Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
Impact factor:6.155

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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      20 November 2017, Volume 33 Issue 11 Previous Issue    Next Issue
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    Orginal Article
    Acoustic properties of closed-cell aluminum foams with different macrostructures
    Xia Xingchuan, Zhang Zan, Zhao Weimin, Li Chong, Ding Jian, Liu Chenxi, Liu Yongchang
    J. Mater. Sci. Technol., 2017, 33 (11): 1227-1234.  DOI: 10.1016/j.jmst.2017.07.012
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    As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function integration materials, the application of closed-cell aluminum foams has been restricted greatly in acoustic fields due to the difficulty of sound wave penetration. It was reported that closed-cell foams with macrostructures have important effect on the propagation of sound waves. To date, the relationship between macrostructures and acoustic properties of commercially pure closed-cell aluminum foams is ambiguous. In this work, different perforation and air gap types were designed for changing the macrostructures of the foam. Meanwhile, the effect of macrostructures on the sound absorption coefficient and sound reduction index were investigated. The results showed that the foams with half-hole exhibited excellent sound absorption and sound insulation behaviors in high frequency range (>2500 Hz). In addition, specimens with air gaps showed good sound absorption properties in low frequency compared with the foams without air gaps. Based on the experiment results, propagation structural models of sound waves in commercially pure closed-cell aluminum foams with different macrostructures were built and the influence of macrostructures on acoustic properties was discussed.

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    Structural evolution of Al-8%Si hypoeutectic alloy by ultrasonic processing
    Wang J.Y., Wang B.J., Huang L.F.
    J. Mater. Sci. Technol., 2017, 33 (11): 1235-1239.  DOI: 10.1016/j.jmst.2017.07.018
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    High intensity power ultrasound was respectively introduced into three different solidification stages of Al-8%Si hypoeutectic alloy, including the fully liquid state before nucleation, the nucleation and growth process of primary α(Al) phase and L → (Al) + (Si) eutectic transformation period. It is found that both the primary α(Al) phase and (Al + Si) eutectic structure were refined by different degrees with various growth morphologies depending on the ultrasonic treatment stage. Based on the experimental results, the cavitation-induced nucleation due to the high undercooling caused by the collapse of tiny cavities was proposed as the major reason for refining the primary α(Al) phase. Meanwhile, obvious eutectic morphological change was observed only when ultrasound was directly introduced in the eutectic transformation stage, in which typical divorced eutectics and (Al + Si) eutectic cells with symmetrical flower shape were formed at the top of the alloy sample. The introduction of ultrasound in each solidification stage also improves the yield strength of Al-8% Si alloy to a diverse extent.

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    Microstructure and Thermal Conductivity of As-Cast and As-Solutionized Mg-Rare Earth Binary Alloys
    Zhong Liping, Peng Jian, Sun Song, Wang Yongjian, Lu Yun, Pan Fusheng
    J. Mater. Sci. Technol., 2017, 33 (11): 1240-1248.  DOI: 10.1016/j.jmst.2016.08.026
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    The microstructure and thermal conductivity of four groups of Mg-rare earth (RE) binary alloys (Mg-Ce, Mg-Nd, Mg-Y and Mg-Gd) in as-cast and as-solutionized states were systematically studied. Thermal conductivity was measured on a Netzsch LFA457 using laser flash method at room temperature. Results indicated that for as-cast alloys, the volume fraction of second phases increased with the increase of alloying elements. After solutionizing treatment, a part or most of second phases were dissolved in α-Mg matrix, except for Mg-Ce alloys. The thermal conductivity of as-cast and as-solutionized Mg-RE alloys decreased with the increase of concentrations. The thermal conductivity of as-solutionized Mg-Nd, Mg-Y and Mg-Gd alloys was lower than that of as-cast alloys. Thermal conductivity of as-solutionized Mg-Ce alloys was higher than that of as-cast alloys, because of the elimination of lattice defects and fine dispersed particles during solutionizing treatment. Different RE elements have different influences on the thermal conductivity of Mg alloys in the following order: Ce < Nd < Y < Gd. Ce has the minimum effect on thermal conductivity of Mg alloys, because of the very low solubility of Ce in the α-Mg matrix. The variations in the atomic radius of the solute elements with Mg atom (Δr), valence, configuration of extra-nuclear electron of the solute atoms, and the maximum solid solubility of elements in the α-Mg matrix were suggested to be the main reasons for the differences in thermal conductivity of resulting Mg-RE alloys.

