Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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The journal has been awarded the excellent periodical in China, and its articles are covered by SCI, EI, CA, SA, JST, RJ, CSA, MA, EMA, AIA etc., PASCAL web. ISI web of Science,SCOPUS.

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      12 November 2012, Volume 28 Issue 12 Previous Issue    Next Issue
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    Thin Film and Coatings
    A Galvanostatic Modeling for Preparation of Electrodeposited Nanocrystalline Coatings by Control of Current Density
    Ali Mohammad Rashidi
    J. Mater. Sci. Technol., 2012, 28 (12): 1071-1076. 
    Abstract   HTML   PDF

    The correlation between the grain size of electrodeposited coatings and the current densities was modeled by considering galvanostatic conditions. In order to test the model by experimental results, nanocrystalline (NC) nickel samples were deposited at different current densities using a Watts bath. The grain size of the deposits was evaluated by X-ray diffraction (XRD) technique. Model predictions were validated by finding a curve being the best-fit to the experimental results which were gathered from literature for different NC coatings in addition to those data measured in this research for NC nickel coatings. According to our model, the variation of grain size with the reciprocal of the current density follows a power law. A good agreement between the experimental results and model predictions was observed which indicated that the derived analytical model is applicable for producting the nanocrystalline electrodeposits with the desired grain size by controling current density.

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    Mechanical and Barrier Properties of Epoxy/Ultra-short Glass Fibers Composite Coatings
    Yongsheng Hao, Fuchun Liu, En-Hou Han
    J. Mater. Sci. Technol., 2012, 28 (12): 1077-1084. 
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    Epoxy coatings containing different volume fractions of ultra-short glass fibers were prepared successfully. Ultra-short glass fiber not only can improve the hardness, adhesion of the coating, and glass transition temperature (Tg), but also can decrease the coefficient of thermal expansion (CTE) of the coating. Electrochemical impedance spectroscopy (EIS) was used to evaluate the barrier properties of the coatings containing different volume fractions of ultra-short glass fibers. The EIS results showed that the coating had the best barrier property when it contained 20% (volume fraction) ultra-short glass fibers. The functions of the ultra-short glass fibers in epoxy coating are two-fold: first, they can improve the coating mechanical properties as reinforcement materials; second, they parallel to the substrate and inhibit the corrosive medium to pass through the coating.

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    Iron and Steel
    Microstructural Characterization and Mechanical Properties of Powder Metallurgy Dual Phase Steel Preforms
    K. Mahesh, S. Sankaran, P. Venugopal
    J. Mater. Sci. Technol., 2012, 28 (12): 1085-1094. 
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    In order to improve the mechanical properties of powder metallurgy (P/M) ferrite-pearlite steel, a dual phase (DP) ferrite{martensite steel was produced through intercritical annealing of sintered P/M preforms. Microstructures of the sintered and DP steels were examined with optical, scanning and transmission electron microscopes. Mechanical properties were evaluated through hardness measurements and compression tests. Microstructural studies revealed that sintered steel contained polygonal ferrite{pearlite while the DP steel contained polygonal, lath and acicular ferrite along with lath-type martensite as microstructural constituents. In DP steels, with increasing mean preform density, the microstructure contained fine and continuous network
    of martensite colonies with minimum porosity. The work hardening rate vs plastic strain plots (Jaoul-Crussard analysis) of both the steels revealed typical three stage deformation behaviour for low and high mean preform densities. Compression tests revealed that, DP P/M steel displayed higher strength-plasticity combination than the sintered steel.

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    Characterizations of Dynamic Strain-induced Transformation in Low Carbon Steel
    Luhan Hao, Mingyue Sun, Namin Xiao, Dianzhong Li
    J. Mater. Sci. Technol., 2012, 28 (12): 1095-1101. 
    Abstract   HTML   PDF

    Dynamic strain-induced transformation of the low carbon steel Q235 at 770 oC and 850 oC leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries (HAGBs) are dominant in both of the deformation induced microstructures occurring below and above Ae3, with only a few low angle grain
    boundaries (LAGBs) existing in the grain interiors. It implies that the dynamic strain-induced transformation (DSIT) happens above and below Ae3 temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization (CDRX) of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q235 steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.

