Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      20 July 2014, Volume 30 Issue 7 Previous Issue    Next Issue
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    Theoretical Investigation on Mechanical and Thermal Properties of a Promising Thermal Barrier Material: Yb3Al5O12
    Zhou Yanchun, Xiang Huimin, Feng Zhihai
    J. Mater. Sci. Technol., 2014, 30 (7): 631-638.  DOI: 10.1016/j.jmst.2014.06.007
    Abstract   HTML   PDF
    An investigation on the mechanical and thermal properties of Yb3Al5O12 is conducted by a combination of first-principles calculations and chemical bond theory calculation. Density functional theory (DFT) computations were performed for the structural, mechanical, and thermal properties, and the results are confirmed by chemical bond theory. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature is revealed. The full set of elastic constants and mechanical properties of Yb3Al5O12 are presented for the first time. The thermal expansion coefficient of Yb3Al5O12 is calculated to be 7.5 × 10-6 K–1 by chemical bond theory. In addition, the minimum thermal conductivity of Yb3Al5O12 is estimated to be 1.22 W m-1 K-1, and the origin of such low thermal conductivity is discussed. Our theoretical results highlight the potential of Yb3Al5O12 as a prospective thermal barrier coating material.
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    Density Functional Theory Study on the Oxidation of Hydrosilylated Silicon Nanocrystals
    Pi Xiaodong, Wang Rong, Yang Deren
    J. Mater. Sci. Technol., 2014, 30 (7): 639-643.  DOI: 10.1016/j.jmst.2014.01.012
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    As a leading surface modification approach, hydrosilylation enables freestanding silicon nanocrystals (Si NCs) to be well dispersed in a desired medium. Although hydrosilylation-induced organic layers at the NC surface may somehow retard the oxidation of Si NCs, oxidation eventually occurs to Si NCs after relatively long time exposure to air. We now investigated the oxidation of hydrosilylated Si NCs in the frame work of density functional theory (DFT). Three oxygen configurations that may be introduced by the oxidation of a Si NC are considered. It is found that a hydrosilylated Si NC is less prone to oxidation than a fully H-passivated Si NC in the point of view of thermodynamics. At the ground state, backbond oxygen (BBO) and hydroxyl (OH) hardly change the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a hydrosilylated Si NC. At the excited state, the decrease in the HOMO–LUMO gap induced by the introduction of doubly bonded oxygen (DBO) is more significant than that induced by the introduction of BBO or OH. We have correlated the changes in the optical absorption (emission) of a hydrosilylated Si NC after oxidation to those of the HOMO–LUMO gap at the ground state (excited state).
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    Tungsten Doped Indium Oxide Thin Films Deposited at Room Temperature by Radio Frequency Magnetron Sputtering
    Pan Jiaojiao, Wang Wenwen, Wu Dongqi, Fu Qiang, Ma Ding
    J. Mater. Sci. Technol., 2014, 30 (7): 644-648.  DOI: 10.1016/j.jmst.2013.10.023
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    Tungsten doped indium oxide (IWO) thin films were deposited on glass substrate at room temperature by radio frequency reactive magnetron sputtering. Chemical states analysis was carried out, indicating that valence states of element W in the films were W4+ and W6+. The effects of sputtering power and film thickness on the surface morphology, optical and electrical properties of IWO thin films were investigated. The IWO thin films had high transmittance in near infrared (NIR) spectral range. The resistivity, carrier mobility and carrier concentration owned their respective optimum values as sputtering power and thickness changed. The as-deposited IWO film with the minimum resistivity of 3.23 × 10-4 Ω cm was obtained at a sputtering power of 50 W, with carrier mobility of 27.1 cm2 V-1 s-1, carrier concentration of 7.15 × 1020 cm-3, average transmittance about 80% in visible region and above 75% in NIR region. It may meet the application requirement of high conductivity and transparency in NIR wavelength region.
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    Tensile Strength and Electrical Conductivity of Carbon Nanotube Reinforced Aluminum Matrix Composites Fabricated by Powder Metallurgy Combined with Friction Stir Processing
    Liu Z.Y., Xiao B.L., Wang W.G., Ma Z.Y.
    J. Mater. Sci. Technol., 2014, 30 (7): 649-655.  DOI: 10.1016/j.jmst.2014.04.016
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    A route combining powder metallurgy and subsequent friction stir processing was utilized to fabricate carbon nanotube (CNT) reinforced Al (CNT/Al) and 6061Al (CNT/6061Al) composites. Microstructural observations indicated that CNTs were uniformly dispersed in the matrix in both CNT/Al and CNT/6061Al composites. Mg and Si elements tended to segregate at CNT–Al interfaces in the CNT/6061Al composite during artificial aging treatment. The tensile properties of both the Al and 6061Al were increased by CNT incorporation. The electrical conductivity of CNT/Al was decreased by CNT addition, while CNT/6061Al exhibited an increase in electrical conductivity due to the Mg and Si segregation.