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    Improving mechanical properties of age-hardenable Mg-6Zn-4Al-1Sn alloy processed by double-aging treatment
    Zhu treatmentShaozhen, Luo Tianjiao, Yang Yuansheng
    J. Mater. Sci. Technol., 2017, 33 (11): 1249-1254.  DOI: 10.1016/j.jmst.2017.07.021
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    Microstructure and mechanical properties of a new high-strength Mg-6Zn-4Al-1Sn alloy were investigated. Microstructure of the as-cast Mg alloy exhibited partially divorced characteristics. The dendritic structure of the Mg-6Zn-4Al alloy was significantly refined with the addition of 1% (in weight) Sn, but Mg2Sn phases were not formed. In addition, an icosahedral quasi-crystal phase was formed in the as-cast Mg-6Zn-4Al-1Sn alloy. It was found that after the double-aging treatment through two different heat treatments on the Mg-6Zn-4Al-1Sn alloy, the precipitates were finer and far more densely dispersed in the matrix compared with single-aged counterpart, resulting in a significant improvement in tensile strength with yield strength, ultimate tensile strength and elongation of 175 MPa, 335 MPa and 11%, respectively.

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    Finite element modelling on microstructure evolution during multi-pass hot compression for AZ31 alloys using incremental method
    Jin Zhaoyang, Yin Kai, Yan Kai, Wu Defeng, Liu Juan, Cui Zhenshan
    J. Mater. Sci. Technol., 2017, 33 (11): 1255-1262.  DOI: 10.1016/j.jmst.2017.10.008
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    Based on the principle of piecewise linearization, the incremental forms of microstructure evolution models were integrated into the thermo-mechanical coupled finite element (FE) model to simulate non-linear microstructure evolution during multi-pass hot deformation. This is an unsteady-state deformation where dynamic recrystallization (DRX), meta-dynamic recrystallization (MDRX), static recrystallization (SRX) and grain growth (GG) take place during hot deformation or deformation interval. The distributions of deformation and microstructure for cylindrical AZ31 sample during single-pass and double-pass hot compressions were quantitatively calculated and compared with the metallographic observation. It is shown that both the deformation and microstructure are non-uniformly distributed due to the presence of friction between the die and the flat end of sample. The average grain size and its standard deviation under the double-pass hot compression are slightly smaller than those under single-pass compression. The simulated average grain sizes agree well with the experiments, which validates that the developed FE model on the basis of incremental forms of microstructure evolution models is reasonable.

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    Corrosion resistance of a superhydrophobic micro-arc oxidation coating on Mg-4Li-1Ca alloy
    Cui Lan-Yue, Liu Han-Peng, Zhang Wen-Le, Han Zhuang-Zhuang, Deng Mei-Xu, Zeng Rong-Chang, Li Shuo-Qi, Wang Zhen-Lin
    J. Mater. Sci. Technol., 2017, 33 (11): 1263-1271.  DOI: 10.1016/j.jmst.2017.10.010
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    A micro-arc oxidation (MAO)/zinc stearate (ZnSA) composite coating was fabricated via MAO processing and subsequent sealing with electrodeposition of a superhydrophobic ZnSA. The surface morphologies, chemical composition and corrosion resistance of the coatings were investigated using field-emission scanning electron microscopy, Fourier transform infrared, X-ray diffraction and electrochemical and hydrogen evolution measurements. Results indicated that the MAO coating was efficiently sealed by the following superhydrophobic ZnSA coating. The MAO/ZnSA composite coating significantly enhanced the corrosion resistance of Mg alloy Mg-4Li-1Ca due to its superhydrophobic function. Additionally, corrosion mechanism was suggested and discussed for the composite coating.

