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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      10 February 2018, Volume 34 Issue 2 Previous Issue    Next Issue
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    Orginal Article
    What is going on in magnesium alloys?
    X.J. Wang, D.K. Xu, R.Z. Wu, X.B. Chen, Q.M. Peng, L. Jin, Y.C. Xin, Z.Q. Zhang, Y. Liu, X.H. Chen, G. Chen, K.K. Deng, H.Y. Wang
    J. Mater. Sci. Technol., 2018, 34 (2): 245-247.  DOI: 10.1016/j.jmst.2017.07.019
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    China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium (Mg) and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin (2015) and Chongqing (2016) China, respectively. A number of crucial research interests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows: i) Plastic deformation mechanism and strengthening strategy, ii) Design and development of new Mg-based materials, iii) Key service properties, and iv) New processing technologies.

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    Hall-Petch relationship in Mg alloys: A review
    Huihui Yu, Yunchang Xin, Maoyin Wang, Qing Liu
    J. Mater. Sci. Technol., 2018, 34 (2): 248-256.  DOI: 10.1016/j.jmst.2017.07.022
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    Grain refinement could effectively enhance yield strength of Mg alloys according to the well-known Hall-Petch theory. For decades, many studies have been devoted to the factors influencing the Hall-Petch slope (k) in Mg alloys. Understanding the factors influencing k and their mechanisms could offer guidance to design and produce high-strength Mg alloys through effective grain refinement hardening. A review and comments of the past work on the factors influencing k in Mg alloys are presented. Results of these previous investigations demonstrate that the value of k in Mg alloys varies with texture, grain size, temperature and stain. The influence of texture and grain size on k is found to be an essential result of the variation of deformation mode on k value. Without the variation of deformation modes, it is revealed that texture could also impose a significant effect on k and this is also summarized and discussed in this paper. The reason for texture effect on k is analyzed based on the mechanism of Hall-Petch relationship. In addition, it is found in face-centered cubic (fcc) or body-centered cubic (bcc) metals that boundary parameters (boundary coherence, boundary energy and boundary diffusivity) could strengthen twinning or slips to a different extent. Therefore, the role of boundary parameters is also extended into the k values in Mg alloys and discussed in this paper. In the end, we discuss the future research perspective of Hall-Petch relationship in Mg alloys.

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    Bimodal microstructure - A feasible strategy for high-strength and ductile metallic materials
    Min Zha, Hong-Min Zhang, Zhi-Yuan Yu, Xuan-He Zhang, Xiang-Tao Meng, Hui-Yuan Wang, Qi-Chuan Jiang
    J. Mater. Sci. Technol., 2018, 34 (2): 257-264.  DOI: 10.1016/j.jmst.2017.11.018
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    Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results on fcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo-mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.

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    Accelerated precipitation behavior of cast Mg-Al-Zn alloy by grain refinement
    Sang-HoonKim, Jong UnLee, Ye JinKim, Jun HoBae, Bong SunYou, Sung HyukPark
    J. Mater. Sci. Technol., 2018, 34 (2): 265-276.  DOI: 10.1016/j.jmst.2017.11.019
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    This study demonstrates that the precipitation behavior of β-Mg17Al12 phase during aging and the resultant variation in hardness and mechanical properties of cast Mg-Al-Zn alloy are strongly dependent on initial grain size. Grain size reduction accelerates discontinuous precipitation at the early stage of aging treatment by increasing the area fraction of grain boundaries that can act as nucleation sites for discontinuous precipitates (DP), but it does not influence DP growth rate. Grain refinement also prematurely terminates continuous precipitation because the formation of a large number of DP reduces the amount of Al dissolved in the matrix, which is required for the formation of continuous precipitates (CP). This promotion of DP formation and early termination of CP formation significantly decrease the peak-aging time to one-third. The enhanced precipitation behavior also leads to an additional hardness improvement in the aged alloy, along with an increase in hardness owing to grain boundary strengthening by grain refinement. The amount of increase in hardness changes with aging time, which is determined by the variation of three variables with aging time: DP fraction difference between refined and nonrefined alloys, hardness difference between DP and matrix, and matrix hardness difference between the two alloys. Grain refinement improves both tensile strength and ductility of the homogenized alloy owing to grain boundary strengthening and suppression of twinning activation, respectively. However, the loss of ductility after peak-aging treatment is greater in the refined alloy because of the larger amount of DP acting as a crack source in this alloy.

