Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      28 November 2008, Volume 24 Issue 06 Previous Issue    Next Issue
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    Research Articles
    Microstructural Characterization of the Shear Bands in Fe-Cr-Ni Single Crystal by EBSD
    Huajie YANG, J.H.Zhang, Yongbo XU, Marc , re′ Meyers
    J. Mater. Sci. Technol., 2008, 24 (06): 819-828. 
    Abstract   HTML   PDF (5532KB)

    An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate (≈104 s-1) deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM (electron backscat-ter diffraction-scanning electron microscopy), TEM (transmission electron in microscopy) and HREM (high-resolution electron microscopy). The results reveal that the propagation of the shear band exhibits an asymmet-rical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistanceto the collapse in different crystallographic directions; The γ–ε–α′ phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2 μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×106 s-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.

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    A Phase-field Model to Simulate Recrystallization in an AZ31 Mg Alloy in Comparison of Experimental Data
    Mingtao WANG, B.Y.Zong, Gang WANG
    J. Mater. Sci. Technol., 2008, 24 (06): 829-834. 
    Abstract   HTML   PDF (2136KB)
    A model has been established to simulate the realistic spatio-temporal microstructure evolution in recrystallization of a magnesium alloy using the phase field approach. A set of rules have been proposed to decide the real physical value of all parameters in the model. The thermodynamic software THERMOCALC is applied to determine the local chemical free energy and strain energy, which is added to the free energy density of grains before recrystallization. The Arrhenius formula is used to describe boundary mobility and the activity energy is suggested with a value of zinc segregation energy at the boundary. However, the mobility constant in the formula was found out by fitting to a group of grain size measurements during recrystallization of the alloy. The boundary range is suggested to decide the gradient parameters in addition of fitting to the experimental boundary energy value. These parameter values can be regarded as a database for other similar simulations and the fitting rules can also be applied to build up databases for any other alloy systems. The simulated results show a good agreement with reported experimental measurement of the alloy at the temperatures from 300 to 400℃ for up to 100 min but not at 250℃. This implies a mechanism variation in activity energy of the boundary mobility in the alloy at low temperature.
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    Fractal Characteristics and Prediction of Ti-15-3 Alloy Recrystallized Microstructure
    Ping LI, Qing ZHANG, Kemin XUE
    J. Mater. Sci. Technol., 2008, 24 (06): 835-839. 
    Abstract   HTML   PDF (890KB)
    Grain shape of the hot deforming alloy is an important index to character the microstructure and performance of material. The fractal theory was applied to analyze the recrystallized microstructure of Ti-15-3 alloy after hot deformation and solution treatment. The fractal dimensions of recrystallized grains were calculated by slit island method. The influence of processing parameters on fractal dimension and grain size was studied. It has been shown that the shapes of recrystallized grain boundaries are self-similar, and the fractal dimension varies from 1 to 2. With increasing deformation degree and strain rate or decreasing deformation temperature, the fractal dimension of grain boundaries increased and the grain size decreased. So the fractal dimension could characterize the grain shape and size. A neural network model was trained to predict the fractal dimension of recrystallized microstructure and the result is in excellent agreement with the experimental data.
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    Comparison between the Methods of Determining the Critical Stress for Initiation of Dynamic Recrystallization in 316 Stainless Steel
    M.Jafari, A.Najafizadeh
    J. Mater. Sci. Technol., 2008, 24 (06): 840-844. 
    Abstract   HTML   PDF (903KB)
    Several methods have been proposed to calculate the critical stress for initiation of dynamic recrystallization (σc) on the basis of mathematical methods. One of them is proposed by Stewart et al. in which this critical point appears as a distinct minimum in the (-dθ/dσ vs σ) through differentiating from θ vs σ. Another one is presented by Najafizadeh and Jonas by modifying the Poliak and Jonas method. According to this method, the strain hardening rate was plotted against flow stress, and the value of σc was attained numerically from the coefficients of the third-order equation that was the best fit from the experimental θ-σ data. Hot compression tests were used in the range of 1000 to 1100℃ with strain rates of 0.01–1 s-1 and strain of 1 on 316 stainless steel. The result shows that Najafizadeh and Jonas method is simpler than the previous one, and has a good agreement with microstructures. Furthermore, the value of normalized critical stress for this steel was obtained μc=σc/σp=0.92.