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    Mechanical and Functional Properties of Materials
    Effect of Compression on the Crystallization Behavior and Corrosion Resistance of Al86Ni9La5 Amorphous Alloy
    Yan Liu, Weimin Wang, Hongdi Zhang, Haijian Ma, Bang An
    J. Mater. Sci. Technol., 2012, 28 (12): 1102-1108. 
    Abstract   HTML   PDF

    The effect of compression on the crystallization behavior and corrosion resistance of Al86Ni9La5 amorphous ribbons was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electrochemistry test. The XRD and TEM results reveal that the compressed Al86Ni9La5 ribbons spun with the circumferential speed (R) of 29.3 m/s are in fully amorphous state; however, the compressed ribbons spun with R=14.7 m/s have crystalline phases embedded in the amorphous matrix. The SEM images indicate that after compression, the toughness of the ribbons increases. Electrochemical results show that the compression decreases the stability of the passive film of the Al86Ni9La5 amorphous ribbons, because of the compression-introduced free volume, shear bands and crystalline phases; meanwhile, with R=14.7 m/s, the compression-induced crystalline phases in the Al86Ni9La5 ribbons increase the corrosion potential.

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    Locating Malleable Bulk Metallic Glasses in Zr{Ti{Cu{Al Alloys with Calorimetric Glass Transition Temperature as an Indicator
    Qiang He, Jian Xu
    J. Mater. Sci. Technol., 2012, 28 (12): 1109-1122. 
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    We defined the plastic deformability under constrained loading conditions as malleability for bulk metallic glass (BMG) materials. Quaternary Zr-Ti-Cu-Al alloys in the Zr-rich composition range are selected to investigate the compositional dependence of malleability assessed by bending testing and glass transition temperature (Tg). As indicated, increasing the Al or Cu concentration in the alloys leads to the rise of Tg. The Zr61Ti2Cu25Al12 (ZT1) and Zr61.6Ti4.4Cu24Al10 (ZT3) alloys exhibit an optimal combination of lower Tg and higher glass-forming ability. The malleable BMGs such as ZT1 manifests two characters during deformation, the stable propagation of a single shear band indicated by large shear offsets and easy proliferation of shear bands. With increasing the Tg of BMG, the yield strength σy, Young0s modulus and shear modulus simultaneously increase as well, while the Poisson's ratio decreases. The σyof ZT1 BMG is about 1680 MPa in compression and 1600 MPa in tension. In tensile loading, no any visible plasticity appears even when the strain rate increases up to the order of magnitude of 10-1 s-1. In consistent with the Tg, malleability of Zr-Ti-Cu-Al BMGs manifests significant compositional dependence. The malleable BMG is associated with lower Tg, as well as lower shear modulus or higher Poisson's ratio, which can be understood on the basis of the correlation of Tg with shear energy barrier in metallic glass. Thus, the calorimetric Tg can be used as an indicator to screen malleable BMG-forming composition, with advantage of experimental accessibility.

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    Anodic Oxidation on Structural Evolution and Tensile roperties of Polyacrylonitrile Based Carbon Fibers with Different Surface Morphology
    Zhaorui Li, Jianbin Wang, Yuanjian Tong, Lianghua Xu
    J. Mater. Sci. Technol., 2012, 28 (12): 1123-1129. 
    Abstract   HTML   PDF

    Polyacrylonitrile (PAN) based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size (La) of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing (d002) increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m2. The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.

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    Effect of Titania Additive on Structural and Mechanical Properties of Alumina{Fluorapatite Composites
    Awatef Guidara, Kamel Chaari, Jamel Bouaziz
    J. Mater. Sci. Technol., 2012, 28 (12): 1130-1136. 
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    Mechanical properties of alumina-fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600 °C. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500 °C for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2, the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate (Al2O3-TiO2:Al2TiO5). The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.

