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ISSN 1005-0302
CN 21-1315/TG
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  Current Issue
      28 May 2011, Volume 27 Issue 5 Previous Issue    Next Issue
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    Thin Film and Coatings
    Effect of Heat Treatment on the Microstructure and Residual Stresses in (Ti,Al)N Films
    Ying Yang, Shengsheng Zhao, Jun Gong, Xin Jiang, Chao Sun
    J. Mater. Sci. Technol., 2011, 27 (5): 385-392. 
    Abstract   HTML   PDF
    (Ti,Al)N films were fabricated by arc ion plating (AIP) and then annealed within a range of temperatures from 200 to 500°C for 30 min in vacuum. The results indicate that the average residual stresses decrease slightly from −5.84 to −4.98 GPa with increasing annealing temperature. The stress depth  distribution evolves from a sharp ``bell" shape to a mild ``bell" shape, suggesting a more uniform stress state in the annealed films. The microstructure of the films was also investigated in detail. The as-deposited film consists of fine columnar crystals with an amorphous phase at the interface. During heat treatment, the columnar subgrain growth was observed; meanwhile, the phenomenon of crystallization has been identified at the interface. Further more, the relationship between the residual stresses and the microstructure of the films was explored and highlighted. In addition, there is no hardness degradation of the films during heat treatment.
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    Effect of Enhanced Plasma Density on the Properties of Aluminium Doped Zinc Oxide Thin Films Produced by DC Magnetron Sputtering
    Jun Gong, Xiaobo Zhang, Zhiliang Pei, Chao Sun, Lishi Wen
    J. Mater. Sci. Technol., 2011, 27 (5): 393-397. 
    Abstract   HTML   PDF
    Aluminum doped zinc oxide (AZO) thin films were prepared by DC magnetron sputtering at low substrate temperature. A coaxial solenoid coil was placed near the magnetron target to enhance the plasma density (Ji). The enhanced plasma density improved significantly the bulk resistivity (ρ) and its homogeneity in spatial distribution of AZO films. X-ray diffraction (XRD) analysis revealed that the increased Ji had influenced the crystallinity, stress relaxation and other material properties. The AZO films deposited in low plasma density (LPD) mode showed marked variation in ρ (ranging from ~6.5×10-2 to 1.9×10-3 ­Ω·cm), whereas those deposited in high plasma density (HPD) mode showed a better homogeneity of films resistivity (ranging from ~1.3×10-3 to 3.3×10-3 ­Ω·cm) at different substrate positions. The average visible transmittance in the wavelength range of 500−800 nm was over 80%, irrespective of the deposition conditions. The atomic force microscopy (AFM) surface morphology showed that AZO films deposited in HPD mode were smoother than that in LPD mode. The high plasma density produced by the coaxial solenoid coil improved the electrical property, surface morphology and the homogeneity in spatial distribution of AZO films deposited at low substrate temperature.
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    Effect of Phosphor Addition on Intergranular Exchange Coupling of Co-Pt Thin Films
    Bo Yang, Gaowu Qin, Wenli Pei, Song Li, Yuping Ren, Shunji Ishio
    J. Mater. Sci. Technol., 2011, 27 (5): 398-402. 
    Abstract   HTML   PDF
    In this paper, ternary Co-Pt-P thin films were prepared by magnetron sputtering with platinum and home-made Co-P chips pasted on the cobalt target. The structure and magnetic properties were investigated by X-ray difraction (XRD) and vibrating sample magnetometer (VSM), respectively. With increasing phosphor content, the coercivities of Co-12 at.% Pt-P films increase from 1034 to 1525 Oe owing to the exchange decoupling among magnetic grains. The decrease of inter-granular exchange coupling was confirmed by delta-M curve measurement and magnetic force microscopy (MFM). Transmission electronic microscopy (TEM) with nano-beam composition analysis shows that phosphor segregated at cobalt-based grain boundaries is responsible for
    the exchange decoupling. It is thus suggested that the phosphor addition is effective to tune the exchange coupling of magnetic grains, particularly for perpendicular recording media.
