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ISSN 1005-0302
CN 21-1315/TG
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      28 November 2002, Volume 18 Issue 06 Previous Issue    Next Issue
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    Research Articles
    Formation of Liquid Pools Entrapped within Solid Grains of ZA27 Alloys during Partial Remelting
    Tijun CHEN, Yuan HAO, Jun SUN
    J. Mater. Sci. Technol., 2002, 18 (06): 481-483. 
    Abstract   HTML   PDF (439KB)
    The investigations were performed into the formation processes of liquid pools entrapped within solid grains of three ZA27 alloys, produced respectively by either grain refinement, or traditional permanent casting or mechanical stirring, during partial remelting at semisolid temperature of 460°C. The results show that the rapid coalescence of primary grains due to merging of secondary arms during the initial stage of partial remelting is the main cause for the formation of the entrapped liquid pools. This coalescence resulted in that a high quality of eutectics, especially the h phase, was entrapped within the grains, and then remelted to form liquid pools during the subsequent heating. In addition, the growth of the h phase decomposed from the primary a' phase and b phase and the subsequent remelting is another cause for the refined and permanent mould casting alloys. Furthermore, the agglomeration of the solid grains also resulted in the entrapment of liquid in the interior of grains.
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    Build Axial Gradient Field by Using Axial Magnetized Permanent Rings
    Quanling PENG
    J. Mater. Sci. Technol., 2002, 18 (06): 483-484. 
    Abstract   HTML   PDF (190KB)
    Axial magnetic field produced by an axial magnetized permanent ring was studied. For two permanent rings, if they are magnetized in the same directions, a nearly uniform axial field can be produced. If they are magnetized in opposite direction, an axial gradient magnetic field can be generated, with the field range changing from B0 to B0. A permanent magnet with a high axial gradient field was fabricated, the measured results agree with the PANDIRA calculation very well. For wider usage, it is desirable for the field gradient to be changed. Some methods to produce the variable gradient field are presented. These kinds of axial gradient magnetic field can also be used as a beam focusing for linear accelerator if the periodic field can be produced along the beam trajectory. The axial magnetic field is something like a solenoid, large stray field will leak to the outside environment if no method is taken to control them. In this paper, one method is illustrated to shield off the outside leakage field.
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    Superhard Nanocomposite Coatings
    Sam ZHANG, Deen SUN, Yongqing FU
    J. Mater. Sci. Technol., 2002, 18 (06): 485-491. 
    Abstract   HTML   PDF (1648KB)
    The recent development in the field of nanocomposite coatings with good mechanical properties is critically reviewed in this paper. The design principle and materials selection for the nanocomposite coatings are introduced. Different methods for the preparation of superhard nanocomposite coatings are described with emphasis on the magnetron sputtering. Based on recent theoretical and experimental results regarding the appearance of superhardness in nanocomposite coating, lattice parameter changes, crystallite size, microstructure and morphology are reviewed in detail. Also emphasized are the mechanical properties (especially on hardness) and the ways by which the properties are derived.
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    Electrical Resistance Measurement of Glass Transition and Crystallization Characteristics of Zr-Al-Cu-Ni Metallic Glasses
    Yaping WANG, Ke LU
    J. Mater. Sci. Technol., 2002, 18 (06): 492-496. 
    Abstract   HTML   PDF (428KB)
    In this paper, glass transition and thermal stability of the Zr-Al-Cu-Ni metallic glasses were investigated by using electrical resistance measurement (ERM), DSC and X-ray diffraction techniques. The experimental results show that the ERM is capable of detecting the glass transition of the amorphous alloys and can help to distinguish the crystallization products of the Zr-Al-Cu-Ni metallic glasses owing to the difference of the electrical resistivity between the precipitation phases.
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    An Explicit Function Expression for dc Bias and Temperature Dependence of Magnetoresistances in Magnetic Tunnel Junctions
    Xiufeng HAN
    J. Mater. Sci. Technol., 2002, 18 (06): 497-501. 
    Abstract   HTML   PDF (524KB)
    An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2) and the anisotropic-wavelength-cutoff energy ECγof spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/Ir22Mn78(12 nm)/Co75Fe25(4 nm)/Al(0.8 nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 (20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.
