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ISSN 1005-0302
CN 21-1315/TG
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      28 November 2006, Volume 22 Issue 06 Previous Issue    Next Issue
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    Research Articles
    One-dimensional (1D) ZnS Nanomaterials and Nanostructures
    Xiaosheng FANG, Lide ZHANG
    J. Mater. Sci. Technol., 2006, 22 (06): 721-736. 
    Abstract   HTML   PDF (3313KB)

    One-dimensional (1D) nanomaterials and nanostructures have received much attention due to their potential interest for understanding fundamental physical concepts and for applications in constructing nanoscale electric and optoelectronic devices. Zinc sulfide (ZnS) is an important semiconductor compound of II-VI group, and the synthesis of 1D ZnS nanomaterials and nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. This paper reviews the recent progress on 1D ZnS nanomaterials and nanostructures, including nanowires, nanowire arrays, nanorods, nanobelts or nanoribbons, nanocables, and hierarchical nanostructures etc. This article begins with a survey of various methods that have been developed for generating 1D nanomaterials and nanostructures, and then mainly focuses on structures, synthesis, characterization, formation mechanisms and optical property tuning, and luminescence mechanisms of 1D ZnS nanomaterials and nanostructures. Finally, this review concludes with personal views towards future research on 1D ZnS nanomaterials and nanostructures.

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    Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys
    Yongbo XU, Yilong BAI, M.A.Meyers
    J. Mater. Sci. Technol., 2006, 22 (06): 737-746. 
    Abstract   HTML   PDF (769KB)
    α-titanium and its alloys with a dual-phase structure (α+β) were deformed dynamically under strain rate of about 104 s-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate (9×105 s-1) deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products (α2) had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.
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    Effects of External Electric Field on AlN Precipitation and Recrystallization Texture of Deep-drawing 08Al Killed Steel Sheet
    Xiang ZHAO, Zhuochao HU, Liang ZUO
    J. Mater. Sci. Technol., 2006, 22 (06): 747-750. 
    Abstract   HTML   PDF (562KB)
    The effects of an electric field on AlN precipitation and recrystallization texture were investigated. Cold-rolled 08Al killed steel sheets were annealed at 550℃ according to the two-step processes, for various maintaining times, with and without applying an electric field. It was found that the electric field promotes the precipitation of the second phase (AlN particles), strengthens the γ-fiber and weakens the γ-fiber texture component in the recrystallized specimens. A possible explanation for the reinforcement of α-fiber texture by the electric field is that the second phase AlN particle promotes the growth of α-fiber at the expense of differently oriented grains.
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    Interface Migration between Martensite and Austenite during Quenching and Partitioning (Q&P) Process
    Ning ZHONG, Xiaodong WANG, Yonghua RONG, Li WANG
    J. Mater. Sci. Technol., 2006, 22 (06): 751-754. 
    Abstract   HTML   PDF (624KB)
    An Fe-0.2C-1.5Si-1.67Mn steel was subjected to quenching and partitioning (Q&P) process, and the interface migration between martensite and austenite at an elevated partitioning temperature was observed. The interface migration is excluded in constrained paraequilibrium (CPE) model. Based on “endpoint” predicted by CPE model the thermodynamic condition of interface migration is analyzed, that is, the difference in the chemical potential of iron in both ferrite (martenisite) and austenite produces the driving force of the iron atoms to migrate from one phase to the other phase. In addition, the interface migration can change the austenite fraction; as a result, the austenite fraction at partitioning temperature may be higher than that at quenching temperature through the interface migration, but this phenomenon cannot be explained by CPE model.
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    Solidification Structure of Low Carbon Steel Strips with Different Phosphorus Contents Produced by Strip Casting
    Na LI, Zhenyu LIU, Yiqing QIU, Zhaosen LIN, Xianghua LIU, Guodong WANG
    J. Mater. Sci. Technol., 2006, 22 (06): 755-758. 
    Abstract   HTML   PDF (2453KB)

    In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.

