Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      28 January 2003, Volume 19 Issue 01 Previous Issue    Next Issue
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    Research Articles
    Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechanical Attrition
    Xingping YONG, Gang LIU, Ke LU, Jian LV
    J. Mater. Sci. Technol., 2003, 19 (01): 1-4. 
    Abstract   HTML   PDF (1209KB)
    A nanostructured surface layer was synthesized on a low carbon steel by using surface mechanical attrition (SMA) technique. The refined microstructure of the surface layer was characterized by means of different techniques, and the hardness variation along the depth was examined. Experimental results show that the microstructure is inhomogeneous along the depth. In the region from top surface to about 40 mm deep, the grain size increases from about 10 nm to 100 nm. In the adjacent region of about 40-80μm depth, the grain size increases from about 100nm to 1000 nm. The grain refinement can be associated with the activity of dislocations. After the SMA treatment, the hardness of the surface layer is enhanced significantly compared with that of the original sample, which can primarily be attributed to the grain refinement.
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    Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application
    Qiang WANG, Jicheng HE, Satoru KAWAI, Kazuhiko IWVAI, Shigeo ASAI
    J. Mater. Sci. Technol., 2003, 19 (01): 5-9. 
    Abstract   HTML   PDF (1213KB)
    Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate, removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed t o generate intense compression waves directly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a static magnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical model based on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagnetic force. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducer under various conditions. The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structures was also examined. It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.
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    Two Dimension Finite Element Simulations on the Electromagnetic Containment in Twin-Roll Strip Casting
    Peiwei BAO, Hongshuang DI, Xiaoming ZHANG, Guodong WANG, Xianghua LIU
    J. Mater. Sci. Technol., 2003, 19 (01): 9-12. 
    Abstract   HTML   PDF (750KB)
    Distribution of magnetic field and electromagnetic force in twin-roll casting of steels was studied by the method of numerical simulation in this paper. Two-dimension finite element model, which includes the regions of melt, stainless collar, coil and magnetic core, has been constructed. By solving magnetic vector potential formulations of quasi-static electromagnetic field, distribution of magnetic flux density and magnetic force at different molten height is determined. Calculated results showed that intensity of the distribution of magnetic flux density increased linearly with the increased coil current; and the magnetic force in the melt increased as a quadratic cure with creased coil current. More attention was given to the distribution of eddy current and magnetic force in the melt, the confine effect at different molten height was also discussed.
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    Cyclic Fatigue Fracture of Zr55Al10Ni5Cu30 Bulk Amorphous Alloy with Quenched-in Crystallites
    Qingsheng ZHANG, Shiding WU, Haifeng ZHANG, Bingzhe DING, Zhuangqi HU
    J. Mater. Sci. Technol., 2003, 19 (01): 13-15. 
    Abstract   HTML   PDF (1551KB)
    The effects of quenched-in crystallites on the fracture of bulk amorphous alloys under cyclic loading condition were investigated in this paper. For the fully amorphous alloy and specimen with fine crystallites the fatigue crack initiation occurred on the surface. For the specimen with larger crystallites the crack originated from a big broken crystallite near the surface. The average striation spacing on amorphous area is much larger than that on the crystallite. Crack initiation occurred at the crystallites is due to that the brittle crystallites broke easily under cyclic deformation condition. The fine crystallites seemed to be protruded from the amorphous matrix and some bulges appeared on the surface of specimen with fine crystallites under cyclic loading.
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    Density of Liquid Ni-Cr Alloy
    F.Xiao
    J. Mater. Sci. Technol., 2003, 19 (01): 16-18. 
    Abstract   HTML   PDF (464KB)
    The density of liquid Ni-Cr alloy was measured by a modified sessile drop method. The density of liquid Ni-Cr alloy was found to decrease with increasing temperature and Cr concentration in the alloy. The molar volume of liquid Ni-Cr alloy increases with increasing the Cr concentration in the alloy. The molar volume of Ni-Cr alloy determined in the present work shows a positive deviation from the linear molar volume.
