a suitable method for it. The positron annihilation measurements showthat the hysteresis temperature may be controlled mainly by the relative fraction of the defectscontained in a two-way shape memory element.
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    Choice of Parameters in Morse Potential for Copper
    Yuming WANG (Dept. of Materials Science, Jilin University Changchun 130023, China)
    J. Mater. Sci. Technol., 1996, 12 (6): 473-475. 
    Abstract   HTML   PDF (306KB)
    The choice of parameters in Morse potential for copper was made by the molecular dynamics modeling. The elastic coefficients C11, C44, their temperature coefficients TC11, TC44, as well as the hydrostatic compression behaviour, i.e. pressure/volum curvs have been calculated. The choice of Morse poteotial parameters can be made by comparing the results with the experimental data. The chosen parameters are greatly different for different simulated properties.
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    Dislocations in the Crystallites of Nanocrystalline α-Fe —A Molecular Dynamics Study
    Zhiying CHEN and Jiaqans DING (Lab. on Non-linear Mechanics of Continuous Media, Institute of Mechanics, Chinese Academy of Sciences,Beijing 100080, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 476-478. 
    Abstract   HTML   PDF (366KB)
    Molecular dynamics simulations are carried out in order to Study the atomic structure of crystalline component of nanocrystalline α-Fe when it is consolidated from small grains. A two-dimensional computational block is used to simulate the consolidation process. All the preset dislocations in the original grains glide out of them in the consolidation process, but new dislocations can generate when the grain size is large enough. It shows that dislocations exist in the consolidated material rather than in the original grains. Whether dislocations exist in the crystalline component of the resultant model nano-material depends upon grain size. The critical value of grain size for dislocation generation appears to be about 9 nm. This result agrees with experiments qualitatively.
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    Relationship of Initiator Length with Fractal Dimension of Fractured Surfaces of High Strength Steels
    Chiwe LUNG and Zaqin MU (International Ceotre for Materials Physics, Inditute of Metal Research, Chinese Academy of Sciences,Shenyang 110015, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1996, 12 (6): 479-480. 
    Abstract   HTML   PDF (132KB)
    Length-yardstick relation was used for measurement of the fractal dimension and the length of the initiator of Koch curves. It was found that the higher the fractal dimension and then the fracture toughness, the shorter the length of the initiator of the Koch curve for the crack lines would be.
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CN: 21-1315/TG
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