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    Analysis on Microstructure and Misorientation of Ultrathin Hot Strip of Low Carbon Steel Produced by Compact Strip Production
    Hao YU, Yonglin KANG, Jie FU
    J. Mater. Sci. Technol., 2002, 18 (06): 501-503. 
    Abstract   HTML   PDF (371KB)
    The microstructure and misorientation of ultrathin hot strip were analyzed by CSP technology using electron back scattered diffraction (EBSD) method and Autoforge finite element program. The experimental results showed that the finishing hot rolling microstructures were the mixture of recrystallized and deformed austenite. After phase transformation, ferrite grains embody substructures and dislocations, leading to the high strength and relatively low elongation rate of the ultrathin hot strip. The FEM simulation of strain mode and distribution in deformation area has been fulfilled. The simulation results are in good agreement with the theoretical analysis and experimental results.
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    Evolution of Thermoplastic Shear Localization and Related Microstructures in Al/SiCp Composites Under Dynamic Compression
    Yongbo XU, Zhong LING, Xin Wu, Yilong BAI
    J. Mater. Sci. Technol., 2002, 18 (06): 504-508. 
    Abstract   HTML   PDF (939KB)
    The localized shear deformation in the 2024 and 2124 Al matrix composites reinforced with SiC particles was investigated with a split Hopkinson pressure bar (SHPB) at a strain rate of about 2.0´103 s-1. The results showed that the occurrence of localized shear deformation is sensitive to the size of SiC particles. It was found that the critical strain, at which the shear localization occurs, strongly depends on the size and volume fraction of SiC particles. The smaller the particle size, the lower the critical strain required for the shear localization. TEM examinations revealed that Al/SiC p interfaces are the main sources of dislocations. The dislocation density near the interface was found to be high and it decreases with the distance from the particles. The Al matrix in shear bands was highly deformed and severely elongated at low angle boundaries. The Al/SiCp interfaces, particularly the sharp corners of SiC particles, provide the sites for microcrack initiation. Eventual fracture is caused by the growth and coalescence of microcracks along the shear bands. It is proposed that the distortion free equiaxed grains with low dislocation density observed in the center of shear band result from recrystallization during dynamic deformation.
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    Lattice Effects and Irreversible Magnetoresistance in Gd Doped La-Ca-Mn-O
    Baoxin HUANG, Yihua LIU, Ruzhen ZHANG, Chengjian WANG, Gang JI, Liangmo MEI
    J. Mater. Sci. Technol., 2002, 18 (06): 509-512. 
    Abstract   HTML   PDF (440KB)
    The Gd substituting effects for La in La0.67Ca0.33MnO3 has been studied. With increasing the substituting amount of Gd, the phase transition temperature of metal-isolator for the samples decreases, the corresponding peak resistivity increases,the Curie temperature decreases monotonically. The substitution of La-Ca-Mn-O with 11% Gd for La improved the magnetoresistance ratio by an order of magnitude. The effects of substituting Gd can be explained in terms of the lattice effects. An irreversible MR behaviour was observed in Gd-substituting compounds. This effect became marked when the substituting amount of Gd was greater than 7%. A maximum irreversible increment of MR ratio as large as 91% was obtained when Gd substituting amount was 11%.
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    Nature and Growth of Interaction Layers Formed during the Reaction between Solid Ni and Liquid Al
    Qiangang XU, Haifeng ZHANG, Bingzhe DING, Zhuangqi HU
    J. Mater. Sci. Technol., 2002, 18 (06): 512-515. 
    Abstract   HTML   PDF (605KB)
    The nature and growth of the interaction layers between solid Nb and liquid Al has been studied by carrying out the tests on Nb(s)-Al(l) and Nb(s)-Al(l)-Ni(s) reaction couples isothermally reacted between 700°C and 900°C for different time intervals. It has been found that the interaction layer between Nb and Al contains two parts: a thin continuous layer of NbAl3 adjacent to the Nb surface and a two-phase zone constituted of NbAl3 particles dispersed in an Al matrix. Although the nature and growth of interaction layers follows the four-stage mechanism, a typical cruciform pattern does not occur in Nb(s)-Al(l) reaction couples. However, a cruciform pattern was observed in Nb(s)-Al(l)-Ni(s) reaction couples. The movement of NbAl3 particles is important to the production of cruciform pattern in the reaction couples.