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    Deformation behavior of Al-rich metallic glasses under nanoindentation
    Guo Hui, Jiang Chuanbin, Yang Baijun, Wang Jianqiang
    J. Mater. Sci. Technol., 2017, 33 (11): 1272-1277.  DOI: 10.1016/j.jmst.2016.10.014
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    To clarify the deformation behavior of Al-rich metallic glasses (MGs), two kinds of Al-rich MGs (i.e. bulk and ribbon samples) with different frozen-in excess volume have been analyzed under nanoindentation. It was found that, with the decrease of frozen-in excess volume, the serration behavior becomes inconspicuous together with the increase of hardness. Further, shear transformation zones (STZs), related to the occurrence of shear banding, have been evaluated by different methods: the cooperative shearing model (CSM), the rate-jump method (RJM) and the dynamic-mechanical response (DMR). In contrast, the STZ volumes, calculated by the RJM, increase from 2.77 nm3 in the bulk to 3.59 nm3 in the ribbon, which are in good agreement with 2.60 nm3 obtained from the icosahedral supercluster medium-range order structure model in Al-rich MGs. This result reflects that an intrinsic correlation exists between the formation of STZs and the medium-range orders (MROs). Moreover, the variation trend of the STZ volume was analyzed in terms of the frozen-in excess volume content.

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    Role of late transition metals on pitting resistance of Zr-Ti-(Cu, Ni, Co)-Al bulk metallic glasses in 0.6 M NaCl aqueous solution
    Li Yu, Xu Jian
    J. Mater. Sci. Technol., 2017, 33 (11): 1278-1288.  DOI: 10.1016/j.jmst.2017.04.010
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    Four quanternary Zr-based bulk metallic glasses (BMGs) were selected, including the Zr46Ti2Cu45Al7, Zr61Ti2Cu25Al12, Zr55Ti4Ni22Al19 and Zr55Ti2Co28Al15, due to their robust glass-forming ability and containing a single species of late transition metal (LTM) in compositions. Their pitting resistances in 0.6 M NaCl aqueous solution were investigated to examine the role of LTM elements in the alloys, with electrochemical measurements, surface morphology observation and x-ray photoelectron spectrometry analysis. It is shown that in comparision with two Cu-bearing BMGs, Zr55Ti4Ni22Al19 and Zr55Ti2Co28Al15 BMGs exhibited significantly superior resistance to pitting. Zr61Ti2Cu25Al12, Zr55Ti4Ni22Al19 and Zr55Ti2Co28Al15 BMGs manifested distinct passivation behaviour, because of the formation of surface passive film mainly comprising of ZrO2, TiO2 and Al2O3. However, no significant differences in the electrochemical resistive properties and thicknesses of passive films were found between Zr61Ti2Cu25Al12 and Zr55Ti4Ni22Al19 BMGs. Nevertheless, at the passive film/metal interface, copper enrichment took place in Zr61Ti2Cu25Al12, whereas the nickel was slightly deficient at the interface in Zr55Ti4Ni22Al19. During pitting propagation, selective dissolution of the zirconium, titanium and aluminum over the copper took place in Zr61Ti2Cu25Al12, but it was not the case in Zr55Ti4Ni22Al19. For the two Cu-bearing BMGs, reduction of passive base metal elements in composition resulted in local selective dissolution, even absence of the passivation.

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    Microstructure and Mechanical Properties of Fiber Laser Welded GH3535 Superalloy
    Yu Kun, Jiang Zhenguo, Li Chaowen, Chen Shuangjian, Tao Wang, Zhou1 Xingtai, Li Zhijun
    J. Mater. Sci. Technol., 2017, 33 (11): 1289-1299.  DOI: 10.1016/j.jmst.2016.11.026
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    As a primary material of the thorium molten salt reactor (TMSR) that is a suitable candidate reactor of the Generation IV nuclear reactors, GH3535 superalloy was successfully welded. The effect of laser beam welding (LBW) on microstructure evolution of fusion zone (FZ) and heat affected zone (HAZ), such as element segregation, precipitate behavior and grain evolution, was investigated. The microhardness and tensile properties were tested and discussed. The results of microstructure evolution showed that a number of fine M6C-γ eutectic phases precipitated at solidification grain boundaries and interdendritic region in FZ. Compared to base metal zone (BMZ), the grain size of HAZ has no obvious change. While a few of M6C-γ eutectic phases were observed in partially melted zone (PMZ) of HAZ. The results of microhardness indicated that the hardness of FZ was higher than that of HAZ and BMZ. The results of tensile test showed that the ultimate tensile strength of joints at room temperature, 650 and 700 °C were 98%, 97% and 99% of that of BM, respectively. All the tensile specimens of joints failed in BMZ rather than in PMZ where M6C carbides had been transformed into M6C-γ eutectic phases.

