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ISSN 1005-0302
CN 21-1315/TG
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      28 September 2011, Volume 27 Issue 9 Previous Issue    Next Issue
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    Light Weight Metals
    Secondary Solidification Behaviour of AA8006 Alloy Prepared by Suction Casting
    Zhongwei Chen, Haifang Zhang, Yimin Lei
    J. Mater. Sci. Technol., 2011, 27 (9): 769-775. 
    Abstract   HTML   PDF
    Solidification behaviour of AA8006 aluminium alloy in suction casting has been investigated by field emission scanning electron microscopy with energy dispersive spectroscopy (EDS). It is found that there is a secondary solidification process of the remaining liquid in located region of α-Al dendrites, and the cooling rate influences not only the solidification of the primary α-Al dendrite, but also the secondary solidification process of the remaining liquid. With the primary solidification being responsible for the formation of the relatively large α-Al dendrite, a fine and homogeneous microstructure is observed in the secondary solidification. Furthermore, because of the presence of the fine microstructure, the eutectic reaction is confined into small intergranular areas, inducing the formation of the laminar eutectic phase in the primary solidification region and fibrous eutectic phase in the secondary solidification region. EDS analysis shows that the content of Fe is higher in the secondary solidification region, and the enrichment of the solute element further confirms the existence of the secondary solidification.
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    Fatigue Induced Alteration of the Superficial Strength Properties of 2024 Aluminum Alloy
    K.-D. Bouzakis, I. Mirisidis, Sp.G. Pantelakis, A.N. Chamos
    J. Mater. Sci. Technol., 2011, 27 (9): 776-784. 
    Abstract   HTML   PDF
    Aircraft aluminum alloy 2024 T3 specimens have been subjected to constant amplitude fatigue loading at R=0.1. During fatigue, an appreciable increase of the surface hardness of the material at the meso-scale can be observed and captured by means of nanoindentations. Surface hardness increases with increasing fatigue stress amplitude and advancing number of applied fatigue cycles. Observed increase of specimen surface hardening degree during fatigue causes an evolution of superficial mechanical strength properties of the alloy. Stress{strain curves associated with the evoluting superficial mechanical properties are derived, employing a developed finite element method (FEM){supported evaluation procedure of nanoindentation experimental
    results.
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    Optimization of Manganese and Magnesium Contents in As-cast Aluminum-Zinc-Indium Alloy as Sacrificial Anode
    Mohammad R. Saeri, Ahmad Keyvani
    J. Mater. Sci. Technol., 2011, 27 (9): 785-792. 
    Abstract   HTML   PDF
    In this study, effects of manganese and magnesium content on the electrochemical properties of Al-Zn-In sacrificial anode were studied in 0.5 mol/L NaCl solution (pH=5). The aluminum base alloy with different amounts of Mn and Mg were melted at 750°C, then casted at molds at 25°C. Corrosion experiments were mounted to determine the optimal effect of Mn and Mg on the efficiencies of the aluminum alloy anodes. The corroded and unexposed sample surfaces were subjected to microstructure characterization by optical and scanning electron microscopy. Al-Zn-In alloy doped with 0%, 0.01%, 0.05%.0.2% and 0.3% by weights of Mn and 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% by weights of Mg were prepared to determine the effect of Mn and Mg on anode efficiency in the environment. The different microstructures of the evolved Al-Zn-In-Mg-Mn alloy were correlated with the anode efficiencies. The Al-5.0%Zn-2.0%Mg-0.15%Mn-0.02%In gave the best anode efficiency (about 83%). The microstructures of the corroded surface of the optimized alloy revealed decreased distribution of the pockets of localized attacks which are characteristics of pitting (or crevice) corrosion.
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    Microstructure and Hardness of Laser Shocked Ultra-fine-grained Aluminum
    Tiantian He, Yi Xiong, Zhiqiang Guo, Lingfeng Zhang, Fengzhang Ren, Alex A. Volinsky
    J. Mater. Sci. Technol., 2011, 27 (9): 793-796. 
    Abstract   HTML   PDF
    Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then straining at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6μm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3μm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.
