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CN 21-1315/TG
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      17 August 2018, Volume 34 Issue 8 Previous Issue    Next Issue
    Orginal Article
    A review of Fe3O4 thin films: Synthesis, modification and applications
    Wang Xiaoyi, Liao Yulong, Zhang Dainan, Wen Tianlong, Zhong Zhiyong
    J. Mater. Sci. Technol.. 2018, 34 (8): 1259-1272.   DOI: 10.1016/j.jmst.2018.01.011
    Abstract   HTML   PDF (5757KB)

    Magnetite (Fe3O4) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe3O4 thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe3O4 thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe3O4 thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe3O4 thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe3O4 thin films will give us some breakthroughs in materials science and technology.

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    Structural design of Cr/GLC films for high tribological performance in artificial seawater: Cr/GLC ratio and multilayer structure
    Li Lei, Guo Peng, Liu Lin-Lin, Li Xiaowei, Ke Peiling, Wang Aiying
    J. Mater. Sci. Technol.. 2018, 34 (8): 1273-1280.   DOI: 10.1016/j.jmst.2017.12.002
    Abstract   HTML   PDF (2996KB)

    In this paper, graphite-like carbon (GLC) films with Cr buffer layer were fabricated by DC magnetron sputtering technique with the thickness ratio of Cr to GLC films varying from 1:2 to 1:20. The effect of Cr/GLC modulation ratio on microstructure, mechanical and tribological properties in artificial seawater was mainly investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nano-indenter and a reciprocating sliding tribo-meter. The propagation of defects plays an important role in the evolution of delamination, which is critical to wear failure of GLC films in artificial seawater. Designing the proper multilayer structure could inhibit the defects propagation and thus protect the basis material. The multilayer Cr/GLC film with optimized ratio of 1:3 demonstrates a low average friction coefficient of 0.08?±?0.006 and wear rate of (2.3?±?0.3)?×?10-8?mm3/(N?m) in artificial seawater, respectively.

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    Microstructure and intergranular stress corrosion cracking susceptibility of a SA508-52M-316L dissimilar metal weld joint in primary water
    Dong Lijin, Peng Qunjia, Han En-Hou, Ke Wei, Wang Lei
    J. Mater. Sci. Technol.. 2018, 34 (8): 1281-1292.   DOI:
    Abstract   HTML   PDF (7804KB)

    Correlation of microstructure and intergranular stress corrosion cracking (IGSCC) susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain rate tension test following a microstructure characterization. The susceptibility to IGSCC in various regions of the dissimilar metal weld joint was observed to follow the order of Alloy 52 Mb> the heat affected zone of 316L> the dilution zone of Alloy 52 Mw> Alloy 52 Mw weld metal. The chromium-depletion at the grain boundary is the dominant factor causing the high IGSCC susceptibility of Alloy 52 Mb. However, IGSCC initiation in the heat affected zone of 316L is attributed to the increase of residual strain adjacent to the grain boundary. In addition, the decrease of chromium content and increase of residual strain adjacent to the grain boundary increase the IGSCC susceptibility of the dilution zone of Alloy 52 Mw.

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    Bimodal TBCs with low thermal conductivity deposited by a powder-suspension co-spray process
    Zhang Wei-Wei, Li Guang-Rong, Zhang Qiang, Yang Guan-Jun, Zhang Guo-Wang, Mu Hong-Min
    J. Mater. Sci. Technol.. 2018, 34 (8): 1293-1304.   DOI: 10.1016/j.jmst.2017.11.052
    Abstract   HTML   PDF (6716KB)

    Advanced thermal barrier coatings (TBCs) with better thermal barrier performance are required by both advanced gas turbine and air engine. In this work, novel bimodal TBCs with low thermal conductivity were deposited and characterized by a novel co-spray approach with both solid powder and suspension. Experimental and finite element analyses were used to optimize the process parameters to prepare the specific morphology nanostructure features. With a comprehensive understanding on the influence of spraying parameters on the morphology of nano-particles, homogeneous nano-particle heaps with a large aspect ratio were introduced to conventional layered coatings by plasma co-spraying with suspension and solid powder. Co-sprayed bimodal microstructure composite coatings resulted from both wet suspension droplets and molten particle droplets exhibited low thermal conductivity. The thermal conductivity of the composite coating was 1/5 lower than that of the counterpart coatings by conventional plasma spraying with solid powder. This study sheds light to the structural tailoring towards the advanced TBCs with low thermal conductivity.