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    Influence of size and distribution of W phase on strength and ductility of high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca alloy processed by indirect extrusion
    Hansi Jiang, Xiaoguang Qiao, Chao Xu, Shigeharu Kamado, Kun Wu, Mingyi Zheng
    J. Mater. Sci. Technol., 2018, 34 (2): 277-283.  DOI: 10.1016/j.jmst.2017.11.022
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    A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca (wt%) alloy containing W phase (Mg3Y2Zn3) prepared by permanent mold direct-chill casting is indirectly extruded at 350 °C and 400 °C, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized (DRXed) grains and unrecrystallized coarse regions containing fine W phase and β2? precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350 °C exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400 °C shows lower yield strength of 332 MPa, ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400 °C, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the unDRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of unDRXed regions which contributes to higher strength of the alloy extruded at 350 °C.

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    Heat-treatable Mg-9Al-6Sn-3Zn extrusion alloy
    Chaoqiang Liu, Chenglong Liu, Houwen Chen, Jian-Feng Nie
    J. Mater. Sci. Technol., 2018, 34 (2): 284-290.  DOI: 10.1016/j.jmst.2017.11.012
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    Mg-9Al-6Sn-3Zn (wt%) alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg17Al12 precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg17Al12 nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.

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    Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples
    Jiahong Dai, Hong Xiao, Bin Jiang, Hongmei Xie, Cheng Peng, Zhongtao Jiang, Qin Zou, Qingshan Yang, Fusheng Pan
    J. Mater. Sci. Technol., 2018, 34 (2): 291-298.  DOI: 10.1016/j.jmst.2017.10.007
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    The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al2Ca is the only phase existing in the diffusion reaction layers. The volume fraction of Al2Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350-400 °C, the structure of Al2Ca is more stable than that of Al4Ca, Al14Ca13and Al3Ca8. The growth constants of the layer I, layer II and entire diffusion reaction layers were determined. The activation energies for the growth of the layer I, layer II and entire diffusion reaction layers were (80.74 ± 3.01) kJ/mol, (93.45 ± 2.12) kJ/mol and (83.52 ± 1.50) kJ/mol, respectively. In layer I and II, Al has higher integrated interdiffusion coefficients D?iInt,layer,layer than Ca. The average effective interdiffusion coefficients D?Aleff values are higher than D?Caeff in the layer I and II.

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    Effect of trace HA on microstructure, mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy
    Jian-Xing Li, Yuan Zhang, Jing-Yuan Li, Jian-Xin Xie
    J. Mater. Sci. Technol., 2018, 34 (2): 299-310.  DOI: 10.1016/j.jmst.2017.06.013
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    Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites (x = 0, 0.1 and 0.3 wt%) were characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). Results of tensile tests at room temperature show that yield strength (YS) of Mg-2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength (UTS) and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential (Ecorr) of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from -1724 to -1660 mVSCE and the corrosion current density decreases from 479.8 to 280.8 μA cm-2 with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.5Sr/HA composites decreases from 11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO4 protective film due to the adsorption of Ca2+ on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.

