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ISSN 1005-0302
CN 21-1315/TG
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      20 September 2019, Volume 35 Issue 9 Previous Issue   
    Orginal Article
    Selective removal of heavy metal ions in aqueous solutions by sulfide-selector intercalated layered double hydroxide adsorbent
    Jing Wang, Liang Zhang, Tianshu Zhang, Ting Du, Tao Li, Tianli Yue, Zhonghong Li, Jianlong Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 1809-1816.   DOI: 10.1016/j.jmst.2019.04.016

    Remaining largely under-appreciated, a majority of metal ion sorbents are limited in their target selectivity. In this work, a 3D sulfide intercalated NiFe-layered double hydroxide (NFL-S) hierarchical sorbent has been synthesized for selective heavy metal removal. The intercalation of sulfurated groups in the interlayer of the layered double hydroxide (LDH) nanosheets endows NFL-S as a selective heavy metal ion filter; the selectivity of NFL-S for heavy metals is in the order of Pb2+ > Cu2+ ≥ Zn2+ > Cd2+> Mn2+, and NFL-S has high kd values for Pb2+ ($\widetilde{1}$06 mL/g) and Cu2+ ($\widetilde{1}$05 mL/g). Scanning electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffraction were used to analyze the composition of the as-prepared nanoadsorbent. The selective adsorption behavior was systematically studied using batch experiments, and the performance was evaluated through kinetic and isotherm studies. Moreover, the adsorption mechanism of heavy metals by NFL-S through surface complexation was also investigated, which shows great potential for water decontamination.

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    Weldability, microstructure and mechanical properties of laser-welded selective laser melted 304 stainless steel joints
    Jingjing Yang, Yun Wang, Fangzhi Li, Wenpu Huang, Guanyi Jing, Zemin Wang, Xiaoyan Zeng
    J. Mater. Sci. Technol.. 2019, 35 (9): 1817-1824.   DOI: 10.1016/j.jmst.2019.04.017

    Laser welding is a promising process for joining small components produced by selective laser melting (SLM) to fabricate the large-scale and complex-shaped parts. In the work, the morphology, microstructure, microhardness, tensile properties and corrosion resistance of the laser welded stress-relieved SLMed 304 stainless steel joints are investigated, as the different sections of stress-relieved SLMed 304 stainless steel are joined. Results show that the SLMed 304 stainless steel plates have a good laser weldability. The microstructure of laser-welded joints consists of the cellular dendrites in austenite matrix within columnar grains, exhibiting a coarser dendrite structure, lower microhardness ($\widetilde{2}$20 HV) and tensile properties (tensile strength of $\widetilde{7}$50 MPa, and area reduction of $\widetilde{2}$7.6%), but superior corrosion resistance to those of SLMed plates. The dendrite arm spacing of the joints varies from $\widetilde{3}$.7 μm in center zone, to $\widetilde{5}$.0 μm in fusion zone, to $\widetilde{2}$.5 μm in epitaxial zone. The SLMed anisotropy shows a negligible effect on the microstructure and performance of the laser-welded joints. The laser welding along the building directions of the SLMed base plates can induce a slightly finer dendritic structure and higher tensile properties.

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    Thermally stable microstructures and mechanical properties of B4C-Al composite with in-situ formed Mg(Al)B2
    Yangtao Zhou, Yuning Zan, Shijian Zheng, Xiaohong Shao, Qianqian Jin, Bo Zhang, Quanzhao Wang, Bolv Xiao, Xiuliang Ma, Zongyi Ma
    J. Mater. Sci. Technol.. 2019, 35 (9): 1825-1830.   DOI: 10.1016/j.jmst.2019.04.019

    B4C particulate-reinforced 6061Al composite was fabricated by powder metallurgy method. The as-rolled composite possesses high tensile strength which is comparable to that of the peak-aged 6061Al alloy. More importantly, the microstructures and mechanical properties are thermally stable during long-term holding at elevated temperature (400 °C). The microstructual contributions to the strength of the composite were discussed. Transmission electron microscopy (TEM) analysis indicates that the in-situ formed reinforcement Mg(Al)B2, as products of the interfacial reactions between B4C and the aluminum matrix, show not only good resistance to thermal coarsening but also strong pinning effect to the grain boundaries in the alloy matrix.

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    Corrosion behavior of copper T2 and brass H62 in simulated Nansha marine atmosphere
    Xiao Lu, Yuwei Liu, Miaoran Liu, Zhenyao Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 1831-1839.   DOI: 10.1016/j.jmst.2019.04.024

    The accelerated corrosion behavior of copper T2 and brass H62 exposed in simulated Nansha marine atmosphere for different periods were investigated by weight loss method, SEM, XRD and potentiodynamic polarization measurements. The results indicate that copper T2 and brass H62 underwent severe corrosion, and the final corrosion rates at 32 days of exposure were 0.24μm/d and 0.10μm/d, respectively. Moreover, the overall corrosion type of copper T2 was uniform and the corrosion products Cu2O and Cu2Cl(OH)3 played a vital role in the corrosion rate of copper. While the dezincification corrosion with zinc preferential dissolution was obvious in brass H62. The predominant phases were the zinc-rich compounds Zn5(OH)8Cl2·H2O, Zn12(SO4)3Cl3(OH)15·5H2O and NaZn4(SO4)Cl(OH)6·6H2O. There existed a large number of copper-rich holes with 20-50μm depth beneath the corrosion product layer.