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    Mechanism of improved electromigration reliability using Fe-Ni UBM in wafer level package
    Gao Li-Yin, Zhang Hao, Li Cai-Fu, Guo Jingdong, Liu Zhi-Quan
    J. Mater. Sci. Technol.. 2018, 34 (8): 1305-1314.   DOI: 10.1016/j.jmst.2017.11.046
    Abstract   HTML   PDF (2488KB)

    Fe-Ni films with compositions of 73 wt% of Ni and 45 wt% of Ni were used as under bump metallization (UBM) in wafer level chip scale package, and their reliability was evaluated through electromigration (EM) test compared with commercial Cu UBM. For Sn3.8Ag0.7Cu(SAC)/Cu solder joints, voids had initiated at Cu cathode after 300 h and typical failures of depletion of Cu cathode and cracks were detected after 1000 h EM. While the SAC/Fe-Ni solder joints kept at a perfect condition without any failures after 1000 h EM. Moreover, the characteristic lifetime calculated by Weibull analysis for Fe-73Ni UBM (2121 h), Fe-45Ni UBM (2340 h) were both over three folds to Cu UBM’s (698 h). The failure modes for Fe-Ni solder joints varied with the different growth behavior of intermetallic compounds (IMCs), which can all be classified as the crack at the cathodic interface between solder and outer IMC layer. The atomic fluxes concerned cathode dissolution and crack initiation were analyzed. When Fe-Ni UBM was added, cathode dissolution was suppressed due to the low diffusivity of IMCs and opposite transferring direction to electron flow of Fe atoms. The smaller EM flux within solder material led a smaller vacancy flux in Fe-Ni solder joints, which can explain the delay of solder voids and cracks as well as the much longer lifetime under EM.

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    Effects of scanning speed on microstructure in laser surface-melted single crystal superalloy and theoretical analysis
    Wang Guowei, Liang Jingjing, Yang Yanhong, Shi Yu, Zhou Yizhou, Jin Tao, Sun Xiaofeng
    J. Mater. Sci. Technol.. 2018, 34 (8): 1315-1324.   DOI: 10.1016/j.jmst.2017.11.027
    Abstract   HTML   PDF (3906KB)

    Scanning speed is a critical parameter for laser process, which can play a key role in the microstructure evolution of laser melting. In the laser melting of single crystal superalloy, the effects of scanning speed were investigated by experimental analysis and computational simulation. The laser was scanning along [71ˉ0] direction on (001) surface in different speeds. Solidification microstructures of dendrites growth direction and the primary dendritic spacing were analyzed by metallograph. Besides, a planar interface during solidification was taken into attention. Experiment results indicated that the primary dendritic spacing and thickness of planar interface decrease with the increase of speed. Through simulation, distribution of dendrites growth velocity and thermal gradient along dendrite growth direction were calculated, and the simulation of dendrites growth direction agreed with the experiment results. Additionally, a constant value was acquired which can be used to predict the primary dendritic spacing. Moreover, according to curve-fitting method and inequality relation, a model was proposed to predict the thickness of planar interface.

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    Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms
    Xu Dake, Zhou Enze, Zhao Ying, Li Huabing, Liu Zhiyong, Zhang Dawei, Yang Chunguang, Lin Hai, Li Xiaogang, Yang Ke
    J. Mater. Sci. Technol.. 2018, 34 (8): 1325-1336.   DOI: 10.1016/j.jmst.2017.11.025
    Abstract   HTML   PDF (4146KB)

    An antibacterial 2205-Cu duplex stainless steel (DSS) was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu2+ ions from the 2205-Cu DSS surface. In this work, the microbiologically influenced corrosion (MIC) resistance of 2205-Cu DSS in the presence of the corrosive marine bacterium Pseudomonas aeruginosa was investigated. The addition of copper improved the mechanical properties such as the yield strength, the tensile strength and the hardness of 2205 DSS. Electrochemical test results from linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and critical pitting temperature (CPT) measurements showed that 2205-Cu DSS possessed a larger polarization resistance (Rp), charge transfer resistance (Rct) and CPT values, indicating the excellent MIC resistance of 2205-Cu DSS against the corrosive P. aeruginosa biofilm. The live/dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS. The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14 d in the presence of P. aeruginosa (2.2 μm vs 12.5 μm). 2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P. aeruginosa.