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    Oxidation of Hastelloy-XR Alloy for Corrosion-Resistant Glass-Coating
    Rong TU, Takashi GOTO
    J. Mater. Sci. Technol., 2003, 19 (01): 19-22. 
    Abstract   HTML   PDF (1332KB)
    The oxidation behavior of Hastelloy-XR alloy was investigated to obtain the optimum surface condition for corrosion-resistant glass-coatings. The surface morphology of oxide scales changed significantly with variation of temperature and oxygen partial pressure. The oxidation kinetics was mainly parabolic independent of oxidation conditions. The oxide scales were consisted of inner Cr2O3 and outer spinel layers. The phase component of spinel layers were Mn1.5Cr1.5O4 and (Mn,Ni)(Cr,Fe)2O4 for the oxygen partial pressures po2< 10kPa and po2>10kPa, respectively. The optimum oxidation condition to obtain an oxide scale for well-adhered glass-coating to the substrate was 1248K and po2=0.01kPa for the oxidation time of 43ks.
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    Simulations of Temperature Field in HFCVD Diamond Films over Large Area
    Aiying WANG, Chao SUN, Rongfang HUANG, Lishi WEN
    J. Mater. Sci. Technol., 2003, 19 (01): 22-26. 
    Abstract   HTML   PDF (977KB)
    A three-dimensional model was developed to investigate the influence of various hot filaments parameters on substrate temperature fields that significantly affect the nucleation and growth of diamond films over large area by hot-filament chemical vapor deposition (HFCVD). Numerical simulated results indicated that substrate temperature varies as a function of hot filaments number, radius, temperature, emissivity, the distance between filaments, and the distance between substrate and filaments arrangement plane. When these filaments parameters were maintained at the optimal values, the homogeneous substrate temperature region of 76mm×76mm with the temperature fluctuation no more than 5% could be obtained by a 80mm×80mm hot filaments arrangement plane. Furthermore, the homogeneous region could be enlarged to 100mm×100mm under the condition of supplementary hot filaments with appropriate parameters. All of these calculations provided the basis for specially optimizing the hot filaments parameters to deposit uniform diamond film over large area by HFCVD.
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    A Study of AlN Films Prepared by Arc Ion Plating
    Meidong HUANG, Chunyan LU, Bing WANG, Chao SUN, Rongfang HUANG, Lishi WEN, Guoqiang LIN, Chuang DONG
    J. Mater. Sci. Technol., 2003, 19 (01): 27-29. 
    Abstract   HTML   PDF (1082KB)
    Hexagonal AlN films have been obtained by arc ion plating at different negative biases.X-ray diffraction and scanning electron microscopy results show that AlN films with smooth surfaces and (002) preferred orientation are obtained at low biases, whereas those with coarse surfaces and (100) preferred orientation are obtained at high biases. The formation mechanism of AlN is analyzed and the experiment results are discussed. The effect of bias on adhesion strength has also been examined.
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    Electrophoretic Deposition of Hydroxyapatite Coating
    Zude FENG, Qishen SU, Zuochen LI
    J. Mater. Sci. Technol., 2003, 19 (01): 30-32. 
    Abstract   HTML   PDF (721KB)
    Hydroxyapatite (HAP) coatings were deposited onto titanium substrates by electrophoretic deposition (EPD) from ethanol. The results indicated that the addition of very small amount of HCl resulted in a decrease in the aging time as well as the suspension concentration required to obtain a coating. In addition, the results revealed the existence of a critical saturated voltage (Vsat), which had significant effect on the quality of deposition. The mean interfacial shear strengths of HAP coatings after sintering were found to be greater than 13MPa.