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    Effect of Solution Annealing on Microstructure and Mechanical Properties of a Ni-Cr-W-Fe Alloy
    Ou Meiqiong, Ma Yingche, Hao Xianchao, Wan Baifang, Liang Tian, Liu Kui
    J. Mater. Sci. Technol., 2017, 33 (11): 1300-1307.  DOI: 10.1016/j.jmst.2016.06.026
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    The effect of solution annealing on the microstructure and mechanical properties of a Ni-Cr-W-Fe alloy developed for advanced 700 °C ultra-supercritical power plants was investigated. Test samples in this study were subjected to different solution treatments and the same aging treatment (at 760 °C for 1 h). When solution annealing temperature was elevated from 1020 °C to 1150 °C, the stress-rupture life at 750 °C/320 MPa was increased from 60 h to 300 h, the stress-rupture elongation was enhanced from 12% to 17%, and the elongation of the tensile at 750 °C was improved from 11% to 24%. All tensile and stress-rupture samples displayed an intergranular dimple mixed fracture. Intergranular micro-cracks had a great relationship with the morphology of grain boundary carbides. Most carbides retained the morphology of globular shape and continuous thin plate. After tensile and stress-rupture tests, a few carbides were converted into lamellar. The results showed that intergranular micro-cracks were easier to form at continuous thin plate carbides than at globular shape carbides. Lamellar carbides hardly caused the nucleation of micro-cracks. Besides, grain boundaries sliding and elements diffusion during stress-rupture tests led to the formation of precipitate free zones, which accelerated the extension of micro-cracks and influenced the stress-rupture life.

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    Effects of Re on surface eutectic formation for Ni-base single crystal superalloys during directional solidification
    Cao Liang, Zhou Yizhou, Jin Tao, Sun Xiaofeng
    J. Mater. Sci. Technol., 2017, 33 (11): 1308-1313.  DOI: 10.1016/j.jmst.2017.03.017
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    Effects of Re on the formation of surface eutectics have been investigated by using Ni-base single crystal superalloys with different Re additions. It was found that Re promotes the segregation of Al and Ta to the eutectic melt, leading to an increase of the surface and internal eutectics. In addition, the addition of Re also increased the freezing range, the local solidification time, and the permeability of the dendritic network within the mushy zone. These factors ultimately promoted the outflow of the interdendritic residual liquid with the action of solidification shrinkage, and led to the formation of more surface eutectics. In contrast, the addition of Re had no obvious influence on the surface eutectic microstructures.

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    Nano-TiO2 Decorated Radial-Like Mesoporous Silica: Preparation, Characterization, and Adsorption-Photodegradation Behavior
    Qian Tingting, Yin Xiaoping, Li Jinhong, Nian Hong’en, Xu Hui, Deng Yong, Wang Xiang
    J. Mater. Sci. Technol., 2017, 33 (11): 1314-1322.  DOI: 10.1016/j.jmst.2016.09.013
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    Supported nanocrystalline TiO2 with a diameter of 15-30 nm was prepared from previously synthesized radial mesoporous silica (RMS) by a post-synthesis method. In addition, their adsorption-photocatalytic activity toward the degradation of methylene blue (MB) was determined. RMS was tailor-made with the main template of CTAB and the SiO2 precursor of TEOS through a facile self-assembly process. The structural, morphological and textural properties of the well-designed TiO2/RMS samples were characterized. The RMS structure was retained after loading TiO2, but its surface area and pore diameter decreased as a result of partial pore blocking. The removal activity of MB for TiO2/RMS was significantly higher than that of commercial TiO2 nanoparticles. The optimal TiO2 loading (20 wt%) on the support could achieve the complete removal of MB within 70 min. The prepared TiO2/RMS particles can be easily separated and display good durability after six reaction cycles.