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    Effect of (Ba0.6Sr0.4)TiO3 (BST) Doping on Dielectric Properties of CaCu3Ti4O12 (CCTO)
    I. Norezan, A.K. Yahya, M.K. Talari
    J. Mater. Sci. Technol., 2012, 28 (12): 1137-1144. 
    Abstract   HTML   PDF

    The effect of (Ba0.6Sr0.4)TiO3(BST) addition on dielectric properties of CaCu3Ti4O12 (CCTO) ceramic was investigated. Ceramic samples with the chemical formula (1–x)CaCu3Ti4O12 + x(Ba0.6,Sr0.4)TiO3 (x=0, 0.05, 0.1, and 0.2) were synthesized from high purity oxide powders by the conventional solid-state synthesis method. X-ray diffraction (XRD) analysis showed the existence of BST as a secondary phase alongside CCTO. Scanning electron microscopy (SEM) investigation showed a slight decrease in grain size of doped CCTO samples. Density measurements showed that porosity content increased with increasing BST addition indicating low densification due to high melting point secondary phase addition. Dielectric constant of undoped CCTO (x=0) showed lack of stability with frequency which dropped drastically between 104 and 105 Hz and accompanied by high dielectric loss. Addition of BST into CCTO caused the dielectric constant to slightly decrease but improved stability with frequency compared to the undoped sample. The decrease in dielectric constant of doped CCTO samples was suggested to be partly due to the decrease in average grain size and increase in porosity with BST addition. Nevertheless, a high value of dielectric constant was still maintained around ~104 range for all doped samples. The dielectric loss (tanδ) of all BST-doped samples was lower than that of pure CCTO sample at the frequency range of 103 to 105 Hz probably due to the increase of grains boundary resistivity. The activation energy of grains boundary (Egb) showed higher values as compared to the activation energy of grains (Eg) for all samples and conforms to the internal barrier layer capacitor (IBLC) model.

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    Dielectric and Electrical Transport Properties of the Fe3+-doped CaCu3Ti4O12
    Zhi Yang, Yue Zhang, Guang You, Kun Zhang, Rui Xiong, Jing Shi
    J. Mater. Sci. Technol., 2012, 28 (12): 1145-1150. 
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    CaCu3-xFexTi4O12 (x=0, 0.015, 0.03, 0.045, 0.06) ceramics were synthesized by sol-gel method. The electrical conduction and dielectric measurements show that the doping of a very small amount of Fe3+ ions greatly reduces the low-frequency dielectric constants and leakage, and enhances grain resistivity. For the doped samples, the appearance of the strong low-frequency peaks in the spectra of dielectric loss confirms that the doping of Fe3+ ions induces the contact-electrode effect on ceramic surface. These great changes of electrical properties may originate from the reduced amount of oxygen vacancies by doping Fe3+.

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    Fabrication and Properties of Porous Si3N4 Ceramic with High Porosity
    Xiangming Li, Litong Zhang, Xiaowei Yin
    J. Mater. Sci. Technol., 2012, 28 (12): 1151-1156. 
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    A novel process combining oxidation-bonding and sintering was developed to fabricate porous Si3N4 ceramic with high porosity. After sintering at 1800 °C, the SiO2 in porous Si3N4 ceramic transforms into Si2N2O because of the reaction of SiO2 and Si3N4. Due to the reaction of SiO2 and carbon, the porosity of porous Si3N4 ceramic increases obviously from 40.2% to 76.8% with the weight decreasing by 35.6%. As the porosity increases, the dielectric constant and loss of the porous Si3N4 ceramic decrease obviously from 3.08 to 1.61 and from 3.70×10-3 to 0.74×10-3, but due to the production of Si2N2O whose mechanical properties are much higher than SiO2 and the increase of the bonding strength among Si3N4 particles, the flexural strength and the fracture toughness of the porous Si3N4 ceramic decrease from 55 to 39 MPa and from 0.7 to 0.5 MPa·m1/2, respectively, but its Vickers hardness increases from 1.2 to 1.3 GPa.