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    Preparation of Electrode Array by Electrochemical Etching Based on FEM
    Minghuan WANG, Di ZHU, Lei WANG
    J. Mater. Sci. Technol., 2008, 24 (06): 845-849. 
    Abstract   HTML   PDF (1365KB)
    Process technology of multiple cylindrical micro-pins by wire-electrical discharge machining (wire-EDM) and electrochemical etching was presented. A row of rectangular micro-columns were machined by wire-EDM and then machined into cylindrical shape by electrochemical etching. However, the shape of the multiple electrodes and the consistent sizes of the electrodes row are not easy to be controlled. In the electrochemical process, the shape of the cathode electrode determines the current density distribution on the anode and so the forming of multiple electrodes. This paper proposes a finite element method (FEM) to accurately optimize the electrode profile. The microelectrodes row with uniformity diameters with size from hundreds micrometers to several decades could be fabricated, and mathematical model controlling the shape and diameter of multiple microelectrodes was provided. Furthermore, a good agreement between experimental and theoretical results was confirmed.
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    Electrochemical Fabrication of Pd-Ag Alloy Nanowire Arrays in Anodic Alumina Oxide Template
    Erhong YUE, Gang YU, Yuejun OUYANG, Baicheng WENG, Weiwei SI, Liyuan YE
    J. Mater. Sci. Technol., 2008, 24 (06): 850-856. 
    Abstract   HTML   PDF (4267KB)
    The synthesis of Pd-Ag alloy nanowires in nanopores of porous anodic aluminum oxide (AAO) template by electrochemical deposition technique was reported. Pd-Ag alloy nanowires with 16%–25% Ag content are expected to serve as candidates of useful nanomaterials for the hydrogen sensors. Scanning electron microscopy (SEM) and energy dispersed X-ray spectroscopy (EDX) were employed to characterize the morphologies and compositions of the Pd-Ag nanowires. X-ray diffraction (XRD) was used to characterize the phase properties of the Pd-Ag nanowires. Pd-Ag alloy nanowire arrays with 17.28%–23.76% Ag content have been successfully fabricated by applying potentials ranging from -0.8 to -1.0 V (vs SCE). The sizes of the alloy nanowires are in agreement with the diameter of AAO nanopores. The underpotential deposition of Ag+ on Pd and Au plays an important role in producing an exceptionally high Ag content in the alloy. Alloy compositions can still be controlled by adjusting the ion concentration ratio of Pd2+ and Ag+ and the electrodeposition processes. XRD shows that nanowires obtained are in the form of alloy of Pd and Ag.
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    Novel Nanostructured MnO2 Prepared by Pulse Electrodeposition: Characterization and Electrokinetics
    H.Adelkhani, M.Ghaemi, S.M.Jafari
    J. Mater. Sci. Technol., 2008, 24 (06): 857-862. 
    Abstract   HTML   PDF (1847KB)
    Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample (pcMD) were carried out by different techniques: Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, Raman spectroscopy, and atomic force microscopy (AFM). SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current (dcMD). Higher distortion of MnO6 octahedral environment of dcMD was detected by FTIR and Raman spectroscopy. Cyclic voltammetric (CV) measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.
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    Preparation of AgCl Nano-Crystal Embedded Tellurite Nonlinear Optical Glasses under Electric Field Accompanied Heat Treatment
    Jian LIN, Wenhai HUANG, Bofang LI, Chong JIN, Changcheng LIU, Shuhua LEI
    J. Mater. Sci. Technol., 2008, 24 (06): 863-866. 
    Abstract   HTML   PDF (1557KB)
    The quantum effect of nano-crystals is an important factor to improve nonlinear optical performance of nano-crystal embedded glasses, while controlling the size distribution and content of nano-crystals in the glass accurately is a key to obtain good quality. The auxiliary direct current electric field, accompanied with heat treatment, was applied on AgCl containing niobic tellurite glass sheet. The nucleation and crystallization of the glass were well controlled under auxiliary electric field. It was found that the average size of AgCl nano-crystal particles in the glass is smaller than that under single heat treatment, and the content of nano-crystals is higher. Therefore the third-order nonlinear optical performance of the glass was increased a lot. The local-area distributed AgCl nano-crystal particles can also be embedded into a glass sheet by using locally applied electric field.
