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CN 21-1315/TG
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      28 December 2011, Volume 27 Issue 12 Previous Issue    Next Issue
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    Nanomaterials and Nanotechnology
    Hydrogen Storage Alloy and Carbon Nanotubes Mixed Catalyst in a Direct Borohydride Fuel Cell
    Sai Li, Xiaodong Yang, Haiyan Zhu, Yan Liu, Yongning Liu
    J. Mater. Sci. Technol., 2011, 27 (12): 1089-1093. 
    Abstract   HTML   PDF
    In this study, carbon nanotubes (CNTs) were mixed with AB5-type hydrogen storage alloy (HSA), as catalyst for an anode in a direct borohydride fuel cell (DBFC). As comparision, a series of traditional carbon materials, such as acetylene black, Vulcan XC-72R, and super activated carbon (SAC) were also employed. Electrochemical measurements showed that the electrocatalytic activity of HSA was improved greatly by CNTs. The current density of the DBFC employing the HSA/CNTs catalytic anode could reach 1550 mA·cm-2 (at −0.6 V vs the Hg/HgO electrode) and the maximum power density of 65 mW·cm-2 for this cell could be achieved at room temperature. Furthermore, the life time test lasting for 60 h showed that the cell displayed a good stability.
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    Analysis of Dielectric and Electro-optic Responses of Nanomaterials Doped Ferroelectric Liquid Crystal Mixture
    Neeraj, Pankaj Kumar, K.K. Raina
    J. Mater. Sci. Technol., 2011, 27 (12): 1094-1098. 
    Abstract   HTML   PDF
    Dielectric and rotational viscosity measurements of a multi-component ferroelectric liquid crystal mixture were performed by adding a small concentration (0.01 wt%) of silica and multi walled carbon nanotubes (MWCNTs). Liquid crystals turn out to be outstanding hosts for nanomaterials. A remarkable increase in the rotational viscosity was noticed in CNT doped system as compared to silica doped same liquid crystal system. Comparison of dielectric studies shows higher value of permittivity and dielectric losses for silica-doped sample than those of CNT doped sample. The results have been interpreted both experimentally and theoretically.
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    Superplasticity of Ti2448 Alloy with Nanostructured Grains
    M.J. Xiao, Y.X. Tian, G.W. Mao, S.J. Li, Y.L. Hao, R. Yang
    J. Mater. Sci. Technol., 2011, 27 (12): 1099-1104. 
    Abstract   HTML   PDF
    Ti-24Nb-4Zr-8Sn, abbreviated as Ti2448 from its chemical composition in weight percent, is a multifunctional β type titanium alloy with body centered cubic (bcc) crystal structure, and its highly localized plastic deformation behavior contributes significantly to grain refinement during conventional cold processing. In the paper, the nanostructured (NS) alloy with grain size less than 50 nm produced by cold rolling has been used to investigate its superplastic deformation behavior by uniaxial tensile tests at initial strain rates of 1.5×10-2, 1.5×10-3 and 1.6×10-4 s-1 and temperatures of 600, 650 and 700°C. The results show that, in comparison with the coarse-grained alloy with size of 50 ¹m, the NS alloy has better superplasticity with elongation up to ~275% and ultimate strength of 50-100 MPa. Strain rate sensitivity (m) of the NS alloy is 0.21, 0.30 and 0.29 for 600, 650 and 700°C, respectively. These results demonstrate that grain refinement is a valid way to enhance the superplasticity of Ti2448 alloy.
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    Evaluating and Modeling the Mechanical Properties of the Prepared PLGA/nano-BCP Composite Scaffolds for Bone Tissue Engineering
    Mehdi Ebrahimian-Hosseinabadi Fakhredin Ashrafizadeh Mohammadreza Etemadifar Subbu S. Venkatraman
    J. Mater. Sci. Technol., 2011, 27 (12): 1105-1112. 
    Abstract   HTML   PDF
    In this paper, preparation of nano-biphasic calcium phosphate (nBCP), mechanical behavior and load-bearing of poly (lactide-co-glycolide) (PLGA) and PLGA/nBCP are presented. The nBCP with composition of 63/37 (w/w) HA/β-TCP (hydroxyapatite/β-tricalcium phosphate) was produced by heating of bovine bone at 700°C. Composite scaffolds were made by using PLGA matrix and 10-50 wt% nBCP powders as reinforcement  material. All scaffolds were prepared by thermally induced solid-liquid phase separation (TIPS) at -60°C under 4 Pa (0.04 mbar) vacuum. The results of elastic modulus testing were adjusted with Ishai-Cohen and Narkis models for rigid polymeric matrix and compared to each other. PLGA/nBCP scaffolds with 30 wt% nBCP showed the highest value of yield strength among the scaffolds. In addition, it was found that by increasing the nBCP in scaffolds to 50 wt%, the modulus of elasticity was highly enhanced. However, the optimum value of yield strength was obtained at 30 wt% nBCP, and the agglomeration of reinforcing particles at higher percentages caused a reduction in yield strength. It is clear that the elastic modulus of matrix has the significant role in elastic modulus of scaffolds, as also the size of the filler particles in the matrix.