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    Influence of Additive Silica on the Laser Melting of the Ceramic Coatings
    Yuanzheng YANG, Xiaojun BAI, Zhiwei XIE, Tongchun KUANG, Zhengyi LIU, Yuzhi ZHUANG, Baiyun TONG, Yong LIANG
    J. Mater. Sci. Technol., 2003, 19 (01): 33-36. 
    Abstract   HTML   PDF (1920KB)
    The influence of additive silica on the microstructure of plasma sprayed Al2O3 and Al2O3+13wt pct TiO2 ceramic coatings at laser melting has been investigated in this study. At the laser melting, additive silica in Al2O3 ceramic coating can reduce the stress of cooling shrinkage generated during solidification. Moreover, silica can render finer size of grains of the melting layer and form continuous glassy matter around the grain boundaries so as to reduce further the cooling stresses and to suppress the formation and spreading of cracks. On the other hand, at the laser melting, TiO2 reacts with Al2O3and transforms into TiAl2O5. The latter new phase has great and anisotropic coefficients of thermal expansion leading to big and asymmetrical stresses and thus to form cracks in the melting layer of Al2O3+13wt pct TiO2 coating. Due to the fact that the influence of additive silica on the suppression of the formation of cracks is rather limited and cannot counterbalance the negative effect of TiAl2O5, thus the melting layer of Al2O3+13wt pct TiO2 coating doped with 3wt pct SiO2 cracks also. Nevertheless, TiO2 can greatly develop the wear resistance of the ceramic coating as sprayed or laser melted.
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    Effect of Film Thickness on the Optical Parameters and Electrical conductivity of Te10Ge10Se77Sb3 Chalcogenide Glass
    Z.El-Gohary, A.Abdel-Aal, A.Elshafie
    J. Mater. Sci. Technol., 2003, 19 (01): 36-40. 
    Abstract   HTML   PDF (834KB)
    Several thin films of Te10Ge10Se77Sb3 chalcogenide glass of different thicknesses (250nm to 400nm) were prepared by thermal evaporation under vacuum of 133 ×10-6 Pa(10-6torr). X- ray diffraction analysis showed the amorphicity of the prepared films which become partially crystalline by annealing. Transmittance and reflectance measurements in the spectral range of 200nm to 2500nm have been carried out at normal incidence. The analysis of the absorption coefficient data showed the existence of indirect transition for the photon energy E in the range 1-3eV and direct transition for E>3eV. From the determination of the optical constants (n, k), the dispersion of the refractive index has anomalous behaviour in the region of the fundamental absorption edge, and followed by the single- effective oscillator approach.The investigated optical parameters such as the optical energy gap Eopt, the high frequency dielectric constant eoo ,the oscillator position lo, and the oscillator strength So, were significantly affected by the film thickness. The characteristic energy gap obtained from the conductivity measurements is nearly half the value of that obtained from the optical data as in the case of thickness 400nm. The activation energy is 0.65 eV and the indirect optical gap is 1.32eV.
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    Instability of Structural, Magnetic, and Magnetoresistive Properties in Ordered Double-perovskite Sr2FeMoO6 Polycrystals
    Jianming DAI, Yijun YANG, Wenhai SONG, Jiaju DU, Yuping SUN
    J. Mater. Sci. Technol., 2003, 19 (01): 40-42. 
    Abstract   HTML   PDF (645KB)
    The problem of instability in polycrystalline ordered double-perovskite Sr2FeMoO6, is presented in this paper. By the X-ray diffraction analysis and the measuring of electrical and magnetic transports, it is indicated that the perovskite structure of the compound is destroyed, and the Sr2FeMoO2 phase is mainly transformed into SrMoO4 phase when the samples are exposed in damp atmosphere for several weeks or immersed in water for several hours. Simultaneously, their electrical and magnetic properties obviously change, and the value of magnetoresistance remarkably reduces and even vanishes at room temperature. A possible micromechanism of the instability and an effective method to avoid the problem of instability are also discussed.