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    Hierarchically 3D structured milled lamellar MoS2/nano-silicon@carbon hybrid with medium capacity and long cycling sustainability as anodes for lithium-ion batteries
    Peng Zhang, Qiang Ru, Honglin Yan, Xianhua Hou, Fuming Chen, Shejun Hu, Lingzhi Zhao
    J. Mater. Sci. Technol.. 2019, 35 (9): 1840-1850.   DOI: 10.1016/j.jmst.2019.05.002

    A hierarchically 3D structured milled lamellar MoS2/nano-silicon@carbon hybrid with medium capacity and long-term lifespan is designed by a green and scalable approach using ball milling process and spray-drying/pyrolysis routes. The microspheres consist of low-content nano-silicon (20 wt%), milled lamellar MoS2 sheets and porous carbon skeletons. A mixture of silicon nanoparticles and MoS2 flakes serves as an inner core, while porous carbon pyrolyzed from petroleum pitch acts as a protective shell. The particular architecture affords robust mechanical support, abundant buffering space and enhanced electrical conductivity, thus effectively accommodating drastic volume variation during repetitive Li+ intercalation/extraction. The Si/MoS2@C hybrid delivers a high initial discharge specific capacity of 1257.8 mA h g-1 and exhibits a reversible capacity of 767.52 mA h g-1 at a current density 100 mA g-1 after 250 cycles. Most impressively, the electrode depicts a superior long-cycling durability with a discharge capacity of 537.6 mA h g-1 even after 1200 cycles at a current density of 500 mA g-1. Meanwhile, the hybrid also shows excellent rate performance such as 388.1 mA h g-1 even at a large current density of 3000 mA g-1.

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    Dynamic recrystallization behavior of GH4169G alloy during hot compressive deformation
    Dan Jia, Wenru Sun, Dongsheng Xu, Fang Liu
    J. Mater. Sci. Technol.. 2019, 35 (9): 1851-1859.   DOI: 10.1016/j.jmst.2019.04.018

    The microstructure evolutions and nucleation mechanisms of GH4169 G alloy were studied by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The hot compression tests were performed different imposed reductions in the range of true strain from 0.12 to 1.2 at the temperatures of 930 ℃-1050 ℃ with strain rates of 0.01 s-1-1 s-1. It is found that cumulative and local misorientation increase firstly and then decrease when the strain is increased due to the progress of dynamic recrystallization (DRX). The low angle boundaries (LAGBs) rapidly develop to high angle boundaries (HAGBs) at relatively high deformation temperature or the low strain rate. There are three DRX mechanisms observed for GH4169 G alloy during hot deformation. Discontinuous dynamic recrystallization (DDRX) as the dominant mechanism for GH4169 G alloy is characterized by typical necklace structures and bulged-original boundaries. Besides, different deformation bands with dislocation cells formed in deformed matrix at low temperature and large strain, which indicates that continuous dynamic recrystallization (CDRX) contributed to the DRX process. The twin boundaries lost their coherent characteristics and provide sites for nucleation, which also accelerates the nucleation of DRX.

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    Enhanced tensile properties in a Mg-6Gd-3Y-0.5Zr alloy due to hot isostatic pressing (HIP)
    B. Zhou, D. Wu, R.S. Chen, En-hou Han
    J. Mater. Sci. Technol.. 2019, 35 (9): 1860-1868.   DOI: 10.1016/j.jmst.2019.05.006

    Hot isostatic pressing (HIP) was applied to Mg-6Gd-3Y-0.5Zr (GW63) alloy to reduce shrinkage porosity, thus, to enhance the integrity and reliability of castings. During HIP process, shrinkage porosity was closed by grain compatible deformation and subsequent diffusion across the bonding interface. The amount of initial shrinkage porosity was the key factor for shrinkage porosity closure. HIP was testified to be effective on shrinkage porosity reduction in GW63 alloy due to its relatively narrow solidification range and resultant low content of initial shrinkage porosity in most sections, leading to higher tensile properties both in as-cast and cast-T6 condition. The improvement in tensile properties was mainly because of shrinkage porosity reduction and resultant effective rare-earth (RE) elements homogenization and precipitation strengthening.

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    Micromechanical behavior of a fine-grained China low activation martensitic (CLAM) steel
    Wenyin Xue, Jinhua Zhou, Yongfeng Shen, Weina Zhang, Zhenyu Liu
    J. Mater. Sci. Technol.. 2019, 35 (9): 1869-1876.   DOI: doi.org/10.1016/j.jmst.2019.05.005

    Micromechanical behavior of a fine-grained China Low Activation Martensitic (CLAM) steel under nanoindentation was studied in this work. The grain size of the as-prepared 0.1Ti-CLAM steel is $\widetilde{5}$ μm and the average diameter of the spherical precipitates is $\widetilde{5}$ nm. Both elastic modulus and hardness decrease with increasing contact depth of the nanoindenter, following an exponential decreasing function. The abnormally large contact depths should be resulted from defect concentration under the indenter. The effect of nanosized precipitates on hardness is responsible for the pop-ins occurring in the load-depth curves, corresponding to the blockage of nanosized precipitates to the dislocation movement. Nanosized VC and M23C6precipitates with the volume fractions of 0.32% and 1.21% can be identified, respectively. Different strengthening mechanisms originated from the two types of nanosized precipitates. The blockage of dislocations by VC particles leads to an Orowan strengthening whilst dislocations could cut through theM23C6particles because of the large size of the particles. The strengthening effects originated from the VC and M23C6 precipitates lead to the strength increase of $\widetilde{4}$48 MPa and $\widetilde{2}$54 MPa, respectively.