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    Microstructures and Mechanical Properties of Nb-Ti Bearing Hot-rolled TRIP Steels
    Yu CHEN, Guoyi TANG, Haoyang TIAN, Feipeng LI, Yu ZHANG, Lihui WANG, Zhaojun DENG, Dexing LUO
    J. Mater. Sci. Technol., 2006, 22 (06): 759-762. 
    Abstract   HTML   PDF (656KB)
    Nb-Ti hot-rolled TRIP-assisted steel with high plasticity and appropriate volume percentage of retained austenite based on fine ferrite grain have been developed in the experiment. The test results showed that niobium tend to exist in solution state in matrix with less precipitation, and niobium-titanium could be precipitated in form of (Nb, Ti)C or (Nb, Ti) (C, N), which play an important role in increasing yield strength (from 495 MPa to 610 MPa). Besides, the retained austenite had a positive effect on improving the plasticity by transformation into martensite during tensile deformation.
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    Influence of Hot Deformation and Subsequent Austempering on the Mechanical Properties of Hot Rolled Multiphase Steel
    Zhuang LI, Di WU
    J. Mater. Sci. Technol., 2006, 22 (06): 763-768. 
    Abstract   HTML   PDF (600KB)
    Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength (σb), total elongation (δ) and the product of ultimate tensile strength and total elongation (σb•δ) reach the maximum values (791 MPa, 36% and 28476 MPa%, respectively) at optimal processes.
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    Effect of Heat Treatment on Prior Grain Size and Mechanical Property of a Maraging Stainless Steel
    Kai LIU, Yiyin SHAN, Zhiyong YANG, Jianxiong LIANG, Lun LU, Ke YANG
    J. Mater. Sci. Technol., 2006, 22 (06): 769-774. 
    Abstract   HTML   PDF (918KB)
    Effect of the heat treatment, including solution treatment (ST) and aging treatment (AT), on the prior austenite grain (PAG) size, microstructure and mechanical properties of a precipitation hardening maraging stainless steel was investigated. The results indicate that the relations between PAG size and yield strength (σy) under both ST and AT conditions obey the Hall-Petch relationship. Furthermore, after ST at 1050℃ for 1 h+cryogenic treated (CT) at -70℃ for 8 h+AT at 535℃ for 4 h, the tested steel showed its ultimate tensile strength (σb) and σy over 1900 MPa and 1750 MPa, respectively.
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    Microstructure and Property of Hypereutectic High Chromium Cast Iron Prepared by Slope Cooling Body-Centrifugal Casting Method
    Zhifu HUANG, Ji, ong XING, Anfeng ZHANG
    J. Mater. Sci. Technol., 2006, 22 (06): 775-778. 
    Abstract   HTML   PDF (900KB)
    In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method (SC-CCM), and its microstructure and impact toughness were investigated, respectively. The results indicated that, first, the primary carbides in the microstructure are prominently finer than those in the hypereutectic high Cr cast iron prepared by conventional casting method. Second, in the ring-type ingot, the primary carbides near radial outer field are finer than those near radial inner field; furthermore, there is dividing field in the microstructure. Finally, the impact toughness values of the specimens impacted on the radial outer face and on the radial inner face are improved respectively about 36% and 138% more than that of the hypereutectic high Cr one prepared by conventional casting method.
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    Characterization of Phases in an as-cast Copper-Manganese-Aluminum Alloy
    J.Iqbal, F.Hasan, F.Ahmad
    J. Mater. Sci. Technol., 2006, 22 (06): 779-784. 
    Abstract   HTML   PDF (1260KB)
    Copper-manganese-aluminum (CMA) alloys, containing small additions of Fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their microstructure can show wide variations. The morphology, crystallography and composition of the phases presented in an as-cast (CMA) alloy of nominal composition Cu-14%Mn-8%Al-3%Fe-2%Ni were investigated using optical, electron optical, and microprobe analytical techniques. The as-cast microstructure consisted of the grains of fcc α and bcc β-phases alongwith intermetallic precipitates of various morphologies. The room temperature microstructure exhibited four different types of precipitates inside the α-grains: the ‘large’ dendritic-shaped particles and the cuboid-shaped precipitates, which were rich in Fe and Mn and had an fcc structure, while the ‘small’ dendritic-shaped particles and the globular precipitates were based on Fe3Al and had DO3 structure. These four different morphologies of intermetallic precipitates exhibited discrete orientationrelationships with the α-matrix. The β-grains only contained very small cuboid shaped precipitates, which could only be resolved through transmission electron microscopy. These precipitates were found to be based on Fe3Al and had the DO3 structure.