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    Effect of Traveling Magnetic Field on Mould-Filling Length of the A357 Melt during Casting Thin Walled Plate
    Tiejun ZHANG, Jingjie GUO, Yanqing SU, Hongsheng DING, Weisheng BI, Jun JIA, Hengzhi FU
    J. Mater. Sci. Technol., 2003, 19 (01): 43-46. 
    Abstract   HTML   PDF (840KB)
    In order to improve the mould filling ability, the method for production of thin-walled castings in the traveling magnetic field was applied. The relationship between magnetic field density and input voltage as well as distance was investigated, and the mould filling length of A357 melt has been studied. The electromagnetic forces applied on the melt were also analyzed. The result shows that the mould-filling length of the melt increase rapidly with the increase of magnetic flux density. The mould filling lengths in gypsum upper mould and magnetic material upper mould were compared from the standpoint of application. It demonstrated that the steel upper mould is superior to gypsum mould. 2.5mm.
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    A Study on the Density of Agglomerates Prepared from Cork Wastes
    A.Macas-Garcia, A.D'iaz-Parralejo, M.A.D'iaz-D'iez, P.de la Rosa-Blanco, V.G'omez-Serrano
    J. Mater. Sci. Technol., 2003, 19 (01): 46-50. 
    Abstract   HTML   PDF (1093KB)
    The density of black regranulate (BR) of cork and of black agglomerate (BA) and composite agglomerate (CA) prepared from such a waste by different methods was investigated. The preparation of the agglomerates was undertaken by controlling the specimen thickness for BA and the particle size for BR and the binder dosage for CA. The mass changes produced in the oven-drying treatment at 376.15~K of the agglomerates and in their subsequent stabilization under ambient conditions were also analyzed. The density was determined by standard methods. For BR, the bulk density first decreased and then increased with decreasing particle size. It was much lower than the apparent density of the agglomeration products of cork. Although to a lesser extent, the density was also lower for BA than for CA. It was higher for the smaller thickness specimens of BA. In the case of CA, the density followed the same variation trends as for BR. Furthermore it increased significantly with the increase in resin dosage. This resulted in a noticeable increase in the weight loss during the oven-drying and in a significant decrease in the degree of moisture adsorption during the stabilization period of the agglomerate.
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    Study on the Rare Earth Sealing Procedure of the Porous Film of Anodized 2024 Aluminum Alloy
    Xingwen YU, Chuanwei YAN, Chunan CAO
    J. Mater. Sci. Technol., 2003, 19 (01): 51-53. 
    Abstract   HTML   PDF (1504KB)
    The rare earth sealing procedure of the porous film of anodized aluminum alloy 2024 was studied with the field emission scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS). The results show that RE solution can form cerium oxide/hydroxides precipitation in the pores of the anodized coating at the beginning of sealing. At the same time, the spherical deposits formed on the surface of the anodized coating created a barrier to the precipitation of RE solution in the pores. When the pore-structured anodizing film is covered all with the spherical deposits, RE conversion coating will form on the surface of the anodized coating. The reaction of the coating formation was investigated by employing cyclic voltammetry. The results indicate that accelerator H2O2acts as the source of O2 by carrying chemical reaction in course of coating formation. In the mean time, it maybe carries electrochemical reaction to generate alkaline condition to accelerate the coating formation. The porous structure of the film is beneficial to the precipitation of the cerium hydroxides.
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    Vacuum-Aided Recovery Technology of Spent Ni-Cd Batteries
    Jianxin ZHU, Jinhui LI, Yongfeng NIE, Bo YU
    J. Mater. Sci. Technol., 2003, 19 (01): 54-56. 
    Abstract   HTML   PDF (572KB)
    Recovery of Ni-Cd batteries was studied by a self-designed vacuum-aided recovering system under laboratory conditions. The fundamental research on a process of disassembling and recovering selected materials from Ni-Cd batteries was conducted. The impacts of temperature, pressure and time were studied respectively. The mechanism of vacuum thermal recovering was also discussed. The results show that: Ni-Cd batteries can be recovered effectively by vacuum-aided recovering system at 573-1173K. At constant pressure, the increase of temperature can improve the separating efficiency of cadmium. When the temperature is 1173K, the cadmium can evaporate completely from the residue during 3h at 10Pa. The reduction of pressure in the certain range is effective to separate cadmium by vacuum distillation. Distillation time is a very important factor affecting separation of cadmium.