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    Preparation and Antibacterial Activity of Three-component NiFe2O4@PANI@Ag Nanocomposite
    Kooti M., Kharazi P., Motamedi H.
    J. Mater. Sci. Technol., 2014, 30 (7): 656-660.  DOI: 10.1016/j.jmst.2013.12.007
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    A new three-component and magnetically responsive NiFe2O4@PANI@Ag nanocomposite has been fabricated by coating of nickel ferrite, NiFe2O4, nanoparticles with polyaniline (PANI) and subsequent immobilization of silver nanoparticles onto the surface of polyaniline shell. The as-prepared nanocomposite has been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The saturation magnetization of the NiFe2O4 core decreases dramatically after coating with polyaniline and silver nanoparticles, however, the nanocomposite NiFe2O4@PANI@Ag can be still separated from solution media through magnetic decantation. The antibacterial activity of the synthesized nanocomposite was studied and compared with those of naked NiFe2O4, NiFe2O4@PANI and some standard antibacterial drugs.

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    Processing of B4C Particulate-reinforced Magnesium-matrix Composites by Metal-assisted Melt Infiltration Technique
    Yao Yantao, Chen Liqing
    J. Mater. Sci. Technol., 2014, 30 (7): 661-665.  DOI: 10.1016/j.jmst.2014.06.005
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    In fabricating magnesium-matrix composites, an easy and cost-effective route is to infiltrate the ceramic preform with molten Mg without any external pressure. However, a rather well wettability of molten Mg with ceramic reinforcement is needed for this process. In order to improve the wettability of the metal melt with ceramic preform during fabricating composites by metal melt infiltration, a simple and viable method has been proposed in this paper where a small amount of metal powder with higher melting point is added to the ceramic preform such that the surface tension of the Mg melt and the liquid–solid interfacial tension could be reduced. By using this method, boron carbide particulate-reinforced magnesium-matrix composites (B4C/Mg) have been successfully fabricated where Ti powder immiscible with magnesium melt was introduced into B4C preform as infiltration inducer. The infiltration ability of molten Mg to the ceramic preform was further studied in association with the processing conditions and the mechanism involved in this process was also analyzed.
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    Fluoride Conversion Coating on Biodegradable AZ31B Magnesium Alloy
    Yan Tingting, Tan Lili, Zhang Bingchun, Yang Ke
    J. Mater. Sci. Technol., 2014, 30 (7): 666-674.  DOI: 10.1016/j.jmst.2013.12.015
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    A fluoride conversion coating was successfully prepared on AZ31B magnesium alloy by chemical reaction in hydrofluoric acid. Morphologies, composition, bonding strength, corrosion properties, in vitro cytotoxicity and antibacterial properties of the coating were investigated, respectively. The scanning electron microscopy observations revealed a dense coating with some irregular pores. The thin-film X-ray diffraction analysis indicated that the coating was mainly composed of MgO and MgF2. The electrochemical impedance spectroscopy results showed that the fluoride conversion coating significantly improved the corrosion resistance of AZ31B. The hydroxyapatite formed on the surface of the fluoride coated AZ31B after being immersed in the simulated blood plasma indicated the good bioactivity of the material. The in vitro cytotoxicity test showed that the fluoride coated AZ31B alloy was not toxic to BMMSCs (human bone marrow-derived mesenchymal stem cells). It was also found that the fluoride coated AZ31B alloy had antibacterial capability.