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    Improving the hard magnetic properties by intragrain pinning for Ta doped nanocrystalline Ce-Fe-B alloys
    J.S. Zhang, W. Li, X.F. Liao, H.Y. Yu, L.Z. Zhao, H.X. Zeng, D.R. Peng, Z.W. Liu
    J. Mater. Sci. Technol.. 2019, 35 (9): 1877-1885.   DOI: 10.1016/j.jmst.2019.05.007

    To develop Ce based permanent magnets with high performance/cost ratio, Ta doping is was employed to enhance the magnetic performance of Ce-Fe-B alloys. For melt spun Ce17Fe78-xTaxB6 (x = 0-1) alloys, the coercivity Hc increases from 439 to 553 kA/m with increasing x value from 0 to 0.75. Microstructure characterizations indicate that Ta doping is helpful for grain refinement. A second phase of TaB2 is observed in Ce17Fe77.25Ta0.75B6 alloy, which acts as the pinning center of the magnetic domains, resulting in the change of coercivity mechanism from nucleation type to nucleation + pinning type. The micromagnetic simulation confirms that non-magnetic particles within hard magnetic phase can increase the demagnetization field around them and it is crucial for preventing the further magnetization reverse by pinning effect. Take the advantage of Ta doping for enhancing the coercivity, Ce content of Ce-Fe-B alloy can be further cut down to increase the remanence Jr due to the reduced volume fraction of CeFe2 phase and increased Fe/Ce ratio. As a result, a good combination of magnetic properties with Hc = 514 kA/m, Jr = 0.49 T, and the maximum energy product (BH)max = 36 kJ/m3 have been obtained in Ce15Fe79.25Ta0.75B6 alloy. It is expected that the present work can serve as a useful reference for designing new permanent magnetic materials with low-cost.

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    Effect of corrosive media on galvanic corrosion of complicated tri-metallic couples of 2024 Al alloy/Q235 mild steel/304 stainless steel
    Linjun Shi, Xiuying Yang, Yingwei Song, Dan Liu, Kaihui Dong, Dayong Shan, En-Hou Han
    J. Mater. Sci. Technol.. 2019, 35 (9): 1886-1893.   DOI: 10.1016/j.jmst.2019.04.022

    Galvanic corrosion of tri-metallic couples is more complicated than that of bi-metallic couples. In this study, the effect of the pH of corrosive media on the galvanic corrosion of 2024 Al alloy/Q235 mild steel/304 stainless steel tri-metallic couples was investigated using potentiodynamic polarization, scanning electron microscopy, scanning vibrating electrode technique and a multi-channel galvanic corrosion meter. The results show that 2024 always acts as the only anode in 3.5 wt% NaCl at pH 5.56, 9.72 and 12.0, while both Q235 and 2024 act as anodes at pH 2.39 in the initial stage and then the role of Q235 changes at longer coupling time, which can be attributed to the effect of pH on the surface film of 2024. It is also found that the galvanic current density of a tri-metallic couple is the superposition of two bi-metallic couples when cathodic reactions are controlled by the diffusion of oxygen, otherwise it is smaller than that of the sum of two bi-metallic couples. The localized corrosion instead of uniform corrosion of anodic metal is accelerated by galvanic corrosion.

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    Carboxymethyl chitosan as a polyampholyte mediating intrafibrillar mineralization of collagen via collagen/ACP self-assembly
    Mingli Lin, Huanhuan Liu, Jingjing Deng, Ran An, Minjuan Shen, Yanqiu Li, Xu Zhang
    J. Mater. Sci. Technol.. 2019, 35 (9): 1894-1905.   DOI: 10.1016/j.jmst.2019.05.010

    The significant role of the polyelectrolytic nature of non-collagenous proteins (NCPs) in regulating the in vivo mineralization of collagen provides important insights for scientists searching for analogues of NCPs to achieve in vitro collagen mineralization. Polyampholyte carboxymethyl chitosan (CMC) has both carboxyl and amino groups, which allows it to act as a cationic or anionic polyelectrolyte below or above its isoelectric point (IP), respectively. In this study, CMC was employed as the analogue of NCPs to stabilize amorphous calcium phosphate (ACP) under acidic conditions (pH < 3.5) via the formation of CMC/ACP nanocomplexes. In the presence of both ACP nanoparticles and acid collagen molecules, ACP nanoparticles could be integrated into collagen fibrils during the process of collagen self-assembly and achieve intrafibrillar mineralization of collagen in vitro (i.e., synchronous self-assembly/mineralization (SSM) of collagen). This mode of mineralization is different from established mechanisms in which mineralization follows the self-assembly (MFS) of collagen. Thus, SSM provides a new strategy for developing materials from mineralized collagen scaffolds.

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    Skin layer of A380 aluminium alloy die castings and its blistering during solution treatment
    Zihao Yuan, Zhipeng Guo, S.M. Xiong
    J. Mater. Sci. Technol.. 2019, 35 (9): 1906-1916.   DOI: 10.1016/j.jmst.2019.05.011

    Skin layer is a characteristic microstructure of aluminium die castings, which would effect the surface blistering during solution treatment. In this study, the microstructures of skin layer were investigated by the methods of optical microscope (OM), scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). High resolution X-ray CT was used to compare the skin layer with normal surface before and after solution treatment. With the aid of computational fluid dynamics (CFD), the formation mechanism of the skin layer was discussed based on microstructure distribution, solute segregation, porosity distribution and surface blistering. The results suggested that the skin layer is related to a succession of complex processes before the filling process finished. Pore clusters or laminar defects would be formed in skin layers during solution treatment and cause severe surface blistering.

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    Influences of Re on low-cycle fatigue behaviors of single crystal superalloys at intermediate temperature
    Liu Liu, Jie Meng, Jinlai Liu, Mingke Zou, Haifeng Zhang, Xudong Sun, Yizhou Zhou
    J. Mater. Sci. Technol.. 2019, 35 (9): 1917-1924.   DOI: 10.1016/j.jmst.2019.05.026

    Low-cycle fatigue behaviors of Ni-base single crystal superalloys containing different Re contents have been investigated at 760 °C. During heat treatment, Re retards γ′ phases coarsening and equalizes the distribution of γ′ phases. As Re content increases, fatigue life increases and slip bands distribute more inhomogeneously. Moreover, adding Re not only reduces stacking fault energy of the matrix, but also promotes the element segregation to increase the lattice misfit. However, the larger lattice misfit does not lead to the formation of dislocation networks, but which activates dislocation movement and promotes dislocations cross-slip and climbing movement under high temperature and applied stress. On the other hand, with the addition of Re, cyclic deformation behaviors change from cyclic hardening to cyclic stability, mainly depending on a transformation of deformation mechanisms from slip bands cutting through γ and γ′ phases to stacking faults shearing.