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    Structure, Optical Property and Thermal Stability of Copper Nitride Films Prepared by Reactive Radio Frequency Magnetron Sputtering
    Jianrong Xiao, Yanwei Li, Aihua Jiang
    J. Mater. Sci. Technol., 2011, 27 (5): 403-407. 
    Abstract   HTML   PDF
    Copper nitride (Cu3N) films were prepared by reactive radio frequency magnetron sputtering at various nitrogen partial pressures, and the films were annealed at different temperatures. The crystal structure of the films was identified by X-ray diffraction technique. The Cu3N films have a cubic anti-ReO3 structure, and lattice constant is 0.3855 nm. With increasing nitrogen partial pressure, the Cu3N films are strongly textured with the crystal direction [100]. The atomic force microscope images show that the films presence a smooth and compact morphology with nanocrystallites of about 70 nm in size. The films were further characterized by UV-visible spectrometer, and the optical band gap of the films was calculated from the Tauc equation. The typical value of optical band gap of the films is about 1.75 eV, and it increases with increasing nitrogen partial pressure. The thermal property of the films was measured by thermogravimetry, and the decomposition temperature of the films was about 530 K.
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    Influence of Re on the Properties of a NiCoCrAlY Coating Alloy
    J.J. Liang, H. Wei, Y.L. Zhu, X.F. Sun, Z.Q. Hu, M.S. Dargusch, X.D. Yao
    J. Mater. Sci. Technol., 2011, 27 (5): 408-414. 
    Abstract   HTML   PDF
    MCrAlY can serve as stand-alone overlay coatings or bond coats in thermal barrier coating systems, and its properties play a vital role in determining the performance of these coating systems. In order to further understand the behavior of MCrAlY coatings, several NiCoCrAlY model alloys with different levels of Re (0.3 wt%, 6 wt%, and 9 wt%) were investigated. Microstructural observation showed the addition of Re promoted the precipitation of Cr-rich phases, such as α-Cr and σ. The presence of α-Cr lowered the coefficient of thermal expansion (CTE) of the coating alloys, which could reduce the CTE mismatch at the scale-metal interface. The solid solution strengthening effect of Re is responsible for an increase in Rockwell hardness of the coating alloys. But the isothermal oxidation resistance at 1100°C was deteriorated due to the precipitation of brittle α-Cr phase, a phase of inferior oxidation resistance compared with β-NiAl and γ-Ni.
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    Novel Precessing and Characterization Methods
    A Novel Method to Improve the Electrochemical Performance of LiMn2O4 Cathode Active Material by CaCO3 Surface Coating
    Halil Sahan, Huseyin Goktepe and Saban Patat
    J. Mater. Sci. Technol., 2011, 27 (5): 415-420. 
    Abstract   HTML   PDF
    Spinel LiMn2O4 was synthesized by glycine-nitrate method and coated with CaCO3 in order to enhance the electrochemical performance at room temperature (25°C) and 55°C. The uncoated and CaCO3-coated LiMn2O4 materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. XRD and SEM results indicated that CaCO3 particles encapsulated the surface of the LiMn2O4 without causing any structural change. The charge-discharge tests showed that the specific discharge capacity fade of pristine electrode at 25 and 55°C were 25.5% and 52%, respectively. However, surface modified cathode shows 7.4% and 29.5% loss compared to initial specific discharge capacity at 70th cycle for 25 and 55°C, respectively. The improvement of electrochemical performance is attributed to suppression of Mn2+ dissolution into electrolyte via CaCO3 layer.
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    A Method to Adjust Dielectric Property of SiC Powder in the GHz Range
    Xiaolei Su, Jie Xu, Zhimin Li, Junbo Wang, Xinhai He, Chong Fu, Wancheng Wang
    J. Mater. Sci. Technol., 2011, 27 (5): 421-425. 
    Abstract   HTML   PDF
    The SiC powders by Al or N doping have been synthesized by combustion synthesis, using Al powder and NH4Cl powder as the dopants and polytetrafluoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the Al and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2−12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure Al or N doping and decrease by the Al and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.