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    Suppressing Al2O3 nanoparticle coarsening and Cu nanograin growth of milled nanostructured Cu-5vol.%Al2O3 composite powder particles by doping with Ti
    Zhou Dengshan, Geng Hongwei, Zeng Wei, Zhang Deliang, Kong Charlie, Munroe Paul
    J. Mater. Sci. Technol., 2017, 33 (11): 1323-1328.  DOI: 10.1016/j.jmst.2017.03.010
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    Both the coarsening of Al2O3 nanoparticles and the growth of Cu nanograins of mechanically milled nanostructured Cu-5vol.%Al2O3 composites with, and without, trace amounts of Ti during annealing at 973 K for 1 h were investigated. It was found that doping with a small amount of Ti (e.g. 0.2 wt%) in a nanostructured Cu-5vol.%Al2O3 composite effectively suppressed the coarsening of Al2O3 nanoparticles during exposure at this temperature. Further, the Ti addition also prevented the concomitant abnormal growth of the copper grains normally caused by the coarsening of the Al2O3 nanoparticles. Energy dispersive X-ray spectroscopy analysis of the Al2O3 nanoparticles in the annealed Cu-5vol.%Al2O3-0.2wt%Ti sample suggested that the Ti atoms either diffused into the Al2O3 nanoparticles or segregated to the Cu/Al2O3 interfaces to form Ti-doped Al2O3 nanoparticles, which was more stable than Ti-free Al2O3 nanoparticles during annealing at high homologous temperatures.

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    Fabrication and optimization of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ electrode for symmetric solid oxide fuel cell with zirconia based electrolyte
    Xu Na, Zhu Tenglong, Yang Zhibin, Han Minfang
    J. Mater. Sci. Technol., 2017, 33 (11): 1329-1333.  DOI: 10.1016/j.jmst.2017.03.012
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    La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) was applied as both anode and cathode for symmetrical solid oxide fuel cells (SSOFCs) with zirconia based electrolyte. The cell with LSCFN electrode was fabricated by tape-casting and screen printing. Fabrication process was optimized firstly by comparing co-sintering and separate-sintering of electrode and electrolyte. To further improve the LSCFN electrode properties, oxygen ionic conductor of Gd0.1Ce0.9O2-δ (GDC) was added into the LSCFN electrode. The preferred composition of LSCFN-GDC composite electrode was found to be 1:1 in weight ratio with polarization resistance of 0.16 Ω cm2 at 800 °C. The maximum power densities of LSCFN-GDC||GDC/YSZ/GDC||LSCFN-GDC tested in H2 and CH4 with 3% H2O were 395 mW cm-2 and 124 mW cm-2 at 850 °C, respectively, which were much higher than that of LSCFN||GDC/YSZ/GDC||LSCFN cells at same condition, possibly due to the extension of the triple phase boundary induced by the addition of GDC. The cell showed reasonable stability using H2 and CH4 with 3% H2O as fuels and no significant power output degradation was observed after total 200 h operation.

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    Air stable Fe nanostructures with high magnetization prepared by reductive annealing
    Liu Yanhua, Bian Baoru, Hu Chunfeng, Yi Pengpeng, Du Juan, Xia Weixing, Zhang Jian, Yan Aru, Li Ying, Ping Liu J.
    J. Mater. Sci. Technol., 2017, 33 (11): 1334-1338.  DOI: 10.1016/j.jmst.2017.04.007
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    Monodispersed Fe nanospindles and nanoparticles were successfully synthesized through environment-friendly reductive annealing β-FeOOH nanorods. Effects of annealing temperature and reaction atmosphere on microstructure, phase, and magnetic property of Fe nanostructures were investigated. The as-obtained pure Fe nanoparticles with mean size of 45 nm had a high saturation magnetization up to 207 emu/g, close to that of bulk material (218 emu/g), which exhibited high air stability. After exposing in air for 2 and 7 days, the as synthesized Fe nanoparticles still showed high magnetization of 182 and 141 emu/g, respectively.

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    Nitrogen-doped graphene/carbon nanohorns composite as a high-performance supercapacitor electrode
    Lin Xiao-Qiang, Wang Wen-Dong, Lü Qiu-Feng, Jin Yan-Qiao, Lin Qilang, Liu Rui
    J. Mater. Sci. Technol., 2017, 33 (11): 1339-1345.  DOI: 10.1016/j.jmst.2017.06.006
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    Nitrogen-doped graphene/carbon nanohorns composite (NGLC) was prepared by one-step co-pyrolysis of graphene oxide, carbon nanohorns (CNHs), urea, and lignosulfonate. CNHs as spacers were inserted into graphene nanosheets. The introduction of CNHs and the loosened nano-structure of NGLC make it achieve a high specific capacitance of 363 F g-1 at a discharge current density of 1 A g-1, and NGLC exhibits an ultrahigh stability of 93.5% capacitance retention ratio after 5000 cycles. The outstanding comprehensive electrochemical performance of NGLC could meet the need of the future acted as an efficient supercapacitor electrode material.