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    Nanoscale deformation of multiaxially forged ultrafine-grained Mg-2Zn-2Gd alloy with high strength-high ductility combination and comparison with the coarse-grained counterpart
    counterpartK. Li, V.S.Y. Injeti, P. Trivedi, L.E. Murr, R.D.K. Misra
    J. Mater. Sci. Technol., 2018, 34 (2): 311-316.  DOI: 10.1016/j.jmst.2017.07.023
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    Cold processing of magnesium (Mg) alloys is a challenge because Mg has a hexagonal close-packed (HCP) lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To address this challenge, a combination of annealing of as-cast alloy and multi-axial forging was adopted to obtain isotropic ultrafine-grained (UFG) structure in a lean Mg-2Zn-2Gd alloy with high strength (yield strength: ~227 MPa)-high ductility (% elongation: ~30%) combination. This combination of strength and ductility is excellent for the lean alloy, enabling an understanding of deformation processes in a formable high strength Mg-rare earth alloy. The nanoscale deformation behavior was studied via nanoindentation and electron microscopy, and the behavior was compared with its low strength (yield strength: ~46 MPa) - low ductility (% elongation: ~7%) coarse-grained (CG) counterpart. In the UFG alloy, extensive dislocation slip was an active deformation mechanism, while in the CG alloy, mechanical twinning occurred. The differences in the deformation mechanisms of UFG and CG alloys were reflected in the discrete burst in the load-displacement plots. The deformation of Mg-2Zn-2Gd alloys was significantly influenced by the grain structure, such that there was change in the deformation mechanism from dislocation slip (non-basal slip) to nanoscale twins in the CG structure. The high plasticity of UFG Mg alloy involved high dislocation activity and change in activation volume.

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    Microstructure and mechanical properties of Mg-5Li-1Al sheets prepared by accumulative roll bonding
    bondingLegan Hou, Tianzi Wang, Ruizhi Wu, Jinghuai Zhang, Milin Zhang, Anping Dong, Baode Sun, Sergey Betsofen, Boris Krit
    J. Mater. Sci. Technol., 2018, 34 (2): 317-323.  DOI: 10.1016/j.jmst.2017.02.005
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    Ultrafine-grain and high-strength Mg-5Li-1Al sheets were prepared by accumulative roll bonding (ARB) process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated.Results show that, during ARB process, the evolution of deformation mechanism of t Mg-5Li-1Al alloy is as follows: twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization (DRX). The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.

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    Grain Size Distribution and Interfacial Heat Transfer Coefficient during Solidification of Magnesium Alloys Using High Pressure Die Casting Process
    P. Sharifi, J. Jamali, K. Sadayappan, J.T. Wood
    J. Mater. Sci. Technol., 2018, 34 (2): 324-334.  DOI: 10.1016/j.jmst.2016.09.004
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    The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCAST?, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting. Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interfacial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interfacial heat transfer coefficient for different locations.

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    Influence of electric field on the quenched-in vacancy and solute clustering during early stage ageing of Al-Cu alloy
    Shang Fu, Ying Zhang, Huiqun Liu, Danqing Yi, Bin Wang, Yong Jiang, Zhiquan Chen, Ning Qi
    J. Mater. Sci. Technol., 2018, 34 (2): 335-343.  DOI: 10.1016/j.jmst.2017.07.020
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    The effects of electric field on the evolution of excess quenched-in vacancy as well as solute clustering in Al-4wt%Cu alloy, and on the vacancy migration and formation enthalpy of pure aluminum were investigated, using positron annihilation lifetime spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, transmission electron microscopy, hardness measurement and four-probe electrical resistivity measurement. The results showed that the electric field improved age hardening response obviously and postponed the decay of excess vacancies for 30 min during the early stage ageing of Al-4wt%Cu alloy. A large number of 2-4 nm GP zones with dense distribution were observed after 1 min ageing with an electric field applied. The electric field-assisted-aged sample owned a lower coarsening rate of GP zone, which was about three fifths of that in the aged sample without an electric field, from 1 min to 120 min ageing. The electric field contributed 8% increase of the vacancy migration enthalpy (0.663 ± 0.021 eV) of pure Al, comparing with that (0.611 ± 0.023 eV) of pure Al without an electric field. The increase of vacancy migration enthalpy, induced by the electric field, was responsible for the difference on evolution of quenched-in vacancy, rapid solute clustering and age hardening improvement during the early stage ageing of Al-4wt%Cu alloy.