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    Texture Evolutions in Fe-6.5%Si Produced by Rapid
    Liang ZUO, Guangyong HU, Yuhui SHA, Claude ESLING
    J. Mater. Sci. Technol., 2002, 18 (06): 516-518. 
    Abstract   HTML   PDF (315KB)
    Fe-Si ribbons and thin sheets with 6.5%Si content were prepared by means of the single roller rapid solidification and chemical vapor deposition (CVD), respectively. The initial textures of rapidly solidified Fe-6.5%Si ribbons were characteristic of the {100} fiber-type, which became weakened during primary recrystallization in various atmospheres. At the stage of secondary recrystallization, the {100} texture formed in Ar and the {110} texture in hydrogen, while there occurred a texture transformation from the{100} type to the{110} type in vacuum with the increase of annealing temperature. For Fe-6.5%Si sheets prepared by Si deposition in old-rolled Fe-3%Si matrix sheets, their textures were dominated by the h-fiber (<001>//RD) with the maximum density at he {120}<001> orientations. After homogenization annealing, the h-fiber could evolve into the {130}<001> type or become more concentrated on the {120}<001> orientations, depending on the cold rolling modes of Fe-3%Si matrix sheets.
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    Through Thickness Variation of Cross Shear Rolling Texture in Grain Oriented Silicon Steel
    Gang LIU, Liang ZUO, Fu WANG, Xiang ZHAO, Zhide LIANG
    J. Mater. Sci. Technol., 2002, 18 (06): 519-521. 
    Abstract   HTML   PDF (278KB)
    The texture inhomogeneity in cross shear rolled grain oriented Si steel was investigated by means of the through thickness texture analysis. For the chosen rolling reductions (55%, 66.5%) and mismatch speed ratios (1.0, 1.1, 1.3), the deformation textures in various thickness layers consist of three major components, i.e. strong g-fiber, medium a-fiber and weak h-fiber, and they show an asymmetrical distribution throughout the thickness. The effect of reduction on the texture gradient is found to be more significant at and near the center layer; however, the effect of mismatch speed ratio is less important. In most cases, a strong {111}<112> texture component appears in the subsurface layers, that may favour the formation of a sharp Goss texture during the subsequent annealing.
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    Static Adsorption of Xenon on ACF at 257 K
    Haitao ZHANG, Yalong WANG, Xuhui WANG, Lixing ZHANG, Liyun CHEN
    J. Mater. Sci. Technol., 2002, 18 (06): 522-526. 
    Abstract   HTML   PDF (560KB)
    The static adsorption of xenon on active carbon fiber (ACF) at 257 K was measured with ASAP2010 specific surface area and pore diameter distribution instrument by changing the working gas from nitrogen to xenon. Compared with grain activated carbon (GAC), the results were as follows: (1) The adsorption performance of Viscose-based ACF (VACF-AS) was the best among all absorbents tested. VACF-A3 was the superior xenon absorbent. The performance of pitch-based ACF (PACF-CS) approached that of GAC, (2) Due to the difference of aperture distribution, the adsorption performances of ACF with different radics were different under the same experiment conditions even though the specific surface area was similar, (3) There were some differences of adsorptive capacity among ACF absorbents which had the same radic, however there was not definite relationship between their specific surface area and adsorptive capacity, (4) The adsorption of xenon on all kinds of ACF agrees with Langmuir equation, (5) The adsorptive curves can be fitted with a binomial equation.
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    New Developed Welding Electrode for Improving the Fatigue Strength of Welded Joints
    Wenxian WANG, Lixing HUO, Yufeng ZHANG, Dongpo WANG, Hongyang JING
    J. Mater. Sci. Technol., 2002, 18 (06): 527-531. 
    Abstract   HTML   PDF (455KB)
    A new welding electrode, low transformation temperature electrode (LTTE), was introduced in this paper. It was described in design principle, mechanics, chemical compositions of their deposited metal and manufacturing methods. It was proved that the best transformation starting temperature from austenite to martensite of the deposited metal of LTTE was at about 191°C and it was obtained by adding alloying elements such as Cr, Ni, Mn and Mo. The microstructure of the weld metal of the LTTE was low carbon martensite and residual austenite. The compressive residual stress was induced around the weld of the LTTE and the –145 MPa in compression could be obtained in middle of weld metal. The fatigue tests showed that the fatigue strength of the longitudinal welded joints welded with the LTTE at 2´106 cycles was improved by 59% compared with that of the same type of welded joints welded with conventional E5015 and the fatigue life was increased by 47 times at 162 MPa. It is a very valuable method to improve the fatigue performance of welded joints.
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    A Study of the Ni-Cr-Zr System at 900°C
    Ximiao PAN, Zhanpeng JIN
    J. Mater. Sci. Technol., 2002, 18 (06): 532-534. 
    Abstract   HTML   PDF (300KB)
    The phase equilibrium relations of the ternary Ni-Cr-Zr system at 900°C have been investigated by means of diffusion triple and electron probe microanalysis (EMPA) techniques. A series of tie lines and triangles have been determined, and the corresponding tentative isothermal section is presented based on the current information.