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    Controllable in-situ aging during selective laser melting: Stepwise precipitation of multiple strengthening phases in Inconel 718 alloy
    Huihui Yang, Jingjing Yang, Wenpu Huang, Guanyi Jing, Zemin Wang, Xiaoyan Zeng
    J. Mater. Sci. Technol.. 2019, 35 (9): 1925-1930.   DOI: 10.1016/j.jmst.2019.05.024
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    Synthesis and characterization of MoS2/Fe@Fe3O4 nanocomposites exhibiting enhanced microwave absorption performance at normal and oblique incidences
    Peng Wang, Junming Zhang, Guowu Wang, Benfang Duan, Donglin He, Tao Wang, Fashen Li
    J. Mater. Sci. Technol.. 2019, 35 (9): 1931-1939.   DOI: 10.1016/j.jmst.2019.05.021

    Herein, we attempted to prepare MoS2/Fe@Fe3O4 nanocomposites capable of strongly absorbing broadband incident electromagnetic (EM) radiation and probed the effects of their composition on complex permittivity and permeability at 2-18 GHz. Calculations of normal-incidence reflection losses (RLs) based on EM parameters revealed that the Fe@Fe3O4 to MoS2 mass ratio strongly influenced the absorption peak intensity and bandwidth. Specifically, an RL peak of -31.8 dB@15.3 GHz and a bandwidth (RL < - 10 dB) of 4.8 GHz (13.2-18 GHz) were achieved at a thickness of 1.52 mm and a Fe@Fe3O4 to MoS2 mass ratio of 60:40. Further, RL and bandwidth were investigated for oblique incidence, in which case two kinds of EM waves (TE - electric field perpendicular to plane of incidence; TM - electric field in the plane of incidence) were considered. The absorption peaks of TE and TM waves did not exceed -20 dB when the incidence angle increased to 30°, and the bandwidth (RL < - 10 dB) reached 4.2 GHz (TE wave) and 4.0 GHz (TM wave) when this angle was further increased to 40.0° and 50.4°, respectively. Finally, the mechanism of microwave absorption was discussed in detail.

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    Microstructure evolution of in-situ nanoparticles and its comprehensive effect on high strength steel
    Rongjian Shi, Zidong Wang, Lijie Qiao, Xiaolu Pang
    J. Mater. Sci. Technol.. 2019, 35 (9): 1940-1950.   DOI: 10.1016/j.jmst.2019.05.009

    A novel steel strengthened by nanoparticles was investigated in this study. A Fe-based high-strength steel was developed by the trace-element regional supply method during deoxidization to generate in situ nanoparticles with a high number density in the matrix. The results show that the endogenous nanoparticles are aluminum oxide (Al2O3) and titanium oxide (Ti3O5) formed in the liquid melt. Al2O3 functioned as a heterogeneous nucleation site for MnS during solidification; the size of the resultant complex inclusions was approximately 1-2 μm. Furthermore, 13 nm Nb(C,N) precipitates grew with the Ti3O5 during the tempering process. These in situ nanoparticles strongly affected refining of the grain and inclusions. The investigated steel was strengthened more than 200 MPa by precipitation strengthening and more than 265 MPa by grain refinement strengthening according to the Ashby-Orowan mechanism and the Hall-Petch relationship, respectively.

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    Phosphomolybdic acid-modified highly organized TiO2 nanotube arrays with rapid photochromic performance
    Yuanyuan Wei, Bing Han, Zhaojun Dong, Wei Feng
    J. Mater. Sci. Technol.. 2019, 35 (9): 1951-1958.   DOI: 10.1016/j.jmst.2019.05.014

    TiO2 nanotube arrays were prepared by means of an electrochemical anodization technique in an organic electrolyte solution doped with polyvinyl pyrrolidone (PVP) and were subsequently modified with phosphomolybdic acid (PMoA) to obtain PMoA/TiO2 nanotube arrays. The microstructure and photochromic properties were investigated via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), and X-ray photoelectron spectroscopy (XPS). The results indicated that the Keggin structure of PMoA and the nanotube structure of TiO2 were not destroyed, and there was a strong degree of interaction between PMoA and TiO2 at the biphasic interface with lattice interlacing during the compositing process. The XPS results further indicated that there was a change in the chemical microenvironment during the formation process of the composite, and a new charge transfer bridge was formed through the Mo-O-Ti bond. Under visible light irradiation, the colorless PMoA/TiO2 nanotube array quickly turned blue and exhibited a photochromic response together with reversible photochromism in the presence of H2O2. After visible light irradiation for 60 s, the appearance of Mo5+ species in the XPS spectra indicated a photoreduction process in accordance with a photoinduced electron transfer mechanism.

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    Bioactive glass nanotube scaffold with well-ordered mesoporous structure for improved bioactivity and controlled drug delivery
    Jian Xiao, Yizao Wan, Zhiwei Yang, Yuan Huang, Fanglian Yao, Honglin Luo
    J. Mater. Sci. Technol.. 2019, 35 (9): 1959-1965.   DOI: 10.1016/j.jmst.2019.04.027

    In this study, a novel mesoporous bioactive glass nanotube (MBGN) scaffold has been fabricated via template-assisted sol-gel method using bacterial cellulose (BC) as template and nonionic block copolymer (P123) as pore-directing agent. The scaffold was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and N2 adsorption-desorption analysis. Furthermore, simvastatin was used to evaluate the loading efficiency and release kinetics of the scaffold. The obtained scaffold displays nanofiber-like morphology, ordered mesopores on the tube walls, and interconnected three-dimensional (3D) network structure that completely replicates the BC template. In addition, it shows dual pore sizes (16.2 and 3.3 nm), large specific surface area (537.2 m2 g-1) and pore volume (1.429 cm3 g-1). More importantly, the scaffold possesses excellent apatite-forming ability and sustainable drug release as compared to the counterpart scaffold without mesopores. This unique scaffold can be considered a promising candidate for drug delivery and bone tissue regeneration.