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    Wear behavior of WC-Ni sliding against graphite under water lubrication
    Zhang Gaolong, Liu Ying, Wang Yuechang, Guo Fei, Liu Xiangfeng, Wang Yuming
    J. Mater. Sci. Technol., 2017, 33 (11): 1346-1352.  DOI: 10.1016/j.jmst.2017.01.006
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    Wear of hard materials in contact with softer materials is a neglected area of research. However, we observed considerable wear phenomenon at a hard WC-Ni surface sliding over soft graphite under water lubrication. The influences of applied load and the application history on the wear of surface were addressed in our experimental design. Wear of both graphite and WC-Ni surfaces increased with a greater applied load and repeated sliding. The topographies of the worn surfaces showed clear micro-scratches on the hard WC-Ni surface. Scanning electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the abrasive wear of the WC-Ni surface could be attributed to hard WC particles embedded in the graphite surface. These hard particles were formed by shearing of sharp WC-Ni asperities under certain conditions and intrinsic defects of the WC-Ni surface could accelerate this wear process.

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    Energy Absorption and Deformation Mechanism of Lotus-type Porous Coppers in Perpendicular Direction
    Li Weidong, Xu Kai, Li Honghao, Jia Haoling, Liu Xinhua, Xie Jianxin
    J. Mater. Sci. Technol., 2017, 33 (11): 1353-1361.  DOI: 10.1016/j.jmst.2017.01.009
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    As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s-1 to?~2400 s-1. The energy absorption capacity and the energy absorption efficiency are calculated to be 4-16 kJ/kg and 0.32-0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.

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    A systematic study of the antiferromagnetic-ferromagnetic conversion and competition in MnNiGe:Fe ribbon systems
    Zhang Lin, Ma Shengcan, Ge Qing, Liu Kai, Jiang Qingzheng, Han Xingqi, Yang Sheng, Yu Kun, Zhong Zhenchen
    J. Mater. Sci. Technol., 2017, 33 (11): 1362-1370.  DOI: 10.1016/j.jmst.2017.01.012
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    MnNiGe:Fe ribbon samples are prepared. Partial Ni- and Mn-substitution of Fe element can both induce the antiferromagnetic-ferromagnetic conversion in the TiNiSi-type state of these MnNiGe:Fe ribbon systems. It is found out, however, that some factors such as annealing, temperature variation process, field-cycling, substituted site and magnetic field can affect the conversion and competition between the antiferromagnetic and ferromagnetic states in these ribbons. Therefore, in this paper these major influencing factors are studied systematically and further discussed are the related magnetic and magnetocaloric properties in MnNiGe:Fe ribbon systems.

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    Shear anisotropy: Tuning high temperature metal hexaborides from soft to extremely hard
    Zhou Yanchun, Dai Fuzhi, Xiang Huimin, Liu Bin, Feng Zhihai
    J. Mater. Sci. Technol., 2017, 33 (11): 1371-1377.  DOI: 10.1016/j.jmst.2017.01.022
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    Easy machining into sharp lending edge, nose tip and complex shape components plays a pivotal role in the application of ultrahigh temperature ceramics in hypersonic vehicles, wherein low and controllable hardness is a necessary parameter to ensure the easy machinability. However, the mechanism that driving the hardness of metal hexaborides is not clear. Here, using a combination of the empirical hardness model for polycrystalline materials and density functional theory investigation, the hardness dependence on shear anisotropic factors of high temperature metal hexaborides has been established. It has come to light that through controlling the shear anisotropic factors the hardness of polycrystalline metal hexaborides can be tailored from soft and ductile to extremely hard and brittle, which is underpinned by the degree of chemical bonding anisotropy, i.e., the difference of B-B bond within the B6 octahedron and that connecting the B6 octahedra.