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    High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La-Fe-Si plate produced by centrifugal casting
    Xu Zhishuai, Dai Yuting, Fang Yue, Luo Zhiping, Han Ke, Song Changjiang, Zhai Qijie, Zheng Hongxing
    J. Mater. Sci. Technol.. 2018, 34 (8): 1337-1343.   DOI: 10.1016/j.jmst.2017.11.023
    Abstract   HTML   PDF (3444KB)

    A sub-rapidly solidified LaFe11.6Si1.4 plate was fabricated directly from liquid by centrifugal casting method. The phase constitution, microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and physical property measurement system. When the plate was annealed at 1373 K, τ1 phase was formed by a solid-state peritectoid reaction. A first-order magnetic phase transition occurred in the vicinity of 188 K, and the effective refrigeration capacities reached 203.5 J/kg and 209.7 J/kg in plates annealed for 1 h and 3 h, respectively, under a magnetic field change of 3 T. It is suggested that centrifugal casting may become a new approach to prepare high-performance La-Fe-Si magnetocaloric plates for practical applications, which could largely accelerate the formation of τ1 phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.

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    Atom probe tomographic observation of hydrogen trapping at carbides/ferrite interfaces for a high strength steel
    Jiang Y.F., Zhang B., Zhou Y., Wang J.Q., Han E.-H., Ke W.
    J. Mater. Sci. Technol.. 2018, 34 (8): 1344-1348.   DOI: 10.1016/j.jmst.2017.11.008
    Abstract   HTML   PDF (1723KB)

    A three-dimensional atom probe (3DAP) technique has been used to characterize the hydrogen distribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on carbide/ferrite interfaces along the grain boundaries. Slow strain rate tensile (SSRT) testing shows that the AISI 4140 steel is highly sensitive to hydrogen embrittlement. The corresponding fractographic morphologies of hydrogen charged specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the hydrogen trapping sites present in the grain boundaries are responsible for the hydrogen-induced intergranular fracture of AISI 4140. The direct observation of hydrogen distribution contributes to a better understanding of the mechanism of hydrogen embrittlement.

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    Effect of residual dissolved oxygen on the corrosion behavior of low carbon steel in 0.1 M NaHCO3 solution
    Xue Fang, Wei Xin, Dong Junhua, Nabuk Etim Ini-Ibehe, Wang Changgang, Ke Wei
    J. Mater. Sci. Technol.. 2018, 34 (8): 1349-1358.   DOI: 10.1016/j.jmst.2017.11.004
    Abstract   HTML   PDF (2201KB)

    The effect of residual dissolved oxygen (DO) on the corrosion behavior of carbon steel in 0.1 M NaHCO3 solution was investigated by electrochemical measurements, corrosion mass loss test, scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the initial immersion stage, the increase of the dissolved oxygen concentration led to the change of from a reductive state of active dissolution to an oxidizing state of pseudo passivation in low carbon steel. While in the final stage, all the steels transformed into the steady state of pseudo passivation. In the anaerobic solution, the formation of α-FeOOH was attributed to the chemical oxidization of the ferrous corrosion products and the final cathodic process only included the reduction of α-FeOOH, while in the aerobic solution, it included the reduction of oxygen and α-FeOOH simultaneously. As the main corrosion products, the content of α-FeOOH was increased while that of Fe6(OH)12CO3 was decreased with increasing concentration of dissolved oxygen. The total corrosion mass loss of the steel was promoted with the increase of dissolved oxygen concentration.

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    An intrinsic correlation between driving force and energy barrier upon grain boundary migration
    Lin Bo, Wang Kang, Liu Feng, Zhou Yaohe
    J. Mater. Sci. Technol.. 2018, 34 (8): 1359-1363.   DOI: 10.1016/j.jmst.2017.11.002
    Abstract   HTML   PDF (1176KB)

    The migration of grain boundary (GB), which plays a key role in the microstructural evolution of polycrystalline materials, remains mysterious due to the unknown relationship between GB mobility associated with specific geometry and external conditions (e.g. temperature, stress, etc., hence the thermodynamic driving force). Combining the rate equation of GB migration with molecular dynamics simulations, an intrinsic correlation between driving force and energy barrier for the migration of various types of GBs (i.e. twist, symmetric tilt, asymmetric tilt, and mixed twist-tilt) is herein explored, showing the decrease of energy barrier with increasing thermodynamic driving force.