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    A promising new class of plasticine: Metallic plasticine
    Yiping Lu, Zhongyi Tang, Bin Wen, Gang Wang, Shiwei Wu, Tongmin Wang, Yubo Zhang, Zongning Chen, Zhiqiang Cao, Tingju Li
    J. Mater. Sci. Technol., 2018, 34 (2): 344-348.  DOI: 10.1016/j.jmst.2017.06.022
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    Soft, malleable, and non-dry on exposure in air are the typical features for plain plasticine, which lead plasticine to be widely used in many industrial fields and our daily life. As a kind of clay, poorly electric conductivity and thermal conductivity of plain plasticine seriously limit its applications. Therefore, synthesizing a kind of plasticine having metallic bond is of importance for extending its applications in some special cases, such as thermal-cooling medium, anti-static electricity, electromagnetic shielding, etc. Here, we report a novel GaInSnCdZn2 alloy, which exhibits similar behavior as compared to those of plasticine at near room temperature (30-40 °C), and a good electrical conductivity due to its nature of metal. This new GaInSnCdZn2 alloy can be called as metallic plasticine that contains the near-eutectic structure with low melting point and the other relatively high melting point phases. In this metallic plasticine, the near-eutectic structure with low melting point plays the same role as the oily ingredient in plain plasticine, dominating the plastic deformation, while the other relatively high melting point phases act as the stuffing like the CaCO3 in plain plasticine. The creation of metallic plasticine offers a general strategy for designing/preparing a new class of plasticine which possesses both the nature of metal and plasticine.

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    Effect of lattice distortion on solid solution strengthening of BCC high-entropy alloys
    Zhipeng Wang, Qihong Fang, Jia Li, Bin Liu, Yong Liu
    J. Mater. Sci. Technol., 2018, 34 (2): 349-354.  DOI: 10.1016/j.jmst.2017.07.013
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    :An analytical model is established to study the influence of lattice distortion and fraction of Hf on the yield strength of the BCC TiNbTaZrHfx multi-component high entropy alloys (HEAs). Meanwhile, the mechanism of solid solution strengthening caused by lattice distortion is also discussed in the HEA. The distorted unit cell is introduced to indicate the lattice distortion effects induced by the differences of the atomic size and shear modulus by doping other elements in Ti-based metal. The results show that the calculated values of the alloying yield strength considering the path of least resistance are obtained with regard to various grain sizes for the equiatomic TiNbTaZrHf HEA, which is well in line with the experimental results. Furthermore, it is predicted that the alloying yield strength is the largest value in the case of the same grain size for the Hf atomic fraction of 0.122. The meaningful modeling could provide a theoretical method to investigate the yield strength and alloying design of other BCC HEAs in the future.

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    Vacancy formation enthalpies of high-entropy FeCoCrNi alloy via first-principles calculations and possible implications to its superior radiation tolerance
    Weiliang Chen, Xueyong Ding, Yuchao Feng, Xiongjun Liu, Kui Liu, Z.P. Lu, Dianzhong Li, Yiyi Li, C.T. Liu, Xing-Qiu Chen
    J. Mater. Sci. Technol., 2018, 34 (2): 355-364.  DOI: 10.1016/j.jmst.2017.11.005
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    Because atoms in high-entropy alloys (HEAs) coordinate in very different and distorted local environments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities (i.e., defect formation enthalpies) of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory (DFT) in combination of special quasi-random structure models (SQSs), we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88-2.90 eV for Co, 0.78-3.09 eV for Cr, and 0.91-2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that (1.41 eV) of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.

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    Microstructures and mechanical properties of Nb-alloyed CoCrCuFeNi high-entropy alloys
    Gang Qin, Shu Wang, Ruirun Chen, Xue Gong, Liang Wang, Yanqing Su, Jingjie Guo, Hengzhi Fu
    J. Mater. Sci. Technol., 2018, 34 (2): 365-369.  DOI: 10.1016/j.jmst.2017.11.007
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    Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys (HEAs) with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the (CoCrCuFeNi)100-xNbx HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC (face-centered cubic) to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases. Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of (CoCrCuFeNi)100-xNbx HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% (no fracture) to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC (valence electron concentration) value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.