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    XPS and PAT Study on NiAl Phase Formed in a Superalloy by Pack Cementation
    Hua WEI, Guichen HOU, Xiaofeng SUN, Qi ZHENG, Hengrong GUAN, Zhuangqi HU
    J. Mater. Sci. Technol., 2006, 22 (06): 785-788. 
    Abstract   HTML   PDF (442KB)
    The NiAl phase prepared by pack cementation (PC) on a nickel base superalloy was investigated by X-ray photoelectron spectroscopy (XPS) and positron annihilation technique (PAT). The focus was on the effect of the solid solution of the alloying element from substrate on the binding energy of Ni (Al) 2p peaks and vacancy concentration of the NiAl phase formed in a superalloy. The results showed that the binding energy of Ni 2p peak of the NiAl phase grown in a superalloy was shifted by up to 0.55 eV at the temperature from 850 to 1050℃ towards higher energies and the binding energy of Al 2p peak by up to 1.09 eV in comparison with the NiAl phase formed in pure Ni. The positron lifetimes obtained from the NiAl phase formed in a superalloy were found to be markedly lower than the theoretical values, indicating the decrease in vacancy concentration. The variation of binding energies and vacancy concentration are possibly due to the solid solution of the alloying atoms from the substrate into the NiAl lattice.
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    Tensile properties of Cu with deformation twins induced by SMAT
    Jinyu GUO, Ke WANG, Lei LU
    J. Mater. Sci. Technol., 2006, 22 (06): 789-792. 
    Abstract   HTML   PDF (470KB)
    High density nano-scale deformation twins were introduced in the surface layer of Cu sample by means of surface mechanical attrition treatment (SMAT) at room temperature. The Cu sample with deformation twins shows a yield strength of about 470 MPa in tension tests. The significant strengthening may be attributed to the effective inhibition of slip dislocations by abundant twin boundaries.
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    Influence of Annealing on the Grain Growth and Thermal Diffusivity of Nanostructured YSZ Thermal Barrier Coating
    Na WANG, Chungen ZHOU, Shengkai GONG, Huibin XU
    J. Mater. Sci. Technol., 2006, 22 (06): 793-797. 
    Abstract   HTML   PDF (750KB)
    The nanostructured zirconia coatings were deposited by atmospherically plasma spraying. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction were used to investigate the microstructure of the zirconia coatings. Thermal diffusivity values at normal temperatures have been evaluated by laser flash technique. Effect of annealing on the microstructure evolution of the zirconia coating has been performed. The grains and thermal diffusivity are increased with increasing annealing time and temperature. The grain growth is according to the GRIGC (the grain rotation induced grain coalescence) mechanism. The increase in thermal diffusivity is attributed to the grain growth and the decrease in porosity of nanostructured zirconia coatings.
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    Preparation and Characterization of Silica Aerogels Derived from Ambient Pressure
    Jun SHEN, Zhihua ZHANG, Guangming WU, Bin ZHOU, Xingyuan NI, Jue WANG
    J. Mater. Sci. Technol., 2006, 22 (06): 798-802. 
    Abstract   HTML   PDF (4413KB)
    Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by silylation and drying under ambient pressure. The specific surface area, pore size distribution and thermal conductivity of the silica aerogels were investigated and the results showed that the diameter of the silica particles is about 6 nm and the average pore size of the silica aerogels is 14.7 nm. The specific surface area of which is about 1000 m2•g-1 and the thermal conductivity is about 0.014 wm-1•K-1 at room temperature and pressure of 1.01×105 Pa. The Si-CH3 groups were also detected on the internal surface of the silica aerogels, which show hydrophobic. Silica aerogels derived by this technique is low cost and have wide applications.