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    Orientation dependence of deformation twinning in Cu single crystals
    Cai S.S., X.W.Li, N.R.Tao
    J. Mater. Sci. Technol.. 2018, 34 (8): 1364-1370.   DOI: 10.1016/j.jmst.2017.10.004
    Abstract   HTML   PDF (2661KB)

    Cu single crystals were subjected to dynamic compression plastic deformation to investigate orientation-dependent twinning. The experimental results showed that twinning is closely related to the ratio of the maximum Schmid factor for twinning partial (mT) to the maximum Schmid factor for perfect dislocation (mS), i.e., mT/mS, rather than mT. The twin volume fraction VT increases with the mT/mS value and the most favorable orientation for twinning has the maximum mT/mS value (1.15). The relationships of mT/mS with both effective stacking fault energy γeff and threshold stress for twinning τT were established for understanding orientation-dependent twinning. Further insights into the orientation-dependent twinning and guidance for developing bulk high density nanotwinned materials are provided.

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    Polysaccharide-based magnetically responsive polyelectrolyte hydrogels for tissue engineering applications
    Madhusudana Rao Kummara, Kumar Anuj, Soo Han Sung
    J. Mater. Sci. Technol.. 2018, 34 (8): 1371-1377.   DOI: 10.1016/j.jmst.2017.10.003
    Abstract   HTML   PDF (2154KB)

    Polysaccharide-based bionanocomposite hydrogels with functional nanomaterials were used in biomedical applications. Self-organization of xanthan gum and chitosan in the presence of iron oxide magnetic nanoparticles (Fe3O4 MNPs) allowed us to form magnetically responsive polyelectrolyte complex hydrogels (MPECHs) via insitu ionic complexation using D-(+)-glucuronic acid δ-lactone as a green acidifying agent. Characterization confirmed the successful formation of (and structural interactions within) the MPECH and good porous structure. The rheological behavior and compressive properties of the PECH and MPECH were measured. The results indicated that the incorporation of Fe3O4 MNPs into the PECH greatly improved mechanical properties and storage modulus (G'). In vitro cell culture of NIH3T3 fibroblasts on MPECHs showed improvements in cell proliferation and adhesion in an external magnetic field relative to the pristine PECH. The results showed that the newly developed MPECH could potentially be used as a magnetically stimulated system in tissue engineering applications.

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    Design and preparation of gradient graphite/cermets self-lubricating composites
    Zhou, Xiong Ji, Guo Zhixing, Ye Junliu
    J. Mater. Sci. Technol.. 2018, 34 (8): 1378-1386.   DOI: 10.1016/j.jmst.2017.09.018
    Abstract   HTML   PDF (2899KB)

    Based on the functionally graded materials (FGMs) design concept, the laminated-graded graphite/cermets self-lubricating composite was prepared to achieve the integration of mechanical properties and lubrication performance of the cermet. The effects of the layer number and thickness of graded structure on residual stresses in the gradient composites were investigated by finite element method (FEM). From the FEM analyses, the optimal gradient structure design was obtained corresponding to the following parameters: the number of graded layers n = 2 and the thickness of graded structure t = 1 mm. According to the optimum design, a graded graphite/cermets self-lubricating material with two layers was fabricated by a typical powder metallurgy technique. Compared with the homogenous graphite/cermets composite, the surface hardness and indentation fracture toughness of graded composite were increased by approximately 15.9% and 6.3%, respectively. The results of X-ray diffraction (XRD) stress measurement identified the existence of residual compressive stress on the surface of graded composite. Additionally, the friction and wear tests revealed that the wear resistance of the graphite/cermets self-lubricating composite was improved significantly via the graded structural design, whereas the coefficient of friction changed slightly.

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    Formation process of akaganeite in the simulated wet-dry cycles atmospheric environment
    Xiao Haigang, Ye Wei, Song Xiaoping, Ma Yuantai, Li Ying
    J. Mater. Sci. Technol.. 2018, 34 (8): 1387-1396.   DOI: 10.1016/j.jmst.2017.06.020
    Abstract   HTML   PDF (4073KB)

    In order to clarify the formation mechanism and conditions for akaganeite in long-term exposure, the influence of the former corrosion results on akaganeite formation was investigated by simulated experiments in laboratory. The combination of XRD, FTIR, SEM and EPMA enabled the identification of the rust layer formed on the surface. Accordingly, the nature of the rust layer and the amount of the corrosive species in the rust layer varied with the extension of the exposure. Among them, comparing with the corrosion condition in initial stage, the structure of rust layer after repeated wet-dry cycles was disadvantage for akaganeite formation. Element Cl aggregated at the interface between rust and substrate in the thick part can participate in the formation of akaganeite after the rust layer covered removed. The accumulation effect of salt deposited contributed to akaganeite formation under the condition that salt deposition rate was relatively low.