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    Hot Extrusion Process Effect on Mechanical Behavior of Stir Cast Al Based Composites Reinforced with Mechanically Milled B4C Nanoparticles
    A. Alizadeh, E. Taheri-Nassaj, M. Hajizamani
    J. Mater. Sci. Technol., 2011, 27 (12): 1113-1119. 
    Abstract   HTML   PDF
    In this study, aluminum alloy (Al-2 wt% Cu) matrix composites reinforced with 1, 2 and 4 wt% boron carbide nanoparticles fabricated through mechanical milling with average size of 100 nm were fabricated via stir casting method at 850°C. Cast ingots of the matrix alloy and the composites were extruded at 500°C at an extrusion ratio of 10:1 to investigate the effects of hot extrusion on the mechanical properties of the composites. The microstructures of the as-cast and the extruded composites were investigated by scanning electron microscopy (SEM). Density measurement, hardness and tensile tests were carried out to identify the mechanical properties of the composites. The extruded samples revealed a more uniform distribution of B4C nanoparticles. Also, the extruded samples had strength and ductility values superior to those of the as-cast counterparts. In the as-cast and the extruded samples, with increasing amount of B4C nanoparticles, yield strength and tensile strength increased but elongation to fracture decreased.
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    Iron and Steel
    Inhomogeneous Distribution of Second Phase Particles in Grain Oriented Electrical Steels
    Yang Li, Weimin Mao, Ping Yang
    J. Mater. Sci. Technol., 2011, 27 (12): 1120-1124. 
    Abstract   HTML   PDF
    The second phase particles were observed during the whole manufacturing process of conventional grain oriented electrical steels, exhibiting that the areal density of particles in the center was obviously higher than that on the surface at each manufacturing stage. After hot rolling, the approximately equiaxed grains formed upon recrystallization were present on the sheet surface while the deformation structures were retained in the central part. Thus, the dislocation density on the surface was evidently lower than that in the center and this trend became more noticeable after the first cold rolling. Since new precipitates were mainly nucleated at dislocations during both hot rolling and annealing following cold deformation, the difference in dislocation density resulted in the inhomogeneous distribution of particles through the thickness of sheet. According to this, Goss grains, which were usually found near the surface, tended to grow up more easily during the secondary recrystallization treatment.
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    Effects of Mo on the Precipitation Behaviors in High-Nitrogen Austenitic Stainless Steels
    Feng Shi, Yang Qi, Chunming Liu
    J. Mater. Sci. Technol., 2011, 27 (12): 1125-1130. 
    Abstract   HTML   PDF
    Precipitation behaviors of Fe-18Cr-18Mn-0.63N and Fe-18Cr-18Mn-2Mo-0.69N high-nitrogen austenitic stainless steels during isothermally aging at 850°C have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The experimental results show that precipitation displays a discontinuous cellular way and the precipitates are identified as Cr2N in Fe-18Cr-18Mn-0.63N steel. The addition of Mo makes precipitation occur not only at the grain boundary but also inside the grain and precipitation also displays discontinuous cellular way. The precipitates at the grain boundary and in the cell are both identified as Cr2N phase and χ phase and the precipitates inside the grain are identified as Χ phase in Fe-18Cr-18Mn-2Mo-0.69N steel. The nucleations of  Χ phase and Cr2N phase at the grain boundary are both governed by the diffusion of Cr atoms. The formation and growth of χ phase inside the grain are induced by the impoverishment of N atoms with increasing aging time.