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    Effect of Microstructure on Thermal Expansion Coefficient of 7A09 Aluminum Alloy
    Hongzhi Ji, Lin Yuan, Debin Shan
    J. Mater. Sci. Technol., 2011, 27 (9): 797-801. 
    Abstract   HTML   PDF
    The relationship between microstructure evolution and coefficient of thermal expansion (CTE) of 7A09 aluinum alloy was investigated in this paper. Differential scanning calorimetry (DSC) was combined with transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate microstructure evolution taking place in 7A09 aluminum alloy during heating and cooling process. The corresponding CTE curves of the 7A09 alloy were recorded by thermal dilatometer. Results indicated that GPII zones and η' phase were main precipitates in the highest strength tempered (T6) 7A09 alloy. The η phase was the main participate in 7A09 alloy during the cooling process. The nonlinear dependency existed between CTE and temperature in both changing temperature processes. During the heating process, obvious additional contraction of alloy volume was directly caused by phase transition, such as dissolution of ´0 phase, transition from η' to η phase and dissolution of η phase. The additional contraction could slow down the increase of CTE greatly and be expressed in the nonlinearity of CTE curve. Volume and energy changes of alloy system influenced the variation trend of CTE directly, which was caused by the precipitation of ´ phase during the cooling process. These effects were revealed by the corresponding nonlinear change of CTE.
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    Thin Film and Coatings
    AC Conductivity and Dielectric Relaxation Behavior of Sol-gel BaxSr1-xTiO3 Thin Films
    Ala'eddin A. Saif, P. Poopalan
    J. Mater. Sci. Technol., 2011, 27 (9): 802-808. 
    Abstract   HTML   PDF
    BaxSr1-xTiO3 sol-gel thin films with x=0.5, 0.7 and 0.8 have been fabricated as Al/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and 1 MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. Dielectric results show that ε' at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ε'' plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.
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    Influence of Gas Temperature on Microstructure and Properties of Cold Spray 304SS Coating
    Xianming Meng, Junbao Zhang, Jie Zhao, Yongli Liang, Yujun Zhang
    J. Mater. Sci. Technol., 2011, 27 (9): 809-815. 
    Abstract   HTML   PDF
    In the present study, 304 stainless steel coatings were deposited on interstitial-free steel substrates by cold gas dynamic spray technology. The effect of gas temperature on microstructure, micro-hardness, cohesive strength, and electrochemical property of the coatings were investigated and compared. The results showed that increasing gas temperature had a great contribution to enhancing the bonding strength between the deposited particles and making the microstructure more density. Therefore, the porosity of the coatings decreased from 6%±0.5% to 2%±0.3%, and the tensile strength of the coatings increased from 56±4 MPa up to 73±3 MPa. In addition, the corrosion resistance of the coatings was also deeply influenced by process gas temperature. The corrosion kinetics of the coatings were affected by both of the plastic deformation of deposited particles and the porosity in the coatings.
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    Plasma Sprayed NiAl Intermetallic Coating Produced with Mechanically Alloyed Powder
    Mehrshad Moshref Javadi, Hossein Edris, Mahdi Salehi
    J. Mater. Sci. Technol., 2011, 27 (9): 816-820. 
    Abstract   HTML   PDF
    In the present research, mechanically alloyed Ni{Al powder was utilized to develop plasma sprayed coatings, and the effect of the spray distance and heat treatment on the phases, microstructure, and hardness of the coatings were examined. Coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and through microhardness measurements. Although mechanically alloyed Ni-Al powder showed no intermetallic phases, the coatings did. Different spray distances from 5 to 19 cm were employed for plasma spray and the specimens were heat treated at different temperatures, then the amount of oxides, porosity and hardness of the coatings were changed according to the spray condition. The thermal energy of the plasma spray caused the formation of NiAl phases while particles flew to the substrate or after that. Extreme increase in heat treatment temperature and spray distance resulted in oxidation and reduction in the quality of the coating. Furthermore, the best spray distance and heat treatment temperature to gain the NiAl intermetallic coating were established.