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    In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering
    Lee Junho, Lee Dongju, Hoon Song Myung, Rhee Wonhyuk, Jin Ryu Ho, Hyung Hong Soon
    J. Mater. Sci. Technol.. 2018, 34 (8): 1397-1404.   DOI: 10.1016/j.jmst.2017.03.006
    Abstract   HTML   PDF (2818KB)

    Fe alloy composites reinforced with in-situ titanium carbide (TiC) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties of in-situ TiC/Fe alloy composites. The microstructure showed that the in-situ synthesized TiC particles were spherical with a size of 1-3 μm, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiCx at the common sintering temperature. The in-situ TiC/Fe alloy composite with C/Ti = 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon (C/Ti = 1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon (C/Ti = 0.8) caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC particles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.

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    Achieving the high phase purity of CH3NH3PbI3 film by two-step solution processable crystal engineering
    Li Yan, Ding Bin, Yang Guan-Jun, Li Chang-Jiu, LiState Cheng-Xin
    J. Mater. Sci. Technol.. 2018, 34 (8): 1405-1411.   DOI: 10.1016/j.jmst.2017.11.003
    Abstract   HTML   PDF (2674KB)

    To date, it is still a great challenge for highly efficient perovskite devices to realize the high quality perovskite films with high purity, high coverage ratio and good crystallization by two-step scalable solution method. In this study, a series PbI2 films with tunable micro-architecture of PbI2 crystals are prepared via solution processable crystal engineering. The perovskite film, prepared by optimized pit spacing in gas pumped PbI2 film at 1000?Pa, shows the highest film quality, including no residual PbI2 phase, compact morphology, and improved photoluminescence intensity. A transformation kinetics shows that the pit spacing strongly influences both the mass transfer and the sequential intercalation reaction between CH3NH3I and PbI2 crystals, which ultimately determines the full reaction state of the perovskite film. The perovskite solar cells assembled by the perovskite film show both high power-conversion efficiency and good reproducibility of photovoltaic performance due to the restrained charge recombination arising from the high quality perovskite film.

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    Cobalt(II) coordination polymers as anodes for lithium-ion batteries with enhanced capacity and cycling stability
    Luo Yumei, Sun Lixian, Xu Fen, Wei Siyue, Wang Qingyong, Peng Hongliang, Chen Chonglin
    J. Mater. Sci. Technol.. 2018, 34 (8): 1412-1418.   DOI: 10.1016/j.jmst.2017.11.006
    Abstract   HTML   PDF (2140KB)

    Coordination polymer Co-btca (H4btca=1,2,4,5-benzenetetracarboxylic acid) was synthesized using a simply hydrothermal method. In particular, the as-prepared Co-btca was applied as an anode material for lithium-ion battery for the first time. Single crystal X-ray diffraction results indicated that the as-prepared Co-btca displayed unique layer structure, which was beneficial to transport Li ions and electrons. Also, owing to the porous structure and appropriate specific surface area, Co-btca electrode delivered a reversible capacity of 801.3mA h/g after 50 cycles at a current density of 200mA/g. The reversible capacity of 773.9mA h/g was maintained after 200 cycles at a current density of 500 mA/g, exhibiting enhanced cycle stability. It also showed improved rate performance, making it a promising anode material and a new choice for lithium-ion batteries.

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    Effect of temperature on corrosion behavior of alloy 690 in high temperature hydrogenated water
    Wang Jiazhen, Wang Jianqiu, Ming Hongliang, Zhang Zhiming, Han En-Hou
    J. Mater. Sci. Technol.. 2018, 34 (8): 1419-1427.   DOI: 10.1016/j.jmst.2017.11.028
    Abstract   HTML   PDF (3997KB)

    The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves, electrochemical impedance spectra (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The corrosion rate of Alloy 690 reaches a local maximum at 250 °C. The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200-300 °C. A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.