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    Fabrication, Sintering and Electrical Properties of (Ca0.61,Nd0.26)TiO3 Nanoparticles Doped with Li-Cu-B
    Fei Wu, Qilong Zhang, Hui Yang
    J. Mater. Sci. Technol., 2011, 27 (5): 426-430. 
    Abstract   HTML   PDF
    A sol-gel processing was used to synthesize (Ca0.61,Nd0.26)TiO3 (CNT) nanoparticles doped with Li-Cu-B at low temperature. Orthorhombic perovskite structure phase with a small amount of Li3BO3 secondary phase was formed by calcining the xerogels at 300°C, and monodisperse CNT nano-powders with the grain size of 10−15 nm could be obtained. By using these nanocrystalline CNT powders, dense CNT ceramics could be achieved at the low sintering temperature of 1100°C due to the effect of the small size nanoparticles and liquid phase Li3BO3. And the dielectric properties with dielectric constant (εr= 89.52), quality value factors with frequency (Q£f=17148 GHz) and the temperature coefficient of resonant frequency (τf ) value of +239×10-6/°C were achieved.
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    Preparation and Characterization of Porous Calcium Phosphate Bioceramics
    Honglian Dai, Xinyu Wang, Yinchao Han, Xin Jiang, Shipu Li
    J. Mater. Sci. Technol., 2011, 27 (5): 431-436. 
    Abstract   HTML   PDF
    β-tricalcium phosphate (β-TCP) powder and Na2O-CaO-MgO-P2O5 glass binder were synthesized and mixed, and then the biodegradable porous calcium phosphate ceramics were successfully prepared by foaming and sintering at 850°C. The as-prepared ceramics possess a high porosity with partial three-dimension interconnected macro- and micro-pores. As in vitro experiment testified, the calcium phosphate ceramics (CPCs) has good degradability.
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    Mechanical and Functional Properities of Materials
    Microstructure and Elevated Temperature Tensile Behavior of Directionally Solidified Ni-rich NiAl-Mo(Hf) Alloy
    Ping Han, Yihui Qi, Jianting Guo
    J. Mater. Sci. Technol., 2011, 27 (5): 437-442. 
    Abstract   HTML   PDF
    The microstructure, high strain rate superplasticity and tensile creep behavior of directionally solidified (DS) NiAl-Mo(Hf) alloy have been investigated. The alloy exhibits dendritic structure, where dendritic arm is NiAl phase, interdendritic region is Ni3Al phase, and Mo-rich phase distributes in the NiAl and Ni3Al phases. The alloy exhibits high strain rate superplastic deformation behavior, and the maximum elongation is 104.2% at 1373 K and strain rate  of  1.04×10-2 s-1. The balance between strain hardening (by dislocation glide) and strain softening (by dynamic recovery and recrystallization) is responsible for the superplastic deformation. All the creep curves of the DS NiAl-Mo(Hf) alloy have similar shape of a short primary creep and dominant steady creep stages, and the creep strain is great. The possible creep deformation mechanism was also discussed. The creep fracture data follow the Monkman-Grant relationship.
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    Effect of Layers Position on Fracture Toughness of Functionally Graded Steels in Crack Divider Configuration
    Ali Nazari, Jamshid Aghazadeh Mohandesi, Shadi Riahi
    J. Mater. Sci. Technol., 2011, 27 (5): 443-452. 
    Abstract   HTML   PDF
    In the present study, fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steels slices with various thicknesses and arrangements as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels in crack divider configuration has been found to depend on the composites' type together with the volume fraction and the position of the containing phases. According to the area under stress-strain curve of each layer in the functionally graded steels, a mathematical model has been presented for predicting fracture toughness of composites by using the rule of mixtures. The fracture toughness of each
    layer has been modified according to the position of that layer where for the edge layers, net plane stress condition was supposed and for the central layers, net plane strain condition was presumed. There is a good agreement between experimental results and those acquired from the analytical model.
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    Uniaxial Ratcheting Behaviors of Metals with Diffent Crystal Structures or Values of Fault Energy: Macroscopic Experiments
    Guozheng Kang, Yujie Liu, Yawei Dong,Qing Gao
    J. Mater. Sci. Technol., 2011, 27 (5): 453-459. 
    Abstract   HTML   PDF
    The uniaxial ratcheting behaviors of several metals with different crystal structures or values of fault energy were observed by the stress-controlled cyclic tests at room temperature. The prescribed metals included 316L stainless steel, pure copper, pure aluminum, and ordinary 20# carbon steel. The effects of applied mean stress, stress amplitude and stress ratio on the uniaxial ratcheting were also investigated. The observations show that different crystal structures or values of fault energy result in more or less different ratcheting behaviors for the prescribed metals. The different ratcheting behaviors are partially caused by the variation of dislocation mobility.