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    Deposition of Bioactive Layer on NiTi Alloy by Chemical Treatment
    Ya LIU, Xianjin YANG, Minfang CHEN, Shengli ZHU, Zhenduo CUI
    J. Mater. Sci. Technol., 2002, 18 (06): 534-537. 
    Abstract   HTML   PDF (497KB)
    A simple chemical method was developed for inducing bioactivity on NiTi alloys (50 at. pct by Ni/Ti). A layer of calcium phosphate was deposited on the surface to improve biocompatibility of the alloy. NiTi alloys were first etched in HNO3 aqueous solution, and then treated with boiling diluted NaOH solution. A rough surface was created and a thin TiO2 layer was formed on the surface. Pre-calcification was then introduced by immersing the treated NiTi alloys in supersaturated Na2HPO4 solution and supersaturated Ca(OH)2 solution in turn before calcification in simulated body fluid (SBF). A dense and uniform bonelike calcium phosphate (Ca-P) bioactive layer was formed on the surfaces of the specimen, which would improve their biocompatibility. Morphology and element analysis on NiTi surfaces during the treatments were investigated in detail by means of environment scanning electron microscopy (ESEM), energy dispersion X-ray spectroscopy (EDXS), and X-ray diffraction (XRD).
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    Thermodynamic Analysis on Relation Between T0 and sM in a Ti44Ni47Nb9 Shape Memory Alloy
    Wei JIN, Mingzhou CAO, Rui YANG, Zhuangqi HU, Shaoyu QIU, Hong ZOU
    J. Mater. Sci. Technol., 2002, 18 (06): 538-540. 
    Abstract   HTML   PDF (272KB)
    The effect of heat treatment on martensitic transformation behavior has been investigated in Ti44Ni47Nb9 alloy. The relation between transformation temperatures and critical stress of stress induced martensitic transformation is interpreted in terms of thermodynamic theory. It is shown that the decrease in transformation temperature in specimens of slow cooling rate or low temperature aging after solution heat treatment results from the changes of Ni/Ti ratio in the matrix. The increase of critical stress of stress induced martensitic transformation is a consequence of the decrease of transformation temperatures.
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    Al2O3-Coated Nano-SiC Particles Reinforced Al2O3 Matrix Composites
    Juxian ZHANG, Jinjun FENG, Longqiao GAO
    J. Mater. Sci. Technol., 2002, 18 (06): 541-543. 
    Abstract   HTML   PDF (366KB)
    Properties of Al2O3-coated nano-SiC have been compared with those of as-received SiC. The isoelectric point (IEP) of SiC changed from pH3.4 to pH7.3 after coating with the alumina precursor, which is close to that of alumina. Because both surfaces of coated SiC and Al2O3 possess higher positive charge at pH=4.5~5.0, they are uniformly dispersed in the two-phase aqueous suspensions, Then a mixed powder containing nano-SiC dispersed homogeneously into the Al2O3 matrix was achieved from flocculating the two-phase suspension. Finally, Al2O3/SiC nanocomposites were obtained by coating nano-SiC with Al2O3, in which the majority of SiC particles were located within the Al2O3 grains. The observation by transmission electron microscopy (TEM) and the analysis by the X-ray photoelectron spectroscopy (XPS) showed that cracks propagated towards the intragranular SiC rather than along grain boundaries.
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    Powder Forging of a Motorcycle Connecting Rod
    Guangchun WANG, Guoqun ZHAO
    J. Mater. Sci. Technol., 2002, 18 (06): 544-548. 
    Abstract   HTML   PDF (455KB)
    A motorcycle connecting rod is one of the major moving parts affecting the engine performance. The traditional manufacturing process results in material waste and excessive machining. A new method of hot forging P/M has been proposed and studied experimentally. In order to achieve uniform density, the punch was divided into three parts to consolidate the loose powder. The multistage movement of the three parts of the punch, called synchronous compaction, results in the desired uniform density. Powder flow during consolidation was illustrated and the density distribution of the compacts was measured. A set of forging dies with flash was used to produce densification and deformation of the sintered compact. Then a set of flashless forging dies was designed to obtain the desired shape and dimensions of the connecting rod. The effects of forging temperature and initial compact density on densification were evaluated through hot forging experiments. Based on properties achieved, Fe-C-Cu-Mo was selected as the alloy powder. Through testing and metallographic observation the physical and mechanical properties of the connecting rod produced by the P/M hot forging were found to be superior to those manufactured by the traditional method.