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    Effect of Zn, Cu, Cr and Pb Chlorides on the Formation of Tricalcium Aluminate Trisulfate Hydrate
    Wafaa S.Hegazi, Eisa E.Hekal, Essam A.Kishar, Maha R.Mohammed
    J. Mater. Sci. Technol., 2008, 24 (06): 867-872. 
    Abstract   HTML   PDF (2463KB)
    The effect of addition of Zn, Cu, Pb and Cr chlorides as admixtures on the hydration reaction of the system 3CaO•Al2O3-gypsum with molar ratio 1:3 was studied. Different ratios of each salt were used, namely 0.5%, 2% and 4% by weight of the solid mixture. Hydration reaction was carried out at 35℃ for various time intervals from 0.5 h to up to 7 d. Hydration rate of the system 3CaO•Al2O3-CaSO4•2H2O in absence and presence of different salts was studied via the determination of the combined water contents. X-ray diffraction analysis showed that the ettringite was the only hydration product formed in the different mixes. The hydration products were investigated by scanning electron microscopy (SEM) and thermal gravimetric analysis. The results indicated that the rate of formation of ettringite and its microstructure depend on the admixture and its dosage.
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    Alumina Effect on the Phase Transformation of 3Y-TZP Ceramics
    Ezzat S.Elshazly, M.El-Sayed Ali, S.M.El-Hout
    J. Mater. Sci. Technol., 2008, 24 (06): 873-877. 
    Abstract   HTML   PDF (936KB)
    The isothermal tetragonal-to-monoclinic phase transformation of 3 mol fraction Y2O3–ZrO2 ceramics containing different amounts of Al2O3 during ageing in water at 130℃ for periods of time up to 40 h was investigated to explore the effect of Al2O3 addition on this transformation. The propagation of the transformation into the specimen interiors was suppressed by the addition of Al2O3. The transformation kinetics showed a nucleation and growth mechanism on the specimen surface to be dominant in the low temperature ageing in water environment.
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    Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics
    Chunfeng LIU, Feng YE, Yu ZHOU, Yongliang WANG, Jiancun RAO
    J. Mater. Sci. Technol., 2008, 24 (06): 878-882. 
    Abstract   HTML   PDF (939KB)
    Densified Yb-, Y-, Dy-, Sm- and Nd-α-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations (Yb3+, Y3+ and Dy3+) are fully composed of α-Sialon, while in the larger cations (Sm3+ and Nd3+) doped ceramics also exist a few intergranular phase M′ (Re2Si3-xAlxO3+xN4-x) in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa•m1/2.
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    Oxidation of a Co-base Superalloy
    Guichen HOU, Zhiyuan LIU, Hua WEI, Qi ZHENG, Xiaofeng SUN, Hengrong GUAN, Zhuangqi HU
    J. Mater. Sci. Technol., 2008, 24 (06): 883-890. 
    Abstract   HTML   PDF (7997KB)
    The oxidation behavior of a cast polycrystalline Co-base superalloy was studied at temperatures from 900 to 1050℃ and analyzed by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that a cast Co-base superalloy follows the subparabolic oxidation kinetics at 900 and 1000℃, which are controlled by the growth of the inner Cr-rich layer, and that after oxidation at 1050℃ for 200 h, it almost exhibits the linear oxidation kinetics possible due to the volatility of Cr-rich oxide. A mixed scale forms on the alloy after prolonged oxidation. The oxide scale formed at 900 and 1000℃ is composed of an outer layer of spinel and an inner continuous Cr-rich layer and at 1050℃ is composed of a very discontinuous Cr-rich layer.
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    Influence of Metallic Substitutions on the Optical and Mechanical Properties of NLO Benzoyl Glycine Crystals
    T.Kishore Kumar, S.Janarthanan, S.M.Ravikumar, S.P, i, M.Vimalan, P.Sagayaraj, D.Prem An
    J. Mater. Sci. Technol., 2008, 24 (06): 891-894. 
    Abstract   HTML   PDF (1339KB)
    Benzoyl glycine (BG) is a promising organic nonlinear optical (NLO) crystal, whose second harmonic generation (SHG) efficiency is much higher than that of KDP (potassium dihydrogen phosphate). Single crystals of pure, Cu2+ and Cd2+ doped BG were grown by slow evaporation technique. Optically transparent and defect free single crystals of size up to 10 mm×15 mm×10 mm were harvested in a period of 40–60 days. The growth conditions of pure and doped crystals of BG were optimized and the grown crystals were confirmed by single crystal XRD (X-ray diffraction). The grown crystals were characterized by FTIR (Fourier transform infrared spectroscopy), optical absorption and microhardness studies. The microhardness studies confirm that BG has a moderate VHN (Vickers hardness number) value in comparison to the other organic NLO crystals. The efficiency of frequency doubling was measured for the using Nd:YAG laser and the results were discussed.