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    Enhanced tensile properties of a reversion annealed 6.5Mn-TRIP alloy via tailoring initial microstructure and cold rolling reduction
    Cai Minghui, Huang Hongshou, Su Junhua, Ding Hua, D. Hodgson Peter
    J. Mater. Sci. Technol.. 2018, 34 (8): 1428-1435.   DOI: 10.1016/j.jmst.2017.12.008
    Abstract   HTML   PDF (3554KB)

    The feasibility of improving the overall performance of medium Mn steels was demonstrated via tailoring the initial microstructure and cold rolling reduction. The combined effects of cooling patterns after hot rolling (HR) and cold rolling (CR) reductions show: (1) as the cooling pattern varied from furnace cooling (FC) to oil quenching (OQ), the intercritically annealed microstructure was dramatically refined and the fraction of recrystallized ferrite dropped, regardless of CR reductions. This resulted in both high yield/ultimate tensile strengths (YS/UTS) but low total elongation to fracture (El); (2) as the CR reduction increased from 50% to 75%, the OQ-samples after annealing exhibited a more refined microstructure with relatively higher fractions of retained austenite and sub-structure, leading to higher YS and UTS but lower El; whereas the FC samples appeared to exhibit little difference in overall tensile properties in both cases. The differences in microstructural evolution with cooling patterns and CR reductions were explained by the calculated accumulated effective strain (εAES), which was considered to be related to degrees of recovery and recrystallization of the deformed martensite (α’). The optimal tensile properties of ~1?GPa YS and ~40?GPa·% UTS×El were achieved in the OQ-50%CR annealed samples at 650?°C for 1?h. This was quite beneficial to large-scale production of ultra-high strength steels, owing to its serious springback during heavy cold working.

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    Analysis of micro-tubular SOFC stability under ambient and operating temperatures
    Kong∗ Wei, Zhang Wenxuan, Huang Hongyan, Zhang Yukun, Wu Jie, Xu Yu
    J. Mater. Sci. Technol.. 2018, 34 (8): 1436-1440.   DOI: 10.1016/j.jmst.2017.12.009
    Abstract   HTML   PDF (1183KB)

    The stability of micro-tubular solid oxide fuel cell (MT-SOFC) is predicted at ambient and operating temperatures via simulation method. The results reveal that as long as the anode failure probability satisfies the failure criterion of 1E-6 at ambient temperature, the anode will retain its structural integrity at operating temperature. For the electrolyte or cathode, the stress strength ratio at operating temperature is significantly higher than that at ambient temperature. For an inappropriate component thickness, the cathode maybe fractures at operating temperature. In order to ensure the stability of MT-SOFC, the cathode thickness must be smaller than the maximum cathode thickness (tmax-cathode), which is derived from: tmax-cathode = 5.49 + 5.54 te

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    Cr5Si3B and Hf5Si3B: New MAB phases with anisotropic electrical, mechanical properties and damage tolerance
    Zhou Yanchun, Xiang Huimin, Dai Fu-Zhi, Feng Zhihai
    J. Mater. Sci. Technol.. 2018, 34 (8): 1441-1448.   DOI: 10.1016/j.jmst.2017.12.014
    Abstract   HTML   PDF (3389KB)

    Through a combination of electronic structure, chemical bonding and mechanical property investigations, anisotropic electrical and mechanical properties, and damage tolerant ability of MAB phases Cr5Si3B and Hf5Si3B are predicted. The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in Cr5Si3B and Hf in Hf5Si3B, which mainly contribute to the electrical conductivity. The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of Cr5Si3B and Hf5Si3B. The high stiffness is determined by the strong covalent-ionic Cr1-B-Cr1 and Cr1-Si bonds in Cr5Si3B and the ionic-covalent Hf1-B-Hf1 and Si-B bonds in Hf5Si3B; while the low shear deformation resistance is attributed to the presence of metallic Cr-Cr, Hf-Hf and Si-Si bond. Based on the low Pugh’s ratio, Cr5Si3B and Hf5Si3B are predicted tolerant to damage. The possible cleavage plane is (0001) and the possible slip systems are <1 $\bar{1}$00>|{11 2ˉ0} and <11 $\bar{2}$0>|{0001} for both Cr5Si3B and Hf5Si3B.

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    Diffusion behavior at void tip and its contributions to void shrinkage during solid-state bonding
    Zhang C., Li M.Q., Li H.
    J. Mater. Sci. Technol.. 2018, 34 (8): 1449-1454.   DOI: 10.1016/j.jmst.2017.12.001
    Abstract   HTML   PDF (1740KB)

    Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface characteristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.

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