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    Optical Properties of Ca0.25Ba0.75Nb2O6 Thin Films Prepared by Spinning Coating
    Yuehua Wang, Min Zhang, Xinyin Zhao, Na Zhao
    J. Mater. Sci. Technol., 2011, 27 (9): 821-825. 
    Abstract   HTML   PDF
    Ca0.25Ba0.75Nb2O6 (CBN25) thin film was prepared on quartz substrate by spinning coating and the optical properties were investigated by a Hitachi U-3410 spectrophotometer and a Metricon 2010 prism coupler. The optical band gap, thickness and refractive index at 632.8 nm of the CBN25 thin film were determined to be 3.65 eV, 529 nm and 2.2258, respectively. The dispersion of the refractive index fitted to Sellmeier relation well and optical waves could be guided into the thin film, which implied that CBN25 thin films were promising for integrated optics and optically active devices.
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    Coercivity Enhancement of Nd{Fe{B Thin Film Magnets through Dy Surface Diffusion Process
    C.Y. You, J. Zhu, N. Tian, Z.X. Lu
    J. Mater. Sci. Technol., 2011, 27 (9): 826-830. 
    Abstract   HTML   PDF
    The Dy capping layer was deposited at different temperatures on the Nd-Fe-B thin films to investigate the mechanism of the coercivity enhancement through the Dy surface diffusion. The highest coercivity of 2005 kA/m (25.2 kOe) was obtained at the Dy deposition temperature of 460°C, which was significantly higher than the value of 1297 kA/m (16.3 kOe) without Dy capping layer. By performing the transmission electron microscopy (TEM) analysis, it was found that some of the grain boundaries were enriched with Nd element, which could be partly ascribed to the promotion by the Dy surface diffusion. In comparison to the evolution of the spin reorientation temperature of Nd2Fe14B phase after the deposition of the Dy capping layer, it is concluded that structural modification plays a significant role in the coercivity enhancement due to the Dy surface diffusion.
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    High Temperature Structural Materials
    Effect of Casting Modulus on Microstructure and Segregation in K441 Superalloy Casting
    Weiguo Jiang, Jiasheng Dong, Li Wang, Langhong Lou
    J. Mater. Sci. Technol., 2011, 27 (9): 831-840. 
    Abstract   HTML   PDF
    Four castings with different modulus have been designed to simulate different thickness sections of a turbine blade during casting process. The microstructure has been observed by optical microscopy (OM) and scanning electron microscopy (SEM). The micro-segregation was tested by energy dispersive spectroscopy (EDS) and the macro-segregation was analyzed by using Metalscan 2500 spectrometers. The experimental results show that the microstructure of casting is affected by modulus apparently. The smaller the modulus, the finer the microstructure. The average grain size of castings with modulus of 0.29, 1.57, 3.16 and 5.0 mm is 0.3, 1.5, 2.7 and 4.3 mm, and the volume fraction of eutectic is 0, 0.1%, 0.2% and 1.0%, respectively. The micro/macro segregation is affected by the modulus apparently. The smaller the modulus, the lower the segregation level. When the modulus of casting increases, the content of Al increases, while the content of W, Cr and Mo decreases both in inner grain and near grain boundary. The content of Al and Mo in inner grain is higher than that near grain boundary, while the content of Cr and W in inner grain is lower than that near grain boundary.
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    High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy
    Y.C. Ma, X.J. Zhao, M. Gao, K. Liu
    J. Mater. Sci. Technol., 2011, 27 (9): 841-845. 
    Abstract   HTML   PDF
    A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-Al alloy in air at 1250°C with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.