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    Calculation of the Composition Profile of a Functionally Graded Material Produced by Co-sedimentation
    Zhongmin YANG, Lianmeng ZHANG, Qiang SHEN
    J. Mater. Sci. Technol., 2003, 19 (01): 57-59. 
    Abstract   HTML   PDF (520KB)
    A sedimentation method is proposed to fabricate functionally graded materials (FGMs) with the continuous and smooth variations of composition. The relations between the compositional distribution of deposited body and the powder characteristics of raw materials as well as settling parameters are derived. Subsequently, the mathematical model of forming FGM based on the co-sedimentation has been established. At last, numerical simulations are conducted to explore the effects of the particle sizes of raw materials and suspension height on the compositional distribution of final products.
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    Microstructures and Creep Behavior of a Directionally Solidified NiAl-Fe(Nb) Multiphase Intermetallic Alloy
    Yihui QI, Jianting GUO, Chuanyong CUI
    J. Mater. Sci. Technol., 2003, 19 (01): 59-62. 
    Abstract   HTML   PDF (1167KB)
    The microstructure and creep behavior of a DS NiAl-Fe(Nb) multiphase intermetallic alloy have been investigated. This alloy exhibits dendritic structure, in which dendritic arm isβ-(Ni,Fe)(Fe,Al) phase surrounded by interdendritic region ofγ'/γ phase. The results of the creep test indicated that all of the creep curves have similar characteristic, which is a short primary creep stage and a dominant steady state creep stage, and the creep strain ranges from 18% to 52%. The apparent stress exponent and the apparent activation energy were analyzed and discussed. The mechanism of the creep deformation was also analyzed by the observation of TEM.
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    Fabrication of ZrO2/Mo-Si/Ni Functionally Graded Material by Dip-Coating
    Mingwei LI, Jingchuan ZHU, Zhongda YIN, Gang ZENG
    J. Mater. Sci. Technol., 2003, 19 (01): 63-65. 
    Abstract   HTML   PDF (1063KB)
    A slurry dip-coating technique was developed for fabrication of ZrO2/Mo-Si/Ni functionally graded material (FGM) on the stainless steel substrate. The rheological behavior of ZrO2-Ni-ethanol slurry was characterized by viscosity test. The amount of polyvinyl butyral (PVB) additives, which served as the dispersant and binder in ZrO2-Ni-ethanol slurry, was optimized. The results showed that the characters of mixed slurries with added 9vol. Pct (relatively to total powders) MoSi2 powders prepared by mechanical alloying changed little. The stainless steel substrate was coated several times by dipping in the slurries, and followed by drying in air every dipping. After debinding in Ar in graphite die, the coated FGM plate was finally hot pressed at 1300oC for 1h under the pressure of 5MPa in Ar in the same die. Microstructural observations of the sintered FGM specimens revealed that the graded layers were formed on the stainless steel substrate, in which no cracks were observed
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    Application of Substitutional Model in Oxide Systems
    Lin LI, O.Van Der Biest, Peiling WANG
    J. Mater. Sci. Technol., 2003, 19 (01): 66-68. 
    Abstract   HTML   PDF (492KB)
    The application of substitutional model in oxide systems, in comparison with that of sublattice model, is discussed. The results show that in the case of crystalline phases and liquid phases without molecular-like associates or the shortage of element in sublattice, these two models get consistent in the description of the formalism of Gibbs free energies of phases and obtain the same result of phase diagram calculation when the valence of the cations keep the same.