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    Synthesis and microstructure characterization of tetragonal Zr1-xTixO2 (x = 0-1) solid solutions
    Linggen Kong, Inna Karatchevtseva, Hanliang Zhu, Meng Jun Qin, Zaynab Aly
    J. Mater. Sci. Technol.. 2019, 35 (9): 1966-1976.   DOI: 10.1016/j.jmst.2019.04.013

    Oxide powders of Zr1-xTixO2 (x = 0-1) solid solutions with micron-sized particles were synthesized via a solution combustion method. The synthesis process and Zr/Ti molar ratio were optimized to produce powders with the tetragonal crystal structure. X-ray diffraction, Raman spectroscopy and transmission electron spectroscopy results confirm that a full crystallization microstructure with the single tetragonal phase is obtained after calcination at 600 °C while maintaining the crystallite size <30 nm. Zr/Ti oxide mixtures with Zr ≥ 67 mol% exhibit a tetragonal crystal structure and the embedding Ti in ZrO2 improves the structure stability. The nitrogen sorption results indicate that the powders possess mesoporous morphology with medium specific surface areas ($\widetilde{1}$0-50 m2/g). Chemical stability tests show that these powders are relatively stable with negligible removal of titanium and zirconium after elution by 0.5 mol/L HCl. Density functional theory was used to calculate the most stable structure with low energy for the selected composition.

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    Facile synthesis of rutile TiO2/carbon nanosheet composite from MAX phase for lithium storage
    Zhaoruxin Guan, Xiaoxue Wang, Tingting Li, Qizhen Zhu, Mengqiu Jia, Bin Xu
    J. Mater. Sci. Technol.. 2019, 35 (9): 1977-1981.   DOI: 10.1016/j.jmst.2019.04.021

    Titanium oxide (TiO2), with excellent cycling stability and low volume expansion, is a promising anode material for lithium-ion battery (LIB), which suffers from low electrical conductivity and poor rate capability. Combining nano-sized TiO2 with conductive materials is proved an efficient method to improve its electrochemical properties. Here, rutile TiO2/carbon nanosheet was obtained by calcinating MAX (Ti3AlC2) and Na2CO3 together and water-bathing with HCl. The lamellar carbon atoms in MAX are converted to 2D carbon nanosheets with urchin-like rutile TiO2 anchored on. The unique architecture can offer plentiful active sites, shorten the ion diffusion distance and improve the conductivity. The composite exhibits a high reversible capacity of 247 mA h g-1, excellent rate performance (38 mA h g-1 at 50 C) and stable cycling performance (0.014% decay per cycle during 2000 cycles) for lithium storage.

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    Microstructure evolution and crystallography of directionally solidified Al2O3/Y3Al5O12 eutectic ceramics prepared by the modified Bridgman method
    Xu Wang, Nan Zhang, Yujie Zhong, Bailing Jiang, Langhong Lou, Jian Zhang, Jingyang Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 1982-1988.   DOI: 10.1016/j.jmst.2019.05.018Get rights and content

    Large size, high-density (99.97%) and well-organized Al2O3/Y3Al5O12 (YAG) eutectic ceramics were prepared by the modified Bridgman method. The evolution of the three dimensional microstructure and micropores were investigated. The diameter of the micro-pores and the porosity decreased during directional solidification. The average equivalent diameter of the micro-pores was 2.41 μm in the well-prepared eutectic ceramics. Most of the pores (98.07%) were smaller than 4 μm. These data are comparable to those prepared by the optical floating zone method. The as-grown eutectic ceramics were polycrystalline, but the interfaces were well-bonded and there were no amorphous phases in the microstructure. The misfits of the different crystallographic relationships were calculated, and the bottleneck of the single-crystal preparation was identified. These results could provide theoretical guidance for the preparation of large, single-crystal Al2O3/YAG eutectic ceramics by the modified Bridgman method.

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    Preparation of highly conductive graphene-coated glass fibers by sol-gel and dip-coating method
    Minghe Fang, Xuhai Xiong, Yabin Hao, Tengxin Zhang, Han Wang, Hui-Ming Cheng, You Zeng
    J. Mater. Sci. Technol.. 2019, 35 (9): 1989-1995.   DOI: 10.1016/j.jmst.2019.05.027

    In order to fabricate highly-conductive glass fibers using graphene as multi-functional coatings, we reported the preparation of graphene-coated glass fibers with high electrical conductivity through sol-gel and dip-coating technique in a simple way. Graphene oxide (GO) was partially reduced to graphene hydrosol, and then glass fibers were dipped and coated with the reduced GO (rGO). After repeated sol-gel and dip-coating treatment, the glass fibers were fully covered with rGO coatings, and consequently exhibited increased hydrophobicity and high electrical conductivity. The graphene-coated fibers exhibited good electrical conductivity of 24.9 S/cm, being higher than that of other nanocarbon-coated fibers and commercial carbon fibers, which is mainly attributed to the high intrinsic electrical conductivity of rGO and full coverage of fiber surfaces. The wettability and electrical conductivity of the coated fibers strongly depended on the dip-coating times and coating thickness, which is closely associated with coverage degree and compact structure of the graphene coatings. By virtue of high conductivity and easy operation, the graphene-coated glass fibers have great potential to be used as flexible conductive wires, highly-sensitive sensors, and multi-functional fibers in many fields.