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    Nanosized Ni-Mn Oxides Prepared by the Citrate Gel Process and Performances for Electrochemical Capacitors
    Jianxin ZHOU, Xiangqian SHEN, Maoxiang JING
    J. Mater. Sci. Technol., 2006, 22 (06): 803-806. 
    Abstract   HTML   PDF (739KB)
    Nanosized Ni-Mn oxide powders have been successfully prepared by thermal decomposition of the Ni-Mn citrate gel precursors. The powder materials derived from calcination of the gel precursors with various molar ratios of nickel and manganese at different temperatures and time were characterized using thermal analysis (TG-DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET). The optimized processing conditions of calcination at 400℃ for 1 h with Ni/Mn molar ratio 6 were proved to produce the nanosized Ni-Mn oxide powders with a high specific surface area of 109.62 m2/g and nanometer particle sizes of 15~30 nm. The capacitance characteristics of the nanosized Ni-Mn oxide electrode in various concentrations of KOH solutions were studied by the cyclic voltammetry (CV) and exhibited both a doublelayer capacitance and a Faradaic capacitance which could be attributed to the electrode consisting of Ni-Mn oxides and residual carbons from the organic gel thermal decomposition. A specific capacitance of 194.8 F/g was obtained for the electrode at the sweep rate of 10 mV/s in 4 mol/L KOH electrolyte and the capacitor showed quite high cyclic stability and is promising for advanced electrochemical capacitors.
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    Electrical Properties of Sputter-deposited ZrO2-based Pt/ZrO2/Si Capacitors
    Keunbin YIM, Yeonkyu PARK, Anna PARK, Namhee CHO, Chongmu LEE
    J. Mater. Sci. Technol., 2006, 22 (06): 807-810. 
    Abstract   HTML   PDF (1422KB)
    Pt/ZrO2/Si sandwich structures where ZrO2 is deposited by radio frequency (r.f.) magnetron sputtering using a Zr target in an atmosphere of O2/Ar gas mixture, were fabricated and the effects of the O2/Ar flow ratio in the reactive sputtering process, the annealing temperature, the ZrO2 film thickness on the structure, the surface roughness of ZrO2 films and the electric properties of Pt/ZrO2/Si metal-oxide-semiconductor (MOS) capacitors were investigated. The optimum process parameters of the Pt/ZrO2/Si capacitor based on reactively sputtered-ZrO2 determined in such a way as the capacitance is maximized and the leakage current, the oxide charge, and the interface trap density are minimized that is the O2/Ar flow ratio of 1.5, the annealing temperature of 800℃, and the film thickness of 10 nm. Also the conduction mechanism in the Pt/ZrO2/Si capacitor has been discussed.
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    Polymer Sensitized Quasi Solid-State Photovoltaic Cells Using Derivatives of Polythiophene
    G.K.R.Senadeera, J.M.R.C.Fern, o
    J. Mater. Sci. Technol., 2006, 22 (06): 811-816. 
    Abstract   HTML   PDF (1685KB)
    Substituted thiophene sensitized, nanocrystalline TiO2-based quasi solid-state solar cells were fabricated by using either poly (3-thiophene acetic acid) (P3TAA) or a copolymer with poly (3-thiophene acetic acid)-poly (hexyl thiophene) (P3TAA-PHT) polymers and copper iodide (CuI) as a hole conducting material together with an ionic liquid 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) amide and lithium bis (trifluoromethanesulfone) imide as additives for charge transport promotion. Dramatic enhancements in the cell performances were observed with the additives in CuI. While the cell sensitized with P3TAA generated a short-circuit photocurrent of ~1.45 mA•cm-2, an open-circuit photovoltage of ~345 mV with a total power conversion efficiency of ~0.3% under simulated full sunlight of 100 mW•cm-2 (air mass: 1.5), the cell sensitized with copolymer P3TAA-PHT delivered ~0.25% efficiency under the same conditions with ~1.23 mA•cm-2 as photocurrent and ~371 mV as photovoltage.
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    Diffusion Bonding of Ti-6Al-4V to QAl 10-3-1.5 with Ni/Cu Interlayers
    Wei GUO, Xihua ZHAO, Minxia SONG, Jicai FENG, Biao YANG
    J. Mater. Sci. Technol., 2006, 22 (06): 817-820. 
    Abstract   HTML   PDF (542KB)
    Ti-6Al-4V and QAl 10-3-1.5 diffusion bonding has been carried out with Ni/Cu interlayers. The diffusionbonded joints are evaluated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and microhardness test. Intermetallic compounds at the interface zone are detected by X-ray diffraction (XRD). Interfacial microstructure of TiNi+CuTi3+®-Ti forms at the Ni/Ti-6Al-4V transition zone and Cu (ss. Ni) solid solution forms between Ni/Cu interlayers. The thickness of reaction layer (TiNi) increases with bonding time by a parabolic law: y2=K0exp(-150000/RT)/t, and K0=2.9×10-7 m2/s is figured out from the experiment data.