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    Electric Current-induced Failure of 200-nm-thick Gold Interconnects
    Bin ZHANG, Qingyuan YU, Jun TAN, Guangping ZHANG
    J. Mater. Sci. Technol., 2008, 24 (06): 895-898. 
    Abstract   HTML   PDF (852KB)
    200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The failure behavior of the Au interconnects under three kinds of electric currents were characterized in-situ by scanning electron microscopy. It is found that the formation of voids and subsequent growth perpendicular to the interconnect direction is the fatal failure mode for all the Au interconnects under three kinds of electric currents. The failure mechanism of the ultrathin metal lines induced by the electric currents was analyzed.
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    High Quality YBCO Film Growth on SrTiO3-Buffered LaAlO3 Substrate by Full Solution Method
    Sansheng WANG, Lin WANG, Bingfu GU
    J. Mater. Sci. Technol., 2008, 24 (06): 899-902. 
    Abstract   HTML   PDF (510KB)
    A full solution method has been developed as a low cost process of YBa2Cu3O7-x (YBCO) coated conductor fabrication. In this study, highly biaxially textured SrTiO3 (STO) buffer layers were fabricated on LaAlO3 (LAO) single crystal substrates by sol-gel method using metal alkoxides as the staring precursor materials. High quality YBCO superconducting film was then fabricated on STO-buffered LAO substrate by trifluoroacetic metalorganic deposition (TFA-MOD) method. For the YBCO superconducting film, only (00l) diffraction peaks can be detected by XRD (X-ray diffraction) analysis with no other phases detectable. Especially, In-plane texture of YBCO film is improved compared to that of STO buffer layer from phi scans analysis, which indicates the self-epitaxy phenomenon explained by considering interfacial energy. STO and YBCO films both show c-axis oriented grains growth and have uniform surface microstructure. A critical transition temperature, Tc (R=0) of 89.5 K and a critical current density of 2 mA/cm2 (77 K, self-field) were obtained for a 0.2 μm thick YBCO film on STO-buffered LAO substrate. No reaction between YBCO and STO was detected by XRD analysis. This full solution process may provide a promising low cost fabrication route for YBCO coated conductors on metal tape.
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    A Novel TiNi/AlSi Composite with High Strength and High Damping Capacity
    Shuwei LIU, Xiuyan LI, Desheng YAN, Haichang JIANG, Lijian RONG
    J. Mater. Sci. Technol., 2008, 24 (06): 903-906. 
    Abstract   HTML   PDF (485KB)
    A novel TiNi/AlSi composite with high compressive strength and high damping capacity was obtained by infiltrating Al-12%Si alloy into porous TiNi alloy. It had been found that the high compressive strength (440 MPa) of TiNi/AlSi composite is due to the increase of effective carrying area after infiltrating Al-12%Si alloy, while the high damping capacity is contributed to TiNi carcass, Al-12%Si filling material and micro-slipping at the interface.
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    Effect of Traverse/Rotational Speed on Material Deformations and Temperature Distributions in Friction Stir Welding
    Zhao ZHANG, Jun BIE, Yali LIU, Hongwu ZHANG
    J. Mater. Sci. Technol., 2008, 24 (06): 907-914. 
    Abstract   HTML   PDF (8342KB)
    A fully coupled thermo-mechanical model was developed to study the temperature fields and the plastic deformations of alloy AL6061-T6 under different process parameters during the friction stir welding (FSW) process. Three-dimensional results under different process parameters were presented. Results indicate that the maximum temperature is lower than the melting point of the welding material. The higher temperature gradient occurs in the leading side of the workpiece. The calculated temperature field can be fitted well with the one from the experimental test. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface, which is formed by the specific material flow patterns in FSW. The maximum temperature can be increased with increasing the welding speed and the angular velocity in the current numerical modelling.