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    Defective graphene as a high-efficiency Raman enhancement substrate
    Tong Zhao, Zhibo Liu, Xing Xin, Hui-Ming Cheng, Wencai Ren
    J. Mater. Sci. Technol.. 2019, 35 (9): 1996-2002.   DOI: 10.1016/j.jmst.2019.05.012

    Pristine graphene (PG) has been demonstrated to be an excellent substrate for Raman enhancement, which is called graphene-enhanced Raman scattering. However, the chemically inert and hydrophobic surface of PG hinders the adsorption of molecules especially in aqueous solutions, and consequently limits the Raman enhanced efficiency. Here, we synthesized defective graphene (DG) films by chemical vapor deposition on Au, which has a defect density of ~2.0 × 1011 cm-2. The DG shows a much better wettability than PG towards dye solution. Combining with the strong adsorption ability of defects to molecules, DG shows greatly enhanced efficiency than PG with perfect lattice. For example, the detection limit for rhodamine B can reach 2 × 10-9 M for DG while it is on the order of 10-7 M for PG. In addition, DG has high enhancement uniformity and the Au substrate can be reused after electrochemical bubbling transfer. These advantages suggest the great potential of the DG grown on Au for practical applications in environmental monitoring.

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    Review of the atmospheric corrosion of magnesium alloys
    Hongguang Liu, Fuyong Cao, Guang-Ling Song, Dajiang Zheng, Zhiming Shi, Mathew S. Dargusch, Andrej Atrens
    J. Mater. Sci. Technol.. 2019, 35 (9): 2003-2016.   DOI: 10.1016/j.jmst.2019.05.001

    Mg atmospheric corrosion is induced by a thin surface aqueous layer. Controlling factors are microgalvanic acceleration between different phases, protection by a continuous second phase distribution, protection by corrosion products, and degradation of protective layers by aggressive species such as chloride ions. The Mg atmospheric corrosion rate increases with relative humidity (RH) and concentrations of aggressive species. Temperature increases the corrosion rate unless a protective film causes a decrease. O2, SO2 and NO2 accelerate the atmospheric corrosion rate, whereas the corrosion rate is decreased by CO2. The traditional gravimetric method can evaluate effectively the corrosion behavior of Mg alloys.

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    Effects of Mg17Al12 second phase particles on twinning-induced recrystallization behavior in Mg-Al-Zn alloys during gradient hot rolling
    Zhong-Zheng Jin, Xiu-Ming Cheng, Min Zha, Jian Rong, Hang Zhang, Jin-Guo Wang, Cheng Wang, Zhi-Gang Li, Hui-Yuan Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 2017-2026.   DOI: 10.1016/j.jmst.2019.05.017

    This study aims to investigate the promotion effect of twinning-induced nucleation vs the inhibition effect of Mg17Al12 particles pinning for recrystallization, achieved through gradient rolling for Mg-3Al-1Zn (AZ31) and Mg-9Al-1Zn (AZ91) alloys as well as pure Mg. Through gradient rolling, a transition zone from the initial to deformed microstructure undergoing varying thickness reductions was obtained in the same sample, where the evolution of deformation twins and second phase can be examined precisely and continuously. During hot deformation, dynamic recrystallized (DRXed) grains tended to originate from {10$\bar{1}$1}-{10$\bar{1}$2} double twins, whose nucleation was significantly restricted by increasing Al content and hence recrystallization can be rarely triggered in AZ91 alloy. Concurrently, the size and volume fraction of Mg17Al12 particles changed via dissolution and re-precipitation, leading to finer average size and higher volume fraction, which produced stronger pinning effect and hindered dynamic recrystallization significantly. The current study provides insights into the mechanisms responsible for dynamic recrystallization behavior during hot rolling in Mg-Al-Zn alloys.

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    Microstructure and properties of Ti-6Al-4V fabricated by low-power pulsed laser directed energy deposition
    Hua Tan, Mengle Guo, Adam T. Clare, Xin Lin, Jing Chen, Weidong Huang
    J. Mater. Sci. Technol.. 2019, 35 (9): 2027-2037.   DOI: 10.1016/j.jmst.2019.05.008

    Thin-wall structures of Ti-6Al-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward the top of melt pool tail. This resulted in a microstructure mainly composed of long and thin prior epitaxial β columnar grains (average width ≈200 μm). A periodic pattern in epitaxial growth of grains was observed, which was shown to depend upon laser traverse direction. Utilizing this, a novel means was proposed to determine accurately the fusion boundary of each deposited layer by inspection of the periodic wave patterns. As a result it was applied to investigate the influence of thermal cycling on microstructure evolution. Results showed that acicular martensite, α' phase, and a small amount of Widmanst?tten, α laths, gradually converted to elongated acicular α and a large fraction of Widmanst?tten α laths under layer-wise thermal cycling. Tensile tests showed that the yield strength, ultimate tensile strength and elongation of Ti-6Al-4V thin wall in the build direction were 9.1%, 17.3% and 42% higher respectively than those typically observed in forged solids of the same alloy. It also showed the yield strength and ultimate tensile strength of the transverse tensile samples both were $\widetilde{1}$3.3% higher than those from the build direction due to the strengthening effect of a large number of vertical β grain boundaries, but the elongation was 69.7% lower than that of the build direction due to the uneven grain deformation of β grains.

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    Impact of Si addition on high-temperature oxidation behavior of NiAlHf alloys
    Jing Jing, Jian He, Hongbo Guo
    J. Mater. Sci. Technol.. 2019, 35 (9): 2038-2047.   DOI: 10.1016/j.jmst.2019.04.023

    Silicon (Si) and reactive elements (REs) like hafnium (Hf) have favorable effects on improving the high-temperature oxidation resistance. To reveal the interaction effect between them, Si with different contents was added into β-NiAlHf alloy in this study. Cyclic oxidation behavior at 1200 °C was investigated. Results show that Si can increase the Hf-rich precipitates and suppress Hf outward diffusion, thus inhibit the RE effect leading to worse oxidation resistance. However, NiAlHf-5Si alloy exhibited a lower oxidation rate and better spallation resistance mainly because of the existence of micro-cracks and Ni2Al3 phases which provided more rapid diffusion paths for Al3+.