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    Desulphurization during VIM Refining Ni-base Superalloy using CaO Crucible
    Jianping NIU, Kenu YANG, Tao JIN, Xiaofeng SUN, Hengrong GUAN, Zhuangqi HU
    J. Mater. Sci. Technol., 2003, 19 (01): 69-72. 
    Abstract   HTML   PDF (708KB)
    The variation of S content during VIM refining Ni-base superalloy using CaO crucible was studied. It was found that the desulphurization process could not be carried out by only using CaO crucible. The role of Al addition to desulphurization was also studied. Combining with the results of XRD and composition analysis of the CaO crucible, the mechanism of desulphurization was proposed. Thermodynamical calculation about the reaction between the interface of CaO crucible and liquid metal has been discussed. This work indicated that under proper refining technology the S content in the liquid Ni-base alloy could be reduced from 3×10-5 to 2×10-6-4×10-6.
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    Improving Densification and Mechanical Properties of FeAl/TiC Composites by Addition of Ni
    Yong LIU, Fengxiao LIU, Baiyun HUANG, Kechao ZHOU, Yuehui HE, Zhihong TANG
    J. Mater. Sci. Technol., 2003, 19 (01): 73-76. 
    Abstract   HTML   PDF (1176KB)
    FeAl/TiC composites were fabricated by hot pressing blended elemental powders. The effects of Ni-doping on the densification and mechanical properties of the composites were studied. Results show that the density of the composites decreases with the content of TiC increasing, and the addition of Ni significantly improves the densification process by enhancing mass transfer in the bonding phase. The mechanical properties of the composites are closely related with their porosity. Besides increasing the density of the composites, the addition of Ni improves the mechanical properties by other three effects: solution-strengthening the bonding phase, strengthening the FeAl-TiC interface and increasing ductile fracture in FeAl phase.
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    Optical Dispersion Parameters with Different Orientations for SrLaAlO4 Single Crystals
    Z.El-Gohary, M.El-Nahass, H.Soliman, Y.L.El-Kady
    J. Mater. Sci. Technol., 2003, 19 (01): 77-80. 
    Abstract   HTML   PDF (614KB)
    The different optical dispersion parameters of SrLaAlO4 single crystals have been studied by the transmission and reflection measurements at normal incidence for the three orientations 001, 100 and 101 in the spectral range 400nm-2500nm.The optical absorption data revealed the existance of allowed indirect and direct transition. The refractive index has abnormal behaviour in the spectral region 400-900nm, but has a normal one in the higher wavelength region. The optical dispersion parameters, the single oscillator energy Eo and the dispersion energy Ed were determined and indicated the ionic structure of the material. The high-frequency dielectric constant, the lattice dielectric constant and the electronic polarizability were determined by the free carriers and the lattice vibration modes. The real dielectric constant ε1 the dielectric loss tangent (tanδ), the volume (VELF) and the surface energy loss function (SELF) have also been discussed.
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    XRD and TEM Analysis in the Interface of Diffusion Bonding for Fe3Al/Q235 Dissimilar Materials
    Yajiang LI, Juan WANG, Huiqiang WU, Jicai FENG
    J. Mater. Sci. Technol., 2003, 19 (01): 81-84. 
    Abstract   HTML   PDF (822KB)
    Phase structure characteristics near the interface of Fe3Al/Q235 diffusion bonding are investigated by means of X ray diffraction (XRD), transmission electronic microscope (TEM) and electron diffraction, etc. The test results indicated that obviously a diffusion transition zone forms near the interface of Fe3Al/Q235 under the condition of heating temperature 1050-1100oC, holding time 60 min and pressure 9.8 MPa, which indicated that the diffusion interface of Fe3Al/Q235 was combined well. The diffusion transition zone consisted of Fe3Al and α-Fe(Al) solid solution. Microhardness near the diffusion transition zone was HM 480-540. There was not brittle phase of high hardness in the interface transition zone. This is favorable to enhance toughness of Fe3Al/Q235 diffusion joint.