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    Regular Papers
    Design of Slant-Form Tool in Precision Reuse of Digital Paper Display
    Pai-Shan Pa
    J. Mater. Sci. Technol., 2011, 27 (9): 846-850. 
    Abstract   HTML   PDF
    A reuse fabrication module using micro electroetching as a precision machining process with a new design of a slant-form tool to remove the defective indium-tin-oxide (ITO) nanostructure from the optical poly-ethyleneterephthalate (PET) surfaces of digital paper display is presented in current studies. The low yield of ITO thin film deposition is an important factor in optoelectronic semiconductor production. The adopted precision reuse process requires only a short period of time to remove the ITO nanostructure easily and cleanly, which is based on technical and economical considerations and is highly efficient. In the current experiment, a large inclined angle of the cathode and a small end radius of the anode take less time for the same amount of ITO removal. A higher feed rate of the optical PET diaphragm combines with enough electric power to drive fast micro electroetching. A small rotational diameter of the anode accompanied by a small width of the cathode corresponds to a higher removal rate for the ITO nanostructure. A pulsed direct current can improve the effect of dreg discharge and is advantageous to couple this current with the fast feed rate of the workpiece. This improvement is associated with an increase in current rating. High rotational speed of the slant-form tool can improve the effect of dregs discharge and is advantageous to associate with the fast feed rate of the workpiece (optical PET diaphragm).
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    Effects of yttrium addition on microstructure, hardness and resistance to wear and corrosive wear of TiNi Alloy
    Hojat Ahmadi, Meisam Nouri
    J. Mater. Sci. Technol., 2011, 27 (9): 851-855. 
    Abstract   HTML   PDF
    TiNi alloy has a high resistance to wear and could be an excellent candidate for various tribological applications. In this paper, it was demonstrated that by addition of yttrium, hardness properties and resistance to wear and corrosive wear of TiNi alloy were improved. New yttrium rich regions were formed in microstructure of TiNi alloy. The improved properties of this alloy by the yttrium addition could be attributed to the formation of these regions. The results showed that there was an optimum content for addition of yttrium between 2% and 5% (in wt%), and above this content the improvement in properties of TiNi became minor.
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    Effect of High Magnetic Field on Growth Behavior of Compound Layers during Reactive Diffusion between Solid Cu and Liquid Al
    B. Xu, W.P. Tong, C.Z. Liu, H. Zhang, L. Zuo, J.C. He
    J. Mater. Sci. Technol., 2011, 27 (9): 856-860. 
    Abstract   HTML   PDF
    The effect of magnetic field on the growth behavior of compound layer was examined at the interface between the solid Cu and liquid Al during reactive diffusion. It was found that the thickness of compound layer was reduced by the high magnetic field. The growth activation energy in β, γ1 and "2 layers under a high magnetic field was larger than those in non magnetic circumstances, the increment percentage being 4.8%, 13.3% and 5.5%, respectively.
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    Synthesis and Electrochemical Properties of Carbon-Mixed LiEr0.02Fe0.98PO4 Cathode Material for Lithium-ion Batteries
    Huseyin Goktepe, Halil Sahan, Ahmet Ulgen, Saban Patat
    J. Mater. Sci. Technol., 2011, 27 (9): 861-864. 
    Abstract   HTML   PDF
    LiEr0.02Fe0.98PO4/C composite cathode was synthesized by a simple solution method with polyethylene glycol (PEG) as the reductive agent and carbon source. The effect of erbium doping on the electrochemical behavior of LiFePO4 was studied in this paper. The samples were characterized by X-ray powder diffraction and scanning electron microscopy and the electrochemical properties were investigated by the charge-discharge test. An initial discharge capacity of 149 mAh?g-1 was achieved for the LiEr0.02Fe0.98PO4/C composite cathode with a rate of 0.1 C. The electronic conductivity of Er doped LiFePO4/C was measured as 10-2 S?cm-1. The results indicated that erbium doping did not destroy the lattice structure of LiFePO4 and enlarge the lattice volume. These changes are beneficial to the improvement of the electrochemical performance of the LiFePO4 cathode.
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ISSN: 1005-0302
CN: 21-1315/TG
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