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    A new physical simulation tool to predict the interface of dissimilar aluminum to steel welds performed by friction melt bonding
    T. Sapanathan, N. Jimenez-Mena, I. Sabirov, M.A. Monclús, J.M. Molina-Aldareguía, P. Xia, L. Zhao, A. Simar
    J. Mater. Sci. Technol.. 2019, 35 (9): 2048-2057.   DOI: 10.1016/j.jmst.2019.05.004

    Optimization of the intermetallic layer thickness and the suppression of interfacial defects are key elements to improve the load bearing capacity of dissimilar joints. However, till date we do not have a systematic tool to investigate the dissimilar joints and the intermetallic properties produced by a welding condition. Friction Melt Bonding (FMB) is a recently developed technique for joining dissimilar metals that also does not exempt to these challenges. The FMB of DP980 and Al6061-T6 was investigated using a new physical simulation tool, based on Gleeble thermo-mechanical simulator, to understand the effect of individual parameter on the intermetallic formation. The proposed method demonstrates its capability in reproducing the intermetallic characteristics, including the thickness of intermetallic bonding layer, the morphology and texture of its constituents (Fe2Al5 and Fe4Al13), as well as their nanohardness and reduced modulus. The advantages of physical simulation tool can enable novel developing routes for the development of dissimilar metal joining processes and facilitate to reach the requiring load bearing capacity of the joints.

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    Atomic structure and enhanced thermostability of a new structure MgYZn4 formed by ordered substitution of Y for Mg in MgZn2 in a Mg-Zn-Y alloy
    Lifeng Zhang, Shangyi Ma, Weizhen Wang, Zhiqing Yang, Hengqiang Ye
    J. Mater. Sci. Technol.. 2019, 35 (9): 2058-2063.   DOI: 10.1016/j.jmst.2019.05.013

    A new phase MgYZn4 in Mg-Zn-Y alloy was studied using aberration-corrected scanning-transmission electron microscopy and first-principles calculations. Nanometer-sized MgYZn4 precipitates were formed through ordered substitutions of Y with 50% Mg atoms in MgZn2. MgYZn4 has an orthorhombic structure with a space group of Pmnn, and lattice parameters a =5.2965 ?, b =9.4886 ?, and c =8.5966 ?. Importantly, both size and structure of MgYZn4 are stable at 625 K for 5 h, showing higher thermostability than MgZn2, which should be important for applications at elevated temperatures. The enhanced thermostability of MgYZn4 is attributed to the lower formation energy and bonding enhancement due to Y substitution.

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    Mechanical and thermal properties of RE4Hf3O12 (RE=Ho, Er, Tm) ceramics with defect fluorite structure
    Wanpeng Hu, Yiming Lei, Jie Zhang, Jingyang Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 2064-2069.   DOI: 10.1016/j.jmst.2019.04.025

    The thermal and environmental barrier coatings (T/EBC) are technologically important for advanced propulsion engine system. In this study, RE4Hf3O12 (RE=Ho, Er, Tm) with defect fluorite structure was investigated for potential use as top TBC layer. Dense pellets were fabricated via a hot pressing method and the mechanical and thermal properties were characterized. RE4Hf3O12 (RE=Ho, Er, Tm) possessed a high Vickers hardness of 11 GPa. The material retained high elastic modulus at elevated temperatures up to 1773 K, which made it attractive for high temperature application. The coefficient of thermal expansion (CTE) of RE4Hf3O12 (RE = Ho, Er, Tm) laid in the range between 7 × 10-6 K-1 to 10 × 10-6 K-1 from 473 K to 1673 K. In addition, the rare earth hafnates exhibited lower thermal conductivity which rendered it a good candidate material for thermal barrier applications.

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    Microstructures and mechanical properties of Ti3Al/Ni-based superalloy joints brazed with AuNi filler metal
    H.S. Ren, H.P. Xiong, W.M. Long, B. Chen, Y.X. Shen, S.J. Pang
    J. Mater. Sci. Technol.. 2019, 35 (9): 2070-2078.   DOI: 10.1016/j.jmst.2019.04.015

    For the purpose of high-temperature service and the weight reduction in aviation engineering applications, the dissimilar joining of Ti3Al-based alloy to Ni-based superalloy (GH536) was conducted using Au-17.5Ni (wt%) brazing filler metal. The microstructure and chemical composition at the interfaces were investigated by scanning electron microscope, X-ray diffraction and transmission electron microscope. The diffusion behaviors of elements were analyzed as well. The results indicated that the Ti3Al/GH536 joint microstructure was characterized by multiple layer structures. Element Ni from Au-Ni filler metal reacted with Ti3Al base metal, leading to the formation of AlNi2Ti and NiTi compounds. Element Ni from Ti3Al base metal reacted with Ni and thus Ni3Nb phase was detected in the joint central area. Due to the dissolution of Ni-based superalloy, (Ni,Au) solid solution ((Ni,Au)ss) and Ni-rich phase were visible adjacent to the superalloy side. The average tensile strength of all the joints brazed at 1253 K for 5-20 min was above 356 MPa at room-temperature. In particular, the joints brazed at 1253 K/15 min presented the maximum tensile strength of 434 MPa at room-temperature, and the strength of 314 MPa was maintained at 923 K. AlNi2Ti compound resulted in the highest hardness area and the fracture of the samples subjected to the tensile test mainly occurred in this zone.