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    Structures and electrochemical performances of as-spun RE-Mg-Ni-Co-Al alloys applied to Ni-MH battery
    Yanghuan Zhang, Songsong Cui, Yaqin Li, Hongwei Shang, Yan Qi, Dongliang Zhao
    J. Mater. Sci. Technol., 2018, 34 (2): 370-378.  DOI: 10.1016/j.jmst.2017.06.016
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    The La-Mg-Ni-Co-Al-based AB2-type La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) alloys were prepared by melt spinning. The effects of Y content on the structures and electrochemical hydrogen storage characters were thoroughly studied. The structures of the experimental samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is shown that there are a main phase LaMgNi4 and a second phase LaNi5 in the experimental samples. The variation of Y content incurs obvious changes of the phase abundance without changing phase composition. Namely, with the increase of Y content, the LaMgNi4 phase increases and LaNi5 phase decreases. Furthermore, melt spinning and the replacement of Y for La also lead to the grains refinement of the alloy. The electrochemical tests display that the as-spun alloys possess excellent activation properties, and obtain the maximums of discharge capacity at the first cycling. The replacement of Y for La can visibly facilitate the discharge potential characteristics, however,diminish the discharge capacity. The electrochemical kinetics, involving in the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (IL) and charge transfer rate, increases firstly and then decreases with the increase of Y content. The cyclic stability is greatly improved by melt spinning and the replacement of Y for La, which is derived from the improvement of the anti-corrosion, oxidation-resistance and the anti-pulverization abilities.

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    Preparation and characterization of capric-palmitic-stearic acid ternary eutectic mixture/expanded vermiculite composites as form-stabilized thermal energy storage materials
    Weiyi Zhang, Xiaoguang Zhang, Zhaohui Huang, Zhaoyu Yin, Ruilong Wen, Yaoting Huang, Xiaowen Wu, Xin Min
    J. Mater. Sci. Technol., 2018, 34 (2): 379-386.  DOI: 10.1016/j.jmst.2017.06.003
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    In this study, a composite of form-stable phase change materials (FSPCMs) were prepared by the incorporation of a eutectic mixture of capric-palmitic-stearic acid (CA-PA-SA) into expanded vermiculite (EV) via vacuum impregnation. In the composites, CA-PA-SA was utilized as a thermal energy storage material, and EV served as the supporting material. X-ray diffraction and Fourier transform infrared spectroscopy results demonstrated that CA-PA-SA and EV in the composites only undergo physical combination, not a chemical reaction. Scanning electron microscopy images indicated that CA-PA-SA is sufficiently absorbed in the expanded vermiculite porous network. According to differential scanning calorimetry results, the 70 wt% CA-PA-SA/EV sample melts at 19.3 °C with a latent heat of 117.6 J/g and solidifies at 17.1 °C with a latent heat of 118.3 J/g. Thermal cycling measurements indicated that FSPCMs exhibit adequate stability even after being subjected to 200 melting-freezing cycles. Furthermore, the thermal conductivity of the composites increased by approximately 49.58% with the addition of 5 wt% of Cu powder. Hence, CA-PA-SA/EV FSPCMs are effective latent heat thermal energy storage building materials.

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    Glycidyl methacrylate-compatibilized poly(lactic acid)/hemp hurd biocomposites: Processing, crystallization, and thermo-mechanical response
    Belas Ahmed Khan, Haining Na, Venkata Chevali, Philip Warner, Jin Zhu, Hao Wang
    J. Mater. Sci. Technol., 2018, 34 (2): 387-397.  DOI: 10.1016/j.jmst.2017.03.004
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    Poly(lactic acid)-based biocomposites were developed with hemp hurd (Cannabis sativa L.) with grafting-based interfacial compatibilization. Poly(lactic acid) was extruded with hemp hurd and glycidyl methacrylate as the polymer/hurd interfacial compatibilizer, and injection molded. Interfacial compatibility between poly(lactic acid) and hemp hurd increased with grafted glycidyl methacrylate in comparison to the non-compatibilized control, as corroborated by scanning electron microscopy fractography and mechanical analysis, which showed increases in the glycidyl methacrylate-grafted 20% (w/w) hemp hurd/poly(lactic acid) biocomposite, retaining 94% of the neat polymer strength, with increases in crystallinity, and showing a range of thermo-mechanical properties desirable for rigid biocomposite applications.