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    In Vitro Study on Mg–Sn–Mn Alloy as Biodegradable Metals
    Zhen Zhen, Xi Tingfei, Zheng Yufeng, Li Li, Li Lugee
    J. Mater. Sci. Technol., 2014, 30 (7): 675-685.  DOI: 10.1016/j.jmst.2014.04.005
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    The mechanical properties, chemical properties and biocompatibility of Mg–3Sn–0.5Mn alloy were tested. A series of in vitro evaluations such as tensile test, static and dynamic immersion test, hemocompatibility test as well as cytotoxicity test were presented, with commercial magnesium alloy WE43 as the control. Mg–3Sn–0.5Mn alloy possesses suitable strength and superior ductility compared with WE43 and AZ31. Static immersion and dynamic degradation tests showed more uniform degradation with a more moderate rate for Mg–3Sn–0.5Mn alloy (0.34 mm/y in static condition and 0.25 mm/y in dynamic condition) compared with WE43 alloy (0.42 mm/y in static condition and 0.33 mm/y in dynamic condition) in Hank's solution. Blood compatibility evaluation suggested that Mg–3Sn–0.5Mn alloy had no destructive effect on erythrocyte and showed excellent anti-thrombogenicity to blood system. Besides, Mg–3Sn–0.5Mn alloy showed no inhibition effect to L929 metabolic activity and mild toxicity to vascular smooth muscle cell (VSMC) in preliminary cell viability assessment. By considering its excellent mechanical strength, corrosion resistance, low ion release rate and good biocompatibility, Mg–3Sn–0.5Mn alloy may be a promising economical candidate as biomedical implant material for load-bearing clinical applications in the future.
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    Synthesis and Characterization of a Novel Silver-Substituted Calcium Phosphate Cement
    Yu Tao, Gao Chengying, Ye Jiandong, Zhang Ming
    J. Mater. Sci. Technol., 2014, 30 (7): 686-691.  DOI: 10.1016/j.jmst.2014.03.005
    Abstract   HTML   PDF
    Antibacterial materials play an important role in clinical application, and silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. In this work, the amorphous calcium phosphate with silver substitution (Ag-ACP) was synthesized by chemical precipitation method, and the valence of silver in ACP was adjusted by temperature. The processed Ag-ACP was combined with slightly acidic compounds to form new calcium phosphate cement (CPC). Our results indicate that the valence of silver in CPC was adjusted successfully by chemical precipitation method and heat treatment. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrated that silver ion in CPC-1 and CPC-2 existed in Ag3PO4; after heat treatment of 460 °C, silver became more stable in CPC-3 and CPC-4. Silver in CPC-1 and CPC-2 exhibited better releasing property. After heat treatment at 460 °C, the amount of silver ion released from CPC decreased significantly. Besides, the antibacterial ability of Ag-CPC was adjusted by changing the valence of silver in Ag-CPC. Depending on the low valence of silver and good silver release, CPC-1 and CPC-2 exhibited better antibacterial activity. We believe that this study will motivate the development and applications of antibacterial CPC in bone tissue regeneration.
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    Influence of EDTA on Demineralization Rate of Dentine: Calcification Treatment in Root Canal Therapy
    Ji Yang, He Min, Chang Shijie, Zhang Xiaodong, Yang Huazhe
    J. Mater. Sci. Technol., 2014, 30 (7): 692-698.  DOI: 10.1016/j.jmst.2014.03.016
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    The aim of this study was to investigate the influence of ethylenediaminetetraacetic acid (EDTA) irrigation on demineralization rate of dentine located in the apical third of root canal walls. Teeth were divided into A and B two groups. In group A, all of the teeth was irrigated with EDTA and NaOCl (sodium hypochlorite), followed by cutting the apical third into slices longitudinally to examine the influence of EDTA on different portions of apical third of root canal. In group B, the apical third of a tooth was firstly cut into slices longitudinally, followed by coating the root canal walls with EDTA to in - situ observe the demineralization of dentine with different time. It was found that the influence of EDTA on root-canal was gradually increased from the apical to the upper end of the apical third for group A. In addition, the demineralization rate of dentine was remarkable in the first 25 min for group B. The diffusion of EDTA into root dentine would lead to potential damage to the dentine. Furthermore, demineralization rate curve was calculated.
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    Antibacterial Properties of Ti–6Al–4V– x Cu Alloys
    Ren Ling, Ma Zheng, Li Mei, Zhang Yu, Liu Weiqiang, Liao Zhenhua, Yang Ke
    J. Mater. Sci. Technol., 2014, 30 (7): 699-705.  DOI: 10.1016/j.jmst.2013.12.014
    Abstract   HTML   PDF
    Surgical implant-associated bacterial infection is becoming a serious clinical problem. A series of copper-bearing titanium alloy, Ti–6Al–4V– x Cu (x = 1, 3, 5 wt%), were fabricated in the present study in order to reduce the hazard of the bacterial infection problem by means of the strong antibacterial ability of Cu element. The metallography, X-ray diffraction, antibacterial ability, corrosion resistance and cytotoxicity of Ti–6Al–4V– x Cu alloys were preliminarily studied with comparison to the commercial medical Ti–6Al–4V alloy. The Ti–6Al–4V– x Cu alloys showed obvious antibacterial abilities with good corrosion resistance and cytocompatibility, and the antibacterial role was enhanced with increasing Cu content, which has significant potential for clinical applications as surgical implant materials.