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    Serration and shear avalanches in a ZrCu based bulk metallic glass composite in different loading methods
    Haichao Sun, Zhiliang Ning, Jingli Ren, Weizhong Liang, Yongjiang Huang, Jianfei Sun, Xiang Xue, Gang Wang
    J. Mater. Sci. Technol.. 2019, 35 (9): 2079-2085.   DOI: 10.1016/j.jmst.2019.04.014

    In the current research, serrated flow is investigated under tensile and compressive loading in a ZrCu-based bulk metallic glass composite (BMGC) that is well known for its plastic deformability, which is higher than that of metallic glasses. Statistical analysis on serrations shows a complex, scale free process, in which shear bands are highly correlated. The distribution of the elastic-energy density stored in each serration event follows a power-law relationship, showing a randomly generated serrated event under both tension and compression tests. The plastic deformation in the temporal space is explored by a time-series analysis, which is consistent with the trajectory convergent evolution in critical dynamic behavior even in the low strain rate regime in both tests. The results demonstrate that the secondary phase in the BMGC can stabilize the shear band extension and facilitate the critical behavior in the low strain rate regime. This study provides a strong evidence of serrated flow phenomenon in BMGC under tension test, and offers a deep understanding of the correlation between serrations and shear banding in temporal space.

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    Effects of Fe concentration on microstructure and corrosion of Mg-6Al-1Zn-xFe alloys for fracturing balls applications
    Cheng Zhang, Liang Wu, Guangsheng Huang, Lin Chen, Dabiao Xia, Bin Jiang, Andrej Atrens, Fusheng Pan
    J. Mater. Sci. Technol.. 2019, 35 (9): 2086-2098.   DOI: 10.1016/j.jmst.2019.04.012

    Mg-6Al-1Zn-xFe (x = 0, 1, 3, 5 and 7 wt%) alloys were prepared by powder metallurgy and followed by hot extrusion. Majority of Fe element exists as insoluble particles in the alloys. The as-extruded alloys showed higher degradable rates but less stable mechanical properties than as-annealed alloys. Corrosion rate of all the alloys increased with increasing Fe concentration, reaching 2.4 mL cm-2 h-1. 0.2% yield strength of all the alloys was higher than 150 MPa. In short, Mg-6Al-1Zn-xFe alloys have an attractive combination of corrosion and mechanical properties, which holds a bright future for fracturing balls applications.

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    Joining of Cf/SiC composite to GH783 superalloy with NiPdPtAu-Cr filler alloy and a Mo interlayer
    Wen-Wen Li, Bo Chen, Hua-Ping Xiong, Wen-Jiang Zou, Hai-Shui Ren
    J. Mater. Sci. Technol.. 2019, 35 (9): 2099-2106.   DOI: 10.1016/j.jmst.2019.04.011

    With assistance of Mo interlayer, joining of Cf/SiC composite to GH783 superalloy was carried out using NiPdPtAu-Cr filler alloy. Under the brazing condition of 1200 °C for 10 min, the maximum joint strength of 98.5 MPa at room temperature was achieved when the thickness of Mo interlayer was 0.5 mm. Furthermore, the corresponding joint strength tested at 800 °C and 900 °C was even elevated to 123.8 MPa and 133.0 MPa, respectively. On one hand, the good high-temperature joint strength was mainly attributed to the formation of the refractory Mo-Ni-Si ternary compound within the joint. On the other hand, the residual Mo interlayer as a hard buffer, can release the residual thermal stresses within the dissimilar joint. The Cf/SiC-Mo bonding interface was still the weak link over the whole joint, and the cracks propagated throughout the whole reaction zone between the Cf/SiC composite and the Mo interlayer.

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    High strength and high creep resistant ZrB2/Al nanocomposites fabricated by ultrasonic-chemical in-situ reaction
    Xizhou Kai, Shuoming Huang, Lin Wu, Ran Tao, Yanjie Peng, Zemin Mao, Fei Chen, Guirong Li, Gang Chen, Yutao Zhao
    J. Mater. Sci. Technol.. 2019, 35 (9): 2107-2114.   DOI: 10.1016/j.jmst.2019.04.020

    In this study, the ZrB2/Al nanocomposites were fabricated via in-situ reaction of the Al-K2ZrF6-KBF4 system, assisted with ultrasonic vibration and spiral electromagnetic stirring. Microstructure, tensile property and creep behavior of the fabricated nanocomposites were further investigated. Microstructure observation showed that the ultrasonic vibration could prevent the fast growth as well as break the clusters of in-situ synthesized nanoparticles in melt, resulted in smaller size (10-50 nm) and relatively more uniform distribution of the in-situ nanoparticles located on the boundary of and/or inside the aluminum matrix grains in the final composites. The fabricated nanocomposites exhibited an enhancement in both strength and ductility, due to the elevated work hardening ability, i.e., improved dislocation propagating ability and decreased dynamic recovery of the existing dislocations induced by the in-situ nanoparticles. Meanwhile, the nanocomposites exhibited excellent creep resistance ability, which was about 2-18 times higher than those of the corresponding aluminum matrix. The stress exponent of 5 was identified for the fabricated nanocomposites, which suggested that their creep behavior was related to dislocation climb mechanism. The enhanced creep resistance of the nanocomposites was attributed to the Orowan strengthening and grain boundary strengthening induced by the ZrB2 nanoparticles. Thus, the ultrasonic-chemical in-situ reaction promises a low cost but effective way to fabricate aluminum nanocomposites with high strength and high creep resistance.

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    Interpolation and extrapolation with the CALPHAD method
    Qun Luo, Cong Zhai, Dongke Sun, Wei Chen, Qian Li
    J. Mater. Sci. Technol.. 2019, 35 (9): 2115-2120.   DOI: 10.1016/j.jmst.2019.05.016

    It is widely reported that CALPHAD is an extrapolation method when the thermodynamic properties of a multicomponent system are approximated by its subsystems. In this work the meaning of the words extrapolation and interpolation is discussed in context of the CALPHAD method. When assessing the properties in binary and ternary systems, extrapolation method is indeed often used. However, after assessment, the Gibbs energies are in fact interpolated from the lower order systems into the higher order systems in the compositional space. The metastable melting temperatures of bcc and hcp in Re-W and the liquid miscibility gap in Mg-Zr system are predicted to illustrate the difference between interpolation and extrapolation.

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