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    Corrosion Behaviours of Copper Alloy in Solutions Containing Na2SO4 and NaCl with Different Concentrations
    A.A.El-Meligi
    J. Mater. Sci. Technol., 2002, 18 (06): 549-551. 
    Abstract   HTML   PDF (330KB)
    Potentiodynamic polarisation, potential-time measurements, X-ray diffraction (XRD) and infrared spectroscopy (IR) have been used to investigate the effect of different concentrations of Na2SO4 in the absence and presence of NaCl, on the corrosion of Cu-alloy. The electrochemical measurements showed that the increase of Na2SO4 concentration led to increase the corrosion current density of Cu alloy and vice versa. The presence of NaCl shifted the potential to more cathodic potential, which had a great influence on the protectiveness of the Cu oxide layer formed on the surface in presence of Na2SO4. The spectrometric measurements indicated the constituents of the film formed on the alloy surface were mainly Cu2O, in addition to the oxides, NiO and Fe2O3, which were traced by XRD analysis.
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    Influence of NaCl Deposition on Atmospheric Corrosion of A3 Steel
    Qing QU, Chuanwei YAN, Lei ZHANG, Ye WAN, Chunan CAO
    J. Mater. Sci. Technol., 2002, 18 (06): 552-555. 
    Abstract   HTML   PDF (413KB)
    Regularity of the initial atmospheric corrosion of A3 steel in the presence of NaCl was investigated. The results showed that NaCl can accelerate the corrosion of A3 steel. Dry mass gain of A3 steel in the presence of NaCl deposition increases with the exposure time, which can be correlated by using exponential decay function. The relationship between dry mass gain and amount of NaCl deposition at a certain exposure time follows a quadratic function. More amount of NaCl deposition will slow down the corrosion rate to some extent after exposure for a certain time. SEM/EDAX was used to characterize the corrosion surface and products. The surfaces of the NaCl treated A3 steel were obviously uneven, and some tiny crevices appear in the corrosion products that could help O2 transmit to the inner layer. The amount of oxygen in atomic percentage in the corrosion products increases with the amount of NaCl deposition.
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    Effect of Phosphorus on Microstructure and High Temperature Properties of a Cast Ni-base Superalloy
    Chao YUAN, Fengshi YIN, Xiaofeng SUN, Hengrong GUAN, Zhuangqi HU
    J. Mater. Sci. Technol., 2002, 18 (06): 555-557. 
    Abstract   HTML   PDF (278KB)
    Effect of phosphorus on the microstructure and high temperature properties of a cast Ni-base superalloy M963 has been investigated. SEM observation and EDS analysis showed that P was mostly enriched in the interdendritic region, and the P-rich phase was formed in the front position of finally solidified eutectics in high P doped alloys. It was found that the P-rich phase, as preferred initiation and propagation site of cracks, could aggravate the fracture process at high temperature in high P doped alloys.Consequently, high P addition would reduce remarkably the ductility and creep life of M963 superalloy at high temperature.
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    Preparation and Photochromic Properties of Hybrid Thin Films Based on Heteropolyoxometallate and Polyacrylamide
    Wei FENG, Tierui ZHANG, Yan LIU, Ran LU, Cheng GUAN, Yingying ZHAO, Jiannian YAO
    J. Mater. Sci. Technol., 2002, 18 (06): 558-560. 
    Abstract   HTML   PDF (314KB)
    A series of photochromic hybrid films were prepared through entrapping Dawson type tungsten heteropolyoxometallates (P2W18O626-) and molybdenum heteropolyoxometallate (P2Mo18O626-) into polyacrylamide matrix. FTIR results showed that the Dawson geometry of heteropolyoxometallates is still preserved inside the composites and strong coulombic interaction is built between heteropolyoxometallates and polyacrylamide via hydrogen bonding. Irradiated with ultraviolet light, the transparent films change from colorless to blue and show reversible photochromism. The bleaching process occurs when the films are in contact with air or O2 in the dark. The molybdenum heteropolyoxometallate hybrid film has higher photochromic efficiency and slower bleaching reaction than tungsten heteropolyoxometallate hybrid film. ESR results indicated that polyacrylamide is a hydrogen donor and the photoreduced process is in accordance with the radical mechanism.