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    Optimizing the Pulsed Current Gas Tungsten Arc WeldingParameters
    M.Balasubramanian, V.Jayabalan, V.Balasubramanian
    J. Mater. Sci. Technol., 2006, 22 (06): 821-825. 
    Abstract   HTML   PDF (2796KB)
    The selection of process parameter in the gas tungsten arc (GTA) welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy (Ti-6Al-4V) is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density (4.5 g/cm3), excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point (1678℃). The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass (GTA) welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance (ANOVA) and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve's algorithm. Experimental results were provided to illustrate the proposed approach.
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    Kinetic Parameters Estimation of MgO-C Refractory by Shrinking Core Model
    B.Hashemi, Z.A.Nemati, S.K.Sadrnezhaad, Z.A.Moghimi
    J. Mater. Sci. Technol., 2006, 22 (06): 826-832. 
    Abstract   HTML   PDF (3319KB)
    Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5~17 wt pct graphite were isothermally oxidized at 1000~1350℃. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range of 0.08 to 0.55 cm2/s. These values can be utilized to determine the corresponding tortuosity factors of 6.85 to 2.22. Activation energies related to the pore diffusion mechanism appeared to be around (46.4±2) kJ/mol. The estimated intermolecular diffusion coefficients were shown to be independent of the graphite content, when the percentage of the graphite exceeded a marginal value of 10.
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    Ab initio Calculations of Magnetic Properties of Fe16N2
    Dan LI, Yousong GU, Zuoren NIE, Bo WANG, Hui YAN
    J. Mater. Sci. Technol., 2006, 22 (06): 833-838. 
    Abstract   HTML   PDF (891KB)
    Pseudo-potential and plane wave basis-set under the framework of density functional theory have been employed to study the electronic and magnetic properties of Fe16N2, and to have an insight look on the subject of giant magnetic moments reported in Fe16N2. After geometrical optimization, band structures and densities of states have been evaluated together with the atom resolved band populations and magnetic moments. In this paper, we report a theoretical effort to look into the various aspects of the magnetic properties of Fe16N2, including volume effect and distortion effect.
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    Estimation on Magnetic Refrigeration Material (Gd1-xREx)5Si4 (RE=Dy, Ho)
    Wei WU, Zai FENG, Lijun GUO
    J. Mater. Sci. Technol., 2006, 22 (06): 839-842. 
    Abstract   HTML   PDF (387KB)
    A systematic (Gd1-xREx)5Si4 (RE=Dy, Ho) alloys are investigated to estimate their magnetocaloric effect. The Curie points of (Gd1-x REx)Si4 alloys can tunable from 266 K to 336 K when RE=Dy, Ho; x=0~0.35 and 0~0.15, respectively, and decrease nearly linearly with increasing x. These alloys keep orthorhombic structures Ge5Sm4 and exhibit second order transition when they experience in a change magnetic field at about Curie points. The weight and voluminal magnetic entropy changes are about 3.5 J/(kg•K) and 23~29 mJ/(cm3•K) when magnetic field changes 0~2 T. The adiabatic temperatures changes (▽Tad) of these alloys at Curie points are larger than 1 K in a field change 0~1.4 T, the curve of ▽Tad is wide as that of Gd. The relative cooling power is about 0.8~0.9 J/cm3 when field changes 0~2 T, 55% of that of Gd. Comparing with Gd5(Si1-xGex)4, these alloys do not contain expensive element Ge, so that their cost are lower than the former. Because they could work at temperature region 260~340 K due to their Curie points can be tuned, which is an advantage comparing with Gd, these alloys are potential magnetic refrigerants working in a magnetic refrigerator with a low magnetic field at room temperatures.