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    Comparison on Mathematical Models for Description of Flow Curves of Stable Austenitic Steels
    Xing TIAN, Rujin TIAN
    J. Mater. Sci. Technol., 2003, 19 (01): 84-86. 
    Abstract   HTML   PDF (594KB)
    The flow curves were measured for the stable austenitic steels 304L and 304LN by means of tensile test at room temperature, which are described by the models σ=K1εn1+Exp(K2+n2ε),σ=Kεn1+n2lnε andσ=σo+Kεn (where, K1, K2, n1 and n2; K, n1 and n2; σo, K and n are constant). The comparison of the maximum deviations and the consideration of the variation of the work hardening rate with true strain show that the flow curves for the austenitic steels 304L and 304LN can be described by the model σ=Kεn1+n2lnε at higher recision. The derivatives of the models σ=Kεn1+exp(K2+n2ε) andσ=K1εn1+n2lnε with respect to true strain, exhibit the extreme at low true strain. This inherent character indicates that both models are unsuitable to describe the part of the work hardening rate curve at low true strain.
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    Effect of Superfine Slag Powder on HPC Properties
    Wu YAO, Jie LI
    J. Mater. Sci. Technol., 2003, 19 (01): 87-90. 
    Abstract   HTML   PDF (1502KB)
    A superfine slag powder (SP) made from granulated blast furnace slag incorporating activators by using special milling technique, was used as supplementary cementitious material in high performance concrete (HPC), replacing part of the mass of normal Portland cement. The effects of the SP on the workability, mechanical and crack self-healing properties of HPC were studied. The hydration process and microstructure characteristics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The crack self-healing capacity was evaluated by Brazilian test. The test results indicate that the SP has especially supplementary effect on water reducing and excellent property of better control of slump loss. The concrete flowability increases remarkably with the increase of SP replacement level in the range of 20% to 50%. The compressive and splitting tensile strengths of HPC containing SP are higher than the corresponding strength of the control concrete at all ages. The crack self-healing ability is highly dependent on SP content of HPC.
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    Effect of Stoichiometry on Properties of Rare-Earth-Based Hydrogen Storage Alloy for Nickel-Metal Hydride Secondary Battery
    Quan'an LI, Yungui CHEN, Mingjing TU
    J. Mater. Sci. Technol., 2003, 19 (01): 90-92. 
    Abstract   HTML   PDF (650KB)
    Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys Ml(Ni0.71Co0.15-Al0.06Mn0.08)x (Ml=Lanthanum-rich Michmetal, x=4.6-5.2) have been investigated. The lattice constants a, c and cell volumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x, the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateau pressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest discharge capacity and the best cycling stability among the studied alloys.
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    Synthesis of β-Sialon from Coal Gangue
    Xingyuan LUO, Jialin SUN, Chengji DENG, Yanruo HONG
    J. Mater. Sci. Technol., 2003, 19 (01): 93-96. 
    Abstract   HTML   PDF (913KB)
    It is worth to study the synthesis of β-Sialon from coal gangue, because coal gangue is a waste of coal production and is a high quality kaolin contained carbon which is a perfect raw material of contained reducer itself for synthesis of β-Sialon. The study showed that a high conversion rate of 95% from coal gangue to β-Sialon could be obtained by using process of carbothermal reduction nitridation when strictly controlled the thermodynamic conditions of synthesis. For controlling the synthesis conditions easy, the details of the effects of pco, po2 and T on the conversion rate of β-Sialon were discussed detailedly and the phase diagrams of oxygen pressure vs composition for Si3N4-AlN-Al2O3-SiO2 system at 1350, 1500, and 1600oC were constructed in the paper.
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    Analysis of Key Technologies and Equipments Development of Largescale Melted Extrusion Manufacturing Systems
    Lei ZHANG, Sheng CHEN, Yongnian YAN, Renji ZHANG
    J. Mater. Sci. Technol., 2003, 19 (01): 215-217. 
    Abstract   HTML   PDF (0KB)
    To develop large-scale RP systems used to producing functional parts and large-sized models has become an urgent call now. In this paper, a large-scale RP system, MEM600-I, based on the melted extrusion manufacturing (MEM) process has been developed successfully. And the key issues to develop such a system are discussed. Based on the actual forming experiment, it is concluded that the MEM600-I works reliably and the forming efficiency is much higher than its parallel equipments.
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