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    Microstructure and secondary phases in epitaxial LaBaCo2O5.5 + δ thin films
    Jiangbo Lu, Lu Lu, Sheng Cheng, Ming Liu, Chunlin Jia
    J. Mater. Sci. Technol., 2018, 34 (2): 398-402.  DOI: 10.1016/j.jmst.2016.09.027
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    Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5 + δ (LBCO) thin films grown on SrTiO3 (STO) substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and (001)LBCO//(001)STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 °C, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 °C, isolated nano-scale Co3O4 particles appeared, which promoted the growth of {111} twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.

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    Syngas production via coal char-CO2 fluidized bed gasification and the effect on the performance of LSCFN//LSGM//LSCFN solid oxide fuel cell
    cellHai-Bin Li, Na Xu, Yi-Hua Fang, Hui Fan, Ze Lei, Min-Fang Han
    J. Mater. Sci. Technol., 2018, 34 (2): 403-408.  DOI: 10.1016/j.jmst.2017.06.001
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    Fluidized bed reactor is widely used in coal char-CO2 gasification. In this work, the production of syngas by using a fluidized bed gasification technique was first investigated and then the effect of the produced syngas on the performance of the solid oxide fuel cell with a configuration of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ//La0.8Sr0.2Ga0.83Mg0.17O3-δ//La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ(LSCFN//LSGM//LSCFN) was studied. During the syngas production, we found that the volume fraction of CO increased with the increment of gasification temperature, and it reached a maximum value of 88.8%, corresponding to a composition of 0.76% H2, 88.8% CO, and 10.44% CO2, when the ratio of oxygen mass flow rate to that of coal char (MO2/Mchar) increased to 0.29. In the following utilization of the produced syngas in solid oxide fuel cells, it was found that the increasing CO volume fraction in the syngas results in a gradual increase of the peak power density of the LSCFN//LSGM//LSCFN cell. The maximum peak power density of 410 mW/cm2 was achieved for the syngas produced at 0.29 of MO2/Mchar. In the stability test, the cell voltage decreased by 4% at a constant current density of 0.475 A/cm2 after 54 h when fueled with the syngas with the composition of 0.76% H2, 88.8% CO, and 10.44% CO2. It reveals that a carbon deposition with the content of 13.66% in the anode is attributed to the cell performance degradation.

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    Influence of cryogenic thermal cycling treatment on the thermophysical properties of carbon/carbon composites between room temperature and 1900 °C
    Mao-yan Zhang, Ke-zhi Li, Xiao-hong Shi, Ling-jun Guo, Lei Feng, Tao DuanState
    J. Mater. Sci. Technol., 2018, 34 (2): 409-415.  DOI: 10.1016/j.jmst.2017.03.001
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    Influence of cryogenic thermal cycling treatment (from -120 °C to 120 °C at 1.3 × 10-3 Pa) on the thermophysical properties including thermal conductivity (TC), thermal diffusivity (TD), specific heat (SH) and coefficient of thermal expansion (CTE) ranging from room temperature to 1900 °C of carbon/carbon (C/C) composites in x-y and z directions were studied. Test results showed that fiber/matrix interfacial debonding, fiber pull-out and microcracks occurred after the cryogenic thermal treatment and they increased significantly with the cycle number increasing, while cycled more than 30 times, the space of microdefects reduced obviously due to the accumulation of cyclic thermal stress. TC, TD, SH and CTE of the cryogenic thermal cycling treated C/C composites were first decreased and then increased in both directions (x-y and z directions) with the increase of thermal cycles. A model regarding the heat conduction in cryogenic thermal cycling treated C/C composites was proposed.

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