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    Phase Behavior, Thermal Stability and Rheological Properties of PPEK/PC Blends
    Gongxiong LIAO, Xigao JIAN, Jinyan WANG
    J. Mater. Sci. Technol., 2002, 18 (06): 561-563. 
    Abstract   HTML   PDF (1439KB)
    Phase behavior, thermal stability and rheological properties of the blends of poly(phthalazinone ether ketone) (PPEK) with bisphenol-A polycarbonate (PC) prepared by solution coprecipitation were studied using differential scanning calorimetry (DSC),Frourier-Transform IR spectroscopy (FT-IR), thermogravimetric analysis (TGA) and capillary rheometer. The DSC results indicated that PPEK/PC blends are almost immiscible in full compositions.FT-IR investigation showed that there were no apparent specific interactions between the constituent polymers. The blends keep excellent thermal stability and the addition of PC degrades the thermal stability of blends to some degree. The thermal degradation processes of the blends are much similar to that of PC. The studies on rheological properties of blends show that blending PPEK with PC is beneficial to reducing the melt viscosity and improving the appearance of PPEK.
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    Effects of Nitridation on Properties of SiC Fiber and Interface of Ti Matrix Composite
    Nanlin SHI, Jiwei FENG, Yanfen GUO, Yuyin LIU, Z.X.Guo
    J. Mater. Sci. Technol., 2002, 18 (06): 563-565. 
    Abstract   HTML   PDF (1237KB)
    Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.
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    Gaseous Nitriding Process of Surface Nanocrystallized (SNCed) Steel
    Duohui BEI, Jianfeng GU, Jiansheng PAN, Jian Leür, Ke LU
    J. Mater. Sci. Technol., 2002, 18 (06): 566-568. 
    Abstract   HTML   PDF (285KB)
    The behavior of gaseous nitriding on the surface nanocrystallized (SNCed) steel was investigated.The mild steel discs were SNCed on one side by using the method of ultrasonic shot peening. The opposite side of the discs maintained the original coarse-grained condition. The gaseous nitriding was subsequently carried out at three different temperatures: 460,500 and 560°C. The compound layer growth and diffusion behavior were then studied. It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate. As a result, nitriding time could be reduced to the half.It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.
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    Development of Novel Binder for Hardmetal Powder Extrusion Molding
    Jicheng ZHOU, Baiyun HUANG
    J. Mater. Sci. Technol., 2002, 18 (06): 569-571. 
    Abstract   HTML   PDF (402KB)
    A novel binder system for hardmetal powder extrusion moulding (PEM) process has been developed. The binder system comprises a major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction of very finely dispersed polymer. The feedstocks are mixed as a thick slurry at a suitable temperature and are rapidly homogenized by stirring at an adequate shear force. The binders are removed by thermal debinding. The thermal debinding mechanism has been investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). At the first stage of debinding, the LMWCs are removed. These open up pore channels which allows much faster removal of the remaining polymer component during the subsequent stage. The microstructures of the moulded green parts were observed by scanning electron microscopy (SEM). The debound samples were sintered at different temperatures, and the sintered samples properties were measured.
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    RP-based Abrading Technique for Graphite EDM Electrode
    Yiping TANG, Hongzhi ZHOU, Jun HONG, Bingheng LU
    J. Mater. Sci. Technol., 2002, 18 (06): 572-574. 
    Abstract   HTML   PDF (311KB)
    Traditional processes for machining mold cavities are lengthy and costly. EDM (electro-discharge machining) is the most commonly used technique to obtain complex mold cavities. However, some electrodes are difficult to fabricate because of the complexity. Applying RP (rapid prototyping) technology to fabricate an abrading tool which is used to abrade graphite EDM electrodes, the cost and cycle time can greatly be reduced. The paper describes the work being conducted in this area by the authors. This technique will find widespread application in rapid steel mold manufacturing.
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    Effect of Incomplete Thermal Cycle on Transformation Behavior of Deformed TiNi Thin Film
    Xiaopeng LIU, Wei JIN, Mingzhou CAO, Dazhi YANG, Feixia CHEN
    J. Mater. Sci. Technol., 2002, 18 (06): 575-576. 
    Abstract   HTML   PDF (217KB)
    Compared with the undeformed TiNi film, the martensite-austenite transformation (M-A) of the deformed one is elevated to a higher temperature on the first heating, but it nearly returns back to the original temperature on the second heating. An incomplete M-A transformation of the deformed TiNi film on the first heating divides the total martensite population into the self-accommodating martensite M2 and the oriented martensite M1. Thus, two transformations corresponding to M1-A and M2-A transition occur on the second heating. However, the forward transformation is not affected by the incomplete thermal cycle.
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