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    Corrosion Behavior of Mg-Zn-Y Alloy with Long-period Stacking Ordered Structures
    Jinshan Zhang, Jidong Xu, Weili Cheng, Changjiu Chen, Jingjing Kang
    J. Mater. Sci. Technol., 2012, 28 (12): 1157-1162. 
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    Mg-Zn-Y alloys with long-period stacking ordered structures were prepared by an ingot casting method. The corrosion performance of Mg-Zn-Y alloys was studied by combining gas-collecting test, immersion test and electrochemical measurements in order to determine the corrosion rate and mechanism of the alloys. The results showed that the volume fraction of Mg12YZn phase increased and the shape of the Mg12YZn phase changed from discontinuous to continuous net-like with increasing Zn and Y content. The corrosion rate of the alloys greatly depended on the distribution and volume fraction of the Mg12YZn phase. Corrosion products appeared at the junction of Mg phase and Mg12YZn phase, indicating that the Mg12YZn phase accelerated 
    galvanic corrosion of Mg matrix. Mg97Zn1Y2 alloy shows the lowest corrosion rate due to the continuous distribution of Mg12YZn phase.

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    Microstructure and Properties of Joint Interface of Semisolid Stirring Brazing of Composites
    Huibin Xu, Bofang Zhou, Changhua Du, Quanxiang Luo, Hongyou Chen
    J. Mater. Sci. Technol., 2012, 28 (12): 1163-1168. 
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    Stirring assisted brazing of SiCp/A356 composites in air was investigated. A stirring was applied on one of the samples to be bonded at 455 °C during brazing. The filler metal was extruded and impacted intensively on the two surfaces of the base materials during stirring. It can be found that oxide film on the surface of the composites can be disrupted and removed through the observation by scanning electron microscopy (SEM). The metallurgical bonds formed between the filler metal and the base materials. However, continuous residual oxide film was found at bottom joint interface, which limited the lift of joint strength. A stirring was applied once more after the samples were continuously heated up to 470 and 500 °C, respectively. At this time, residual oxide film after the first of stirring can be broken by once more stirring. The bonds are mainly composed of a new alloy, which have a higher content of aluminum and are free of continuous oxide film, showing higher shear strength of 113 MPa than that of the base materials.

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    Regular Paper
    Investigation of the Heterogeneous Nucleation on Fractal Surfaces
    Meng Wang, Ying Zhang, Haoyong Zheng, Xin Lin, Weidong Huang
    J. Mater. Sci. Technol., 2012, 28 (12): 1169-1174. 
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    Classical theory of heterogeneous nucleation has been developed with an implied hypothesis of smooth substrate surfaces; however, morphologies of any real substrate surfaces are generally complicated and demonstrate fractal characteristics. In this paper, the wettability between the embryo and the fractal substrate surface was discussed, and heterogeneous nucleation behaviors were theoretically analyzed. The result shows that the roughness factor of a fractal surface varies with the scale of the embryo. As a result, the fractal character of the substrate surface has important effects on heterogeneous nucleation behaviors. It has been shown that the energy barrier for heterogeneous nucleation of a non-wetting phase on a fractal rough surface increases with increasing fractal dimensions, and both the critical nucleus radius and the nucleation energy barrier decrease with increasing fractal dimensions for heterogeneous nucleation of a wetting phase on the fractal rough surface. For a non-wetting system, the critical nucleus radius shows a slight shift with changes of the intrinsic wetting angle, but for a wetting system, the critical nucleus radius shows an obvious change with decreasing intrinsic wetting angle, thus imposes a stronger effect on the heterogeneous nucleation behaviors.

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ISSN: 1005-0302
CN: 21-1315/TG
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