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    Phase Transformation and Magnetic Properties of Mechanically Alloyed PrCo5-based Magnets
    Xinguo ZHAO, Zhidong ZHANG, Qi YAO, Jinjun LIU, Weijun REN, Wei LIU, Dianyu GENG
    J. Mater. Sci. Technol., 2006, 22 (06): 843-845. 
    Abstract   HTML   PDF (378KB)
    PrCo5-based nanograin PrxCo100-x (x=14~22) alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. The main phase of the alloy for x=14 is Pr2Co17 with rhombohedral Th2Zn17-type. The amount of the Pr2Co17 phase decreases with increasing Pr content, and a nearly single phase PrCo5 with hexagonal CaCu5-type is formed in Pr19Co81 alloy. Further increase in the Pr content leads to the formation of another magnetically hard Pr2Co7 phase with its Curie temperature about 350℃. Remanences decrease monotonously with increasing Pr content, whereas the coercivities increase, reaching a maximum of 2040 kA/m (25.6 kOe) in Pr19Co81 powders milled for 5 h and annealed at 973 K for 2 min, and then decrease for higher Pr content. The high coercivity is attributed to the high anisotropy field of the PrCo5 phase and its nanoscale grain size.
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    Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃
    J. Mater. Sci. Technol., 2006, 22 (06): 846-850. 
    Abstract   HTML   PDF (1368KB)
    CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni+2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 (iron titanate) phase that has a nanocrystallite size of ~80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases (~80 nm) NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni+2=0 shows the lowest reduction extent (20%); as the extent of Ni+2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis (TGA) experiments. The oxidation of the H2-reduced Ni+2 substituted Fe2TiO5 at 500℃ was investigated. As Ni+2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of oxidized samples show also the presence of carbon in the sample containing Ni+2>0, which appears in the form of nanotubes (25 nm).
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    Modeling of Microimprinting of Bulk Metallic Glasses
    Ming CHENG, John A.Wert
    J. Mater. Sci. Technol., 2006, 22 (06): 851-854. 
    Abstract   HTML   PDF (3202KB)
    A finite element analysis (FEA) model has been developed to analyze microimprinting of bulk metallic glasses (BMG) near the glass transition temperature (Tg). The results reveal an approximately universal imprinting response for BMG, independent of surface feature length scale. The scale-independent nature of BMG imprinting derives from the flow characteristics of BMG in the temperature range above Tg. It also shows that the lubrication condition has a mild influence on BMG imprinting in the temperature range above Tg.
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    Three Dimensional FE Analysis on Flange Bending for TC4 Alloy during Shear Spinning
    Xinyu LU, Shihong ZHANG, Hongliang HOU, Jizhen LI, Lixin ZHOU, Zhiqiang LI
    J. Mater. Sci. Technol., 2006, 22 (06): 855-859. 
    Abstract   HTML   PDF (1533KB)
    In this paper, the 3D elastic-plastic simulation was carried out by using finite element (FE) code according to the phenomena of flange keeping straight, bending towards headstock and bending towards tailstock in the shear spinning experiments for TC4 alloy. The simulation results for the three kinds of deformations of the flange agree well with the experimental results. So it is possible to explain the reason of flange bending by analyzing the strain vectors in the flange for the three kinds of deformation, which shows that it is important to apply the FE simulation technology for predicting the defects and optimizing the spinning process of TC4 alloys.
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    Numerical Simulation and Technological Parameter Optimization for Quenching Process of a Gas Turbine Compressor Disk Based on Metallo-Thermo-Mechanics
    Cheng LÜ, Liwen ZHANG, Qing0an TAI, Quying ZHENG, Zhaokun WANG
    J. Mater. Sci. Technol., 2006, 22 (06): 860-864. 
    Abstract   HTML   PDF (817KB)
    Thermal, mechanical and microstructural phenomena are involved in the process of steel quenching. Based on the coupled metallo-thermo-mechanics theory, a calculation model has been developed in this study to simulate the quenching process of a gas turbine compressor disk by finite element method. The thermal physical and mechanical properties were treated as a functions of temperature. Moreover, a series of subroutines were developed on the MARC software platform. Consequently, simulated results on temperature, internal stress and distortion during the quenching were illustrated. With the aid of the simulated results, an optimum quenching scheme was proposed. The quenching process simulated in this study appears to be a promising tool in design of heat-treatment processing parameters for gas turbine compressor disks.
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