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    Influence of Lithium Oxide Addition on the Sintering Behavior and Electrical Conductivity of Gadolinia Doped Ceria
    Minfang Han, Ze Liu, Su Zhou, Lian Yu
    J. Mater. Sci. Technol., 2011, 27 (5): 460-464. 
    Abstract   HTML   PDF
    Ceria-based electrolytes have been widely researched in intermediate-temperature solid oxide fuel cell (SOFC), which might be operated at 500−600°C. Sintering behavior with lithium oxide as sintering additive and electrical conductivity of gadolinia doped ceria (Gd0.1Ce0.9O2-δ, GDC10) electrolyte was studied in this paper by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). As the results, the fully dense GDC10 electrolytes are obtained at a low temperature of 800°C with 2.5 mol% Li2O as sintering additive (called 5LiGDC800). During sintering process, lithium oxides adsorbed by around GDC10 surface help to sinter at 800°C and are kept at the grain boundary of GDC10 in the end. The fine
    grains of 100−400 nm and high electrical conductivity of 0.014 S/cm at 600°C in 5LiGDC800 were achieved, which contributed to the lower sintering temperature and enhanced grain boundary conductivity, respectively. Lithium, staying at grain boundary, reduces the depletion of oxygen vacancies in the space charge layers and increases the oxygen vacancy concentration in the grain boundary, which leads to improve the total electrical conductivity of 5LiGDC800.
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    Far Infrared Optical Properties of Bulk Wurtzite Zinc Oxide Semiconductor
    Pohkok Ooi, Saicheong Lee, Shashiong Ng, Zainuriah Hassan, Haslan Abu Hassan
    J. Mater. Sci. Technol., 2011, 27 (5): 465-470. 
    Abstract   HTML   PDF
    Polarized far infrared (FIR) reflectance technique was applied to study the optical properties of a bulk wurtzite zinc oxide (ZnO) single crystal. Room temperature polarized FIR reflectance spectra were taken at various angles of incidence, from 20° to 70°. The theoretical polarized FIR reflectance spectra were simulated based on the anisotropic dielectric function model. Good agreement was achieved between the experimental and the theoretical FIR reflectance spectra. Through this work, a complete set of reststrahlen parameters of a bulk wurtzite ZnO at the Brillouin zone centre was obtained. Additionally, other FIR optical properties such as the real and the imaginary parts of the complex dielectric function, real and imaginary parts of the refractive index, the absorption coefficient and the reciprocal of the absorption coefficient were also obtained by using numerical calculation.
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    Modeling and Simulations
    Internal Stress Distribution Model of the Magnetomechanical Hysteresis of Fe-Cr-Al Based Alloys
    Renrong Lin, Wei Jin, Mingzhou Cao, Rui Yang
    J. Mater. Sci. Technol., 2011, 27 (5): 471-474. 
    Abstract   HTML   PDF
    The damping capacities of Fe-13Cr-6Al, Fe-12Cr-1Mo-6Al and Fe-12Cr-1Mn-6Al (at.%) alloys as a function of strain-amplitude tested in a given static load are characterized in the 3-point bending deformation mode. After being modified, Smith-Birchak model is applied to describe the results. It is shown that the modified model agrees with the experimental data much better than the original one. Finally, the influences of stress factors on the damping capacity of the alloys are analyzed.
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    Orientation Relationships between Ferrite and Cementite by Edge-to-edge Matching Principle
    Ning Zhong, Xiaodong Wang, Zhenghong Guo, Yonghua Rong
    J. Mater. Sci. Technol., 2011, 27 (5): 475-480. 
    Abstract   HTML   PDF
    The crystallographic features of pearlite were investigated by experiments and edge-to-edge matching principle. Two new orientation relationships between ferrite and cementite were determinated by selected area electron diffraction and then explained by our modified edge-to-edge matching method. The  consistence of the experimental results with theoretical prediction confirms the practicability of the modified edge-to-edge matching model.
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ISSN: 1005-0302
CN: 21-1315/TG
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