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    Electrochemical Deposition and Nucleation of Aluminum on Tungsten in Aluminum Chloride-Sodium Chloride Melts
    Zhaowen WANG, Hongmin KAN, Zhongning SHI, Bingliang GAO, Yungang BAN, Xianwei HU
    J. Mater. Sci. Technol., 2008, 24 (06): 915-920. 
    Abstract   HTML   PDF (537KB)
    Electrochemical deposition and nucleation of aluminum on tungsten electrode from AlCl3-NaCl melts were studied by cyclic voltammetry, chronopotentiometry and chronoamperometry. Cyclic voltammetry and chronopo-tentiometry analyses showed that Al (III) was reduced at 200℃ in two consecutive steps in an electrolyte of molten AlCl3-NaCl system with a composition 52:48 molar ratio. The current-time characteristics of nucleation aluminum on tungsten showed a strong dependence on overpotentials. Chronoamperometry showed that the deposition process of aluminum on tungsten was controlled by an instantaneous nucleation with a hemispherical diffusion-controlled growth mechanism. The results could lead to a better understanding of the AlCl3-NaCl melt system that has technological importance in electrodeposition of metals as well as in rechargeable batteries.
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    Influences of Ag and Au Additions on Structure and Tensile Strength of Sn-5Sb Lead Free Solder Alloy
    A.A.El-Daly, Y.Swilem, A.E.Hammad
    J. Mater. Sci. Technol., 2008, 24 (06): 921-925. 
    Abstract   HTML   PDF (715KB)
    It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrease the onset melting temperature (233℃) of this alloy to 203.5℃ and 216℃, respectively. The results indicate that the Sn-5Sb-1.5Au alloy has very good ultimate tensile strength (UTS), ductility, and fusion heat, which are better than both those of the Sn-5Sb-3.5Ag and Sn-5Sb alloys. The formation of intermetallic compounds (IMCs) AuSn4 and Ag3Sn enhanced the microstructure stability, while retained the formation of SbSn precipitates in the solidification microstructure, thus significantly improved the strength and ductility. For all alloys, both UTS and yield stress (σy) increase with increasing strain rate and decrease with increasing temperature in tensile tests, but changes of ductility are generally small with inconsistent trends.
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    Electropolishing of NiTi for Improving Biocompatibility
    Wei WU, Xinjie LIU, Huimin HAN, Dazhi YANG, Shoudong LU
    J. Mater. Sci. Technol., 2008, 24 (06): 926-930. 
    Abstract   HTML   PDF (850KB)
    A modified electrolyte (CH3COOH-HClO4-A-B) for electropolishing (EP) of NiTi was presented for improving the corrosion resistance and biocompatibility of the alloy. Using the proposed parameters, a homogeneous and uniform surface was obtained. Atomic force microscopy (AFM) revealed that the surface roughness (Ra) for EP sample (23.21 nm) was close to mechanical polishing (MP) sample (19.36 nm). Analysis by X-ray photoelectron spectroscopy (XPS) showed that Ti/Ni ratio increased from 3.1 for MP sample to 27.6 for EP sample. Measurements using potentiodynamic polarization in Hanks0 solution showed that no pitting occurred for EP sample even though the applied potential increased up to 1500 mV (vs SCE), while the MP sample was broken down at 650 mV. The present study indicates that electropolishing NiTi with this modified electrolyte contributes to the improved biocompatibility of NiTi.
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    A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications
    Montasser DEWIDAR, H.Fouad MOHAMED, Jae-Kyoo LIM
    J. Mater. Sci. Technol., 2008, 24 (06): 931-935. 
    Abstract   HTML   PDF (1925KB)
    Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using space-holder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters (0.56, 0.8, and 1 mm) were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.
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    Interfacial Interaction in Coated Carbon Fibre Reinforced Aluminous Mg-based Composites
    Kun LI, Nanlin SHI, Jun GONG, Chao SUN
    J. Mater. Sci. Technol., 2008, 24 (06): 936-940. 
    Abstract   HTML   PDF (1791KB)
    Four kinds of Mg alloys reinforced with carbon fibres were fabricated by a gas pressure infiltration technique. The fibres were pre-coated a SiO2 layer prior to fabrication. Different microstructures and interactions in the fibre-matrix interface of these composites were observed by transmission electron microscopy (TEM). The results showed that the interfacial interaction strongly depended on the content of Al in the Mg-based matrices. The microstructure of the interface could then be controlled by adjusting the Al content of the Mg-based matrix. In addition, fibres extracted from different Mg-based matrix all had some degradation owing to the interfacial reaction and the fibre-matrix interdiffusion.