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    Dynamic Recrystallization and Precipitation Behavior of Mn-Cu-V Weathering Steel
    Hongyan Wu, Linxiu Du, Xianghua Liu
    J. Mater. Sci. Technol., 2011, 27 (12): 1131-1138. 
    Abstract   HTML   PDF
    The hot deformation behavior of a Mn-Cu-V weathering steel was investigated at temperatures ranging from 850 to 1050°C and strain rates ranging from 0.01 to 5 s-1 using MMS-300 thermal-mechanical simulator. The activation energy for dynamic recrystallization and stress exponent were calculated to be 551 kJ/mol and 7.73, respectively. The accurate values of critical strain were determined by the relationship between work hardening rate and flow stress (θ-σ) curves. The hyperbolic sine constitutive equation was employed to describe the relationship between the peak stress and Zener-Hollomon parameter during hot deformation. The interaction between dynamic recrystallization and dynamic precipitation of V(C,N) at a low strain rate was analyzed. The results showed that precipitation particles size of weathering steel increased with increasing strain at deformation temperature 950°C and strain rate 0.1 s¡1. The calculation results of the recrystallization driving force and pinning force showed that dynamic precipitation could retard the progress of dynamic recrystallization but not prevent it while the pinning forces is less than driving force. On the contrary, dynamic precipitation can effectively prevent the progress of dynamic recrystallization.
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    Analysis of Magnetism in High Nitrogen Austenitic Stainless Steel and Its Elimination by High Temperature Gas Nitriding
    Peng Wan, Yibin Ren, Bingchun Zhang, Ke Yang
    J. Mater. Sci. Technol., 2011, 27 (12): 1139-1142. 
    Abstract   HTML   PDF
    Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent application. This magnetic behavior in high nitrogen stainless steel was investigated by optical microscopy, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and superconducting quantum interference device (SQUID). The results showed that the magnetism came from the composition segregation of ferrite formation elements such as Cr and Mo in the steel and some δ-ferrites were locally formed during the pressurized electroslag remelting process. The magnetism of high nitrogen stainless steel could be eliminated by a proper high temperature gas nitriding (HTGN).
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    Seed Extract of Psidium guajava as Ecofriendly Corrosion Inhibitor for Carbon Steel in Hydrochloric Acid Medium
    K.P.Vinod Kumar, M. Sankara Narayana Pillai, G. Rexin Thusnavis
    J. Mater. Sci. Technol., 2011, 27 (12): 1143-1149. 
    Abstract   HTML   PDF
    The anticorrosion characteristics of the seeds of Psidium guajava (P. guajava) fruits on carbon steel in acid medium were examined with weight loss data and subsequently thermodynamic factors such as heat of adsorption of the inhibitor on the metal surface (Q), change in entropy (?S), change in free energy of the reaction (?G), corrosion rate (CR) and energy of activation for corrosion reaction of carbon steel (E) were also evaluated. Adsorption isotherm was plotted to study the adsorption of the inhibitor on the metal surface with increasing concentration of the inhibitor. The functional groups responsible for inhibition were investigated using Fourier transform infrared (FT-IR) spectra. Electrochemical parameters were evaluated through the potentiodynamic Tafel polarization and impedance spectral studies. Scanning electron microscopy (SEM) micrographs were recorded to investigate the change in surface morphology. The complete study reveals the effciency of seed extract of P. guajava as a safe, ecofriendly and alternate corrosion inhibitor for carbon steel
    in acid medium.
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    Light Weight Metals
    Microstructure Characteristics of the Eutectics of Die Cast AM60B Magnesium Alloy
    Mengwu Wu, Shoumei Xiong
    J. Mater. Sci. Technol., 2011, 27 (12): 1150-1156. 
    Abstract   HTML   PDF
    Under the cold-chamber high pressure die casting (HPDC) process, samples were produced with AM60B magnesium alloy to investigate the microstructure characteristics of the eutectics, especially focusing on the constitution, morphology and distribution of the eutectics over cross section of the castings. Attentions were also paid to study the effect of heat treatment on the eutectics in the die castings. Based on experimental analysis using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), it was determined that fully divorced eutectics consisting of α-Mg and β-Mg17Al12 appeared at the grain boundary of the primary α-Mg in the as-cast microstructure. Islands and networks of β-Mg17Al12 phase were observed in the central region of the castings, while the β-Mg17Al12 phase revealed a more dispersed and granular morphology on the surface layer. The two phases ratio β/α in the central region of the castings was approximately 10%, which was higher than that on the surface layer. Besides, the defect bands contained a higher percentage of the eutectics than the adjacent regions. After aging treatment (T6), only α-Mg phase was detected by XRD in the AM60B magnesium alloy, though a small amount of precipitated β-Mg17Al12 phase was observed at the grain boundary. In contrast to the microstructure of die cast AZ91D magnesium alloy under the same T6 heat treatment, no discontinuous precipitation of the β-Mg17Al12 phase was observed in AM60B magnesium alloy die castings.