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    Effect of heat treatment on the microstructure and properties of CVD SiC fiber
    Zhao Chuanbao, Wang Yumin, Zhang Guoxing, Yang Qing, Zhang Xu, Yang Li_na, Yang Rui
    J. Mater. Sci. Technol., 2017, 33 (11): 1378-1385.  DOI: 10.1016/j.jmst.2017.02.009
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    In this study, the effect of heat treatment on the room temperature strength of W-core SiC fiber produced by chemical vapor deposition (CVD) was investigated. Thermal exposure in the temperature range of 900-1000 °C decreases the strength of the SiC fiber. Fracture morphology analysis indicates that failure initiations predominantly take place at the W-core/SiC interface. A reaction layer that formed at the W-core/SiC interface during thermal exposure degraded the fiber strength and an empirical linear relationship of strength vs thickness of the reaction layer can be obtained. The kinetics of the growth of the W-core/SiC reaction layer were determined.

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    Polycrystalline diamond compact with enhanced thermal stability
    Liu Shiqi, Han Lei, Zou Yongtao, Zhu Pinwen, Liu Baochang
    J. Mater. Sci. Technol., 2017, 33 (11): 1386-1391.  DOI: 10.1016/j.jmst.2017.03.014
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    Polycrystalline diamond compacts (PDC), which are composed of diamond and WC/Co substrate, and synthesized at high pressure and high temperature (HPHT), are widely applied as the tooth of drilling bit. However, the thermal stability of PDC will be reduced when diamond transforms into graphite due to cobalt in PDC acting as a catalyst during the drilling work. In this study, a new three-layer structured PDC with enhanced thermal stability has been successfully synthesized at pressures of 5.5-7.0 GPa and temperatures of 1650-1750 °C. In this structure, the diamond-SiC composite acts as the working layer, and the diamond-SiC-Co composite and WC/Co cements are as the intermediate layer and substrate, respectively. It is found that the initial oxidizing temperature of the three-layered PDC is enhanced up to 820 °C, which is significantly higher than that (~780 °C) of the conventional PDC counterpart.

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    Active metal brazing of SiO2-BN ceramic and Ti plate with Ag-Cu-Ti + BN composite filler
    Yang Z.W., Wang C.L., Wang Y., Zhang L.X., Wang D.P., Feng J.C.
    J. Mater. Sci. Technol., 2017, 33 (11): 1392-1401.  DOI: 10.1016/j.jmst.2017.04.005
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    SiO2-BN ceramic and Ti plate were joined by active brazing in vacuum with Ag-Cu-Ti + BN composite filler. The effect of BN content, brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated. The results showed that a continuous TiN-TiB2 reaction layer formed adjacent to the SiO2-BN ceramic, whose thickness played a key role in the bonding properties. Four Ti-Cu compound layers, Ti2Cu, Ti3Cu4, TiCu2 and TiCu4, were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag. The central part of the joint was composed of Ag matrix, over which some fine-grains distributed. The added BN particles reacted with Ti in the liquid filler to form fine TiB whiskers and TiN particles with low coefficients of thermal expansion (CTE), leading to the reduction of detrimental residual stress in the joint, and thus improving the joint strength. The maximum shear strength of 31 MPa was obtained when 3 wt% BN was added in the composite filler, which was 158% higher than that brazed with single Ag-Cu-Ti filler metal. The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content, brazing temperature and holding time. Based on the correlation between the microstructural evolution and brazing parameters, the bonding mechanism of SiO2-BN and Ti was discussed.

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    Spontaneous escape behavior of silver from graphite-like carbon coating and its inhibition mechanism
    Shao Wenting, Zhang Xinyu, Jiang Bailing, Liu Cancan, Li Hongtao
    J. Mater. Sci. Technol., 2017, 33 (11): 1402-1408.  DOI: 10.1016/j.jmst.2017.07.024
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    A series of silver-doped graphite-like carbon coatings was prepared on the surface of aluminum alloy using the magnetron sputtering method. The spontaneous escape behavior and inhibition mechanism of silver from graphite-like carbon coating were studied. The results showed that when the sample prepared with a 0.01-A current on the silver target was placed in an atmospheric environment for 0.5 h, an apparent silver escape phenomenon could be observed. However, the silver escape phenomenon was not observed for samples prepared with a 0.05-A current on the silver target if the sample was retained in a 10-1 Pa vacuum environment, even after 48 h. Compared with the sample placed in the atmospheric environment immediately after an ion plating process, the silver escape time lagged for 6 h. Nanometer-thick pure carbon coating coverage could effectively suppress silver escape. When the coating thickness reached 700 nm, permanent retention of silver could be achieved in the silver-doped graphite-like carbon coating. As the silver residue content in the graphite-like carbon coating increased from 2.27 at.% to 5.35 at.%, the interfacial contact resistance of the coating decreased from 51 mΩ cm2 to 6 mΩ cm2.