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    SiC-Si-ZrSiO4 Multiphase Oxidation Protective Coating for Carbon/Carbon Composites
    Yulei ZHANG, Hejun LI, Qiangang FU, Kezhi LI, Dangshe HOU
    J. Mater. Sci. Technol., 2008, 24 (06): 941-944. 
    Abstract   HTML   PDF (1361KB)
    In order to improve the anti-oxidation property of carbon/carbon (C/C) composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon composites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD (X-ray diffraction), SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy). Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock resistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.
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    Prediction on Carbon/Carbon Composites Ablative Performance by Artificial Neutral Net
    Guanghui BAI, Songhe MENG, Boming ZHANG, Yang LIU
    J. Mater. Sci. Technol., 2008, 24 (06): 945-952. 
    Abstract   HTML   PDF (1302KB)
    A preliminary estimation of ablation property for carbon-carbon composites by artificial neutral net (ANN) method was presented. It was found that the carbon-carbon composites' density, degree of graphitization and the sort of matrix are the key controlling factors for its ablative performance. Then, a brief fuzzy mathematical relationship was established between these factors and ablative performance. Through experiments, the performance of the ANN was evaluated, which was used in the ablative performance prediction of C/C composites. When the training set, the structure and the training parameter of the net change, the best match ratio of these parameters was achieved. Based on the match ratio, this paper forecasts and evaluates the carbon-carbon ablation performance. Through experiences, the ablative performance prediction of carbon-carbon using ANN can achieve the line ablation rate, which satisfies the need of precision of practical engineering fields.
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    Influence of Fabric Parameters on Microstructure, Mechanical Properties and Failure Mechanisms in Carbon-Fibre Reinforced Composites
    B.Wielage, D.Richter, H.Mucha, Th.Lampke
    J. Mater. Sci. Technol., 2008, 24 (06): 953-959. 
    Abstract   HTML   PDF (2163KB)
    The effects of fibre/matrix bonding, fabric density, fibre volume fraction and bundle size on microstructure, mechanical properties and failure mechanisms in carbon fibre reinforced composites (plastic and carbon matrix) have been investigated. The microstructure of unloaded and cracked samples was studied by optical microscopy and scanning electron microscopy (SEM), respectively whereas the mechanical behaviour was examined by 3-point bending experiments. Exclusively one type of experimental resole type phenolic resin was applied. A strong fibre/matrix bonding, which is needed for high strength of carbon fibre reinforced plastic (CFRP) materials leads to severe composite damages during the pyrolysis resulting in low strength, brittle failure and a very low utilisation of the fibres strain to failure in C/C composites. Inherent fabric parameters such as an increasing fabric density or bundle size or a reduced fibre volume fraction introduce inhomogenities to the CFRP0s microstructure. Results are lower strength and stiffness whereas the strain to failure increases or remains unchanged. Toughness is almost not affected. In C/C composites inhomogenities due to a reduced bundle size reduce strain to failure, strength, stiffness and toughness. Vice versa a declining fibre volume fraction leads to exactly the opposite behaviour. Increasing the fabric density (weight per unit area) causes similar effects as in CFRPs.
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    Critical Property of the Geometric Phase in the Dicke Model with the Dipole-dipole Interactions
    Yunfeng WU, Ping ZHANG, Jianzhou ZHENG
    J. Mater. Sci. Technol., 2008, 24 (06): 960-962. 
    Abstract   HTML   PDF (352KB)
    We obtained the ground-state energy level and associated geometric phase in the Dicke model with the dipole-dipole interactions analytically by the Holstein-Primakoff transformation and the boson expansion approach in the thermodynamic limit. The nonadiabatic geometric phase induced by the photon field was derived with the time-dependent unitary transformation. It is shown that dipole-dipole interactions have a deep influence on scaled behavior of the geometric phase at the critical point.
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CN: 21-1315/TG
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