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    Dwell and Normal Cyclic Fatigue Behaviours of Ti60 Alloy
    Yang Lina, Liu Jianrong, Tan Jun, Chen Zhiyong, Wang Qingjiang, Yang Rui
    J. Mater. Sci. Technol., 2014, 30 (7): 706-709.  DOI: 10.1016/j.jmst.2013.10.010
    Abstract   HTML   PDF
    An experimental study of dwell and normal cyclic fatigue behaviours was carried out using specimens from a Ti60 forging with a bimodal microstructure. Apparent decrease in the fatigue life was found under dwell fatigue condition as compared to that under normal cyclic condition. Strain produced in each cycle in dwell fatigued specimens was observed larger than that in its normal cyclic-fatigued counterparts. Interior crack initiation was found in most dwell fatigued specimens as compared to the subsurface crack initiation under normal cyclic fatigue condition. Flat and bright facets were found at crack initiation sites in both cases. The facet density is higher in dwell condition, which is consistent with the crystal orientation and Schmid factors analysis of α grains around secondary cracks using electron back-scattered diffraction (EBSD) methods. Dwell loading favours cleavage in α grains with their basal plane normals aligned no more than 15° to the loading axis, which may account for its lower fatigue life according to the present study.
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    Microstructure and Properties of 3.5 vol.% TiBw/Ti6Al4V Composite Tubes Fabricated by Hot-hydrostatic Extrusion
    Zhang Wencong, Jiao Xueyan, Yu Yang, Yang Jianlei, Feng Yangju
    J. Mater. Sci. Technol., 2014, 30 (7): 710-714.  DOI: 10.1016/j.jmst.2014.06.003
    Abstract   HTML   PDF
    Tubes of 3.5 vol.% TiB whiskers reinforced Ti6Al4V matrix composites (TiBw/Ti6Al4V) were successfully fabricated by a two-step hot-hydrostatic extrusion process: β extrusion at 1100 °C and subsequent near-β extrusion at 950 °C. The dimensions of tubes were about 7 mm in diameter and 2 mm in thickness. A refined basket-weave structure in Ti6Al4V matrix was achieved at ambient temperature after the extrusion process. Besides, the original network structure formed by TiB whiskers synthesized was broken, while the TiB whiskers were preferentially aligned in the extruding direction. Meanwhile, a fibrous texture was evolved finally, resulting from partial dynamic recrystallization during the β extrusion and the involvement of α phase during the near-β extrusion. The tensile and compressive tests results showed that both the strength and ductility of the tubes were significantly improved. In particular, the tubes exhibited good mechanical properties at elevated temperatures.
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    Microstructure Evolution and Tensile Properties of Ti3Al/Ni-based Superalloy Welded Joint
    Chen Bingqing, Xiong Huaping, Sun Bingbing, Tang Siyi, Guo Shaoqing, Zhang Xuejun
    J. Mater. Sci. Technol., 2014, 30 (7): 715-721.  DOI: 10.1016/j.jmst.2014.06.004
    Abstract   HTML   PDF
    In the present work, the dissimilar joining of a Ti3Al-based alloy to a Ni-based superalloy was attempted by gas tungsten arc (GTA) welding technology. Sound joints were successfully achieved by using a Cu–Ni alloy as filler material. According to X-ray energy dispersive spectroscopy and X-ray diffraction analysis results three transitional layers at the weld/Ti3Al interface were verified as follows: Ti2AlNb phase dissolved with Cu and Ni; Al(Cu,Ni)2Ti, (Cu,Ni)2Ti and (Nb,Ti) solid solution; Cu-rich phase and a complex multi-element phase. The In718/weld interface is characterized by solid solutions of Ni, Cu, Cr, Fe and Nb. The average tensile strength of the as-welded joints at room temperature is 163 MPa, and after a post–weld heat treatment it is increased slightly to 177 MPa. The fracture occurred at the surfacial layer of the joined Ti3Al base alloy, indicating that the Ti2AlNb layer dissolved with Cu and Ni is the weak link of the Ti3Al/In718 joint.
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    Characterization, Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr55Cu30Ni5Al10 Bulk Metallic Glass
    Chen Haiyan, Cao Jian, Song Xiaoguo, Liu Jiakun, Feng Jicai
    J. Mater. Sci. Technol., 2014, 30 (7): 722-730.  DOI: 10.1016/j.jmst.2013.09.020
    Abstract   HTML   PDF
    The composition of oxide film of Zr55Cu30Ni5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.
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ISSN: 1005-0302
CN: 21-1315/TG
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