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    Effect of activators on the properties of nickel coated diamond composite powders
    Zuo Zongshi, Hu Bonian, Chen Hong, Dong Qizhi, Yu Gang
    J. Mater. Sci. Technol., 2017, 33 (11): 1409-1415.  DOI: 10.1016/j.jmst.2017.10.001
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    Nickel coated diamond composite powders were fabricated via a newly developed direct electrodeposition technique. The effects of activators on the coating of diamond were firstly investigated and diamond grinding wheels were then prepared from Ni-coated diamond composite powders with different activators. The microstructural characterizations of this composite powders were finally conducted by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, and the mechanical and tribological properties of as-prepared diamond grinding wheels were also measured. There are changes in microstructures and properties of the composite powders with activators. The activator concentration also has an influence on the morphologies and phase structures of the Ni coating on diamond particles. The composite powders with more compact coating of nickel can be prepared by adding 1 g dm-3 or more AgNO3 as an activator to electrodeposit nickel on diamond. The mechanical and tribological properties of diamond grinding wheels were significantly improved when the coating phase structure of Ni crystal grew with (111) plane orientation on the surface of diamond particles. The wheels made from nickel coated diamond composite powders possessed the advantages of easy preparation and outstanding tribological properties. Therefore, Ni coated diamond composite powders exhibit a great potential to be extensively applied in diamond cutting and grinding tools.

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    Comparative study of mechanical and wear behavior of Cu/WS2 composites fabricated by spark plasma sintering and hot pressing
    Wang Qunchang, Chen Minghui, Shan Zhongmao, Sui Chengguo, Zhang Lin, Zhu Shenglong, Wang Fuhui
    J. Mater. Sci. Technol., 2017, 33 (11): 1416-1423.  DOI: 10.1016/j.jmst.2017.06.014
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    The mechanical and wear behavior of copper-tungsten disulfide (Cu/WS2) composites fabricated by spark plasma sintering (SPS) and hot pressing (HP) was investigated, comparatively. Results indicated that the addition of lubricant WS2 substantially reduced wear rate of the Cu matrix composites fabricated by SPS, and the optimum content of WS2 is 20?wt% with regard to the wear behavior. However, it affected a little to the wear rate while dramatically decreased the friction coefficient of the composite fabricated by HP. This difference in friction behavior of the self-lubricating composites fabricated by the two techniques was closely related to their different mechanical properties. Severe interfacial reaction occurred during spark plasma sintering, leading to brittle phase formation at interface.

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    Thermal properties of polyurethane elastomer with different flexible molecular chain based on para-phenylene diisocyanate
    Lei Wanqing, Fang Changqing, Zhou Xing, Li Jiabin, Yang Rong, Zhang Zisen, Liu Donghong
    J. Mater. Sci. Technol., 2017, 33 (11): 1424-1432.  DOI: 10.1016/j.jmst.2017.05.014
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    This work focuses on the relationship between flexibility of molecular chains and thermal properties of polyurethane elastomer (PUE), which laid the foundation of further research about how to improve thermal properties of PUE. A series of PUE samples with different flexibility of molecular chains was prepared by using 1,4-butanediol (1,4-BDO)/bisphenol-a (BPA) blends with different mole ratios including 9/1, 8/2, 7/3, 6/4 and 5/5. As comparison, PUE extended with pure 1,4-BDO and BPA was also synthesized. These samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), etc. The results showed that with the decrease in flexibility of molecular chains the glass transition temperature (Tg) increased and low-temperature properties became worse. Besides, all samples had a certain degree of microphase separation, and soft segments in some samples were crystallized, i.e. the decreasing flexibility of molecular chains led to the impossibility of chains tightly packing and crystalline domains forming so that the degree of microphase separation decreased and the thermal properties became worse.

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