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    Effect of Rotation Rate on Microstructures and Mechanical Properties of FSW Mg-Zn-Y-Zr Alloy Joints
    G.M. Xie, Z.Y. Ma, Z.A. Luo, P. Xue, G.D. Wang
    J. Mater. Sci. Technol., 2011, 27 (12): 1157-1164. 
    Abstract   HTML   PDF
    Friction stir welding (FSW) of Mg{Zn{Y{Zr plates with 6 mm in thickness was successfully carried out under a wide range of rotation rates of 600{1200 r/min with a constant traverse speed of 100 mm/min. After FSW, the coarse grains in the parent material (PM) were changed into fine equiaxed recrystallized grains at the nugget zone (NZ). Furthermore, the coarse Mg-Zn-Y particles (W-phase) were broken up and dispersed homogenously into the Mg matrix. With increasing rotation rates, the size of the W-phase particles at the NZ significantly decreased, but the recrystallized grain size tended to increase. The hardness values of the NZs for all the FSW joints were higher than those of the PM, and the lowest hardness values were detected in the heat affected zone (HAZ). The fracture occurred in the thermo-mechanical affected zone (TMAZ) on the advancing side for all the FSW joints in the tensile test, due to the incompatibility of the plastic deformation between the NZ and TMAZ caused by remarkably different orientation of grains and W-phase particles. The strength of FSW joint reaches 90% of that of its PM.
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    Regular Papers
    Preparation of In2O3-Sr2RuErO6 Composite Ceramics by the Spark Plasma Sintering and Their Thermoelectric Performance
    Bo Cheng, Yuanhua Lin, Jinle Lan, Yong Liu, Cewen Nan
    J. Mater. Sci. Technol., 2011, 27 (12): 1165-1168. 
    Abstract   HTML   PDF
    In1.94Zn0.03Ge0.03 O3 and Sr2RuErO6 composite ceramics have been prepared by the spark plasma sintering (SPS) technique. Microstructure studies show that the Sr2RuErO6 phases are randomly dispersed in the In1.94Zn0.03Ge0.03 O3 matrix. The results show that the Seebeck coe±cient increases with increasing the amount of Sr2RuErO6, while the thermal conductivity of the composite samples is lower than that of the In1.94Zn0.03Ge0.03 O3 ceramic. The thermal conductivity of the 7 vol.% Sr2RuErO6 sample can decrease to 2.15 W·m-1·K-1 at 973 K, and the evaluated maximum ZT value is 0.23 for 3 vol.% Sr2RuErO6 samples at 973 K, which makes them promising materials for the thermoelectric devices.
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    Crystallization and Corrosion Resistance of (Fe0.78Si0.09B0.13)100-xNix (x=0, 2 and 5) Glassy Alloys
    Haijian Ma, Weimin Wang, Jie Zhang, Guihua Li, Chongde Cao, Hongdi Zhang
    J. Mater. Sci. Technol., 2011, 27 (12): 1169-1177. 
    Abstract   HTML   PDF
    The crystallization of the (Fe0.78Si0.09B0.13)100-xNix glassy alloys (x=0, 2 and 5) has been investigated by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). Corrosion resistance analyses have been carried out using electrochemical measurements and corrosion products have been analyzed  by scanning electron microscopy (SEM). The experimental results show that the addition of Ni can promote the nucleation of α-Fe, retard the decomposition of the metastable borides, and alter the crystallization mode of the present Fe-based glassy alloys. The lattice constant (aFe 0 ) of α-Fe in the annealed samples shows a decreasing trend with increasing annealing time. The Ni addition can improve the corrosion resistance of the as-quenched Fe-based glassy alloys in H2SO4, NaCl and NaOH solutions. The results indicate that Ni can promote the diffusion of Si atoms during quenching and annealing processes.processes.
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    Broaching Performance of Superalloy GH4169 Based on FEM
    Xiangwei Kong, Bin Li, Zhibo Jin, Wenran Geng
    J. Mater. Sci. Technol., 2011, 27 (12): 1178-1184. 
    Abstract   HTML   PDF
    The nickel-based superalloy GH4169 is an important material for high temperature applications in the aerospace industry. However, due to its poor machinability, GH4169 is hard to be cut and generates saw-tooth chips during high speed machining, which could significantly affect the dynamic cutting force, cutting temperature fluctuation, tool life, and the surface integrity of the parts. In this paper, the saw-tooth chip formation mechanism of superalloy GH4169 was investigated by the elasto-viscoplastic finite element method (FEM). Using the finite element software of ABAQUS/Explicit, the deformation of the part during high speed machining was simulated. The effective plastic strain, the temperature field, the stress distribution, and the cutting force were analyzed to determine the in°uence of the cutting parameters on the saw-tooth chip formation. The study on broaching performance has great effect on selecting suitable machining parameters and improving tool life.
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ISSN: 1005-0302
CN: 21-1315/TG
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