Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      01 January 2020, Volume 36 Issue 0 Previous Issue    Next Issue
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    Research Article
    Microstructure and mechanical properties of novel Al-Y-Sc alloys with high thermal stability and electrical conductivity
    A.V. Pozdniakov, R.Yu. Barkov
    J. Mater. Sci. Technol., 2020, 36 (0): 1-6.  DOI: 10.1016/j.jmst.2019.08.006
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    The microstructure and mechanical properties of novel Al-Y-Sc alloys with high thermal stability and electrical conductivity were investigated. Eutectic Al3Y-phase particles of size 100-200 nm were detected in the as-cast microstructure of the alloys. Al3Y-phase particles provided a higher hardness to as cast alloys than homogenized alloys in the temperature range of 370-440 °C. L12 precipitates of the Al3(ScxYy) phase were nucleated homogenously within the aluminium matrix and heterogeneously on the dislocations during annealing at 400 °C. The average size of the L12 precipitates was 11±2 nm after annealing for 1 h, and 25-30 nm after annealing for 5 h, which led to a decrease in the hardness of the Al-0.2Y-0.2Sc alloy to 15 HV. The recrystallization temperature exceeded 350 °C and 450 °C for the Al-0.2Y-0.05Sc and Al-0.2Y-0.2Sc alloys, respectively. The investigated alloys demonstrated good thermal stability of the hardness and tensile properties after annealing the rolled alloys at 200 and 300 °C, due to fixing of the dislocations and grain boundaries by L12 precipitates and eutectic Al3Y-phase particles. The good combination of strength, plasticity, and electrical conductivity of the investigated Al-0.2Y-0.2Sc alloys make it a promising candidate for electrical conductors. The alloys exhibited a yield stress of 177-183 MPa, ultimate tensile stress of 199-202 MPa, elongation of 15.2-15.8%, and electrical conductivity of 60.8%-61.5% IACS.

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    Microstructural evolution and defect formation in a powder metallurgy nickel-based superalloy processed by selective laser melting
    Hongyu Wu, Dong Zhang, Biaobiao Yang, Chao Chen, Yunping Li, Kechao Zhou, Liang Jiang, Ruiping Liu
    J. Mater. Sci. Technol., 2020, 36 (0): 7-17.  DOI: 10.1016/j.jmst.2019.08.007
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    In this study, the selective laser melting (SLM) technology has been employed to manufacture a nickel-based superalloy which was conventionally prepared through powder metallurgy (PM) route. The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart. Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point (γ + γ’) eutectic played a vital role in their formation mechanism. Columnar grains oriented along building direction were ubiquitous, corresponding to strong <001> fiber texture. Solidification cell structures and melt pools are pervasive and no γ’ precipitates were detected at about 10 nm scale before heat treatment. After super-solvus solution and two-step aging treatments, high volume fraction γ’ precipitates emerged and their sizes and morphologies were comparable to those in PM alloy. <001> texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events. Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization. Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.

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    Microstructure and mechanical properties of Al-12Si and Al-3.5Cu-1.5Mg-1Si bimetal fabricated by selective laser melting
    P. Wang, C.S. Lao, Z.W. Chen, Y.K. Liu, H. Wang, H. Wendrock, J. Eckert, S. Scudino
    J. Mater. Sci. Technol., 2020, 36 (0): 18-26.  DOI: 10.1016/j.jmst.2019.03.047
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    An Al-12Si/Al-3.5Cu-1.5Mg-1Si bimetal with a good interface was successfully produced by selective laser melting (SLM). The SLM bimetal exhibits four successive zones along the building direction: an Al-12Si zone, an interfacial zone, a texture-strengthening zone and an Al-Cu-Mg-Si zone. The interfacial zone (< 0.2 mm thick) displays an increasing size of the cells composed of eutectic Al-Si and a discontinuous cellular microstructure, resulting in the lowest hardness of the four zones. The texture-strengthening zone (around 0.3 mm thick) shows a remarkable variation of the hardness and <001> fiber texture. Electron backscatter diffraction analysis shows that the grains grow gradually from the interfacial zone to the Al-Cu-Mg-Si zone along the building direction. Additionally, a strong <001> fiber texture develops at the Al-Cu-Mg-Si side of the interfacial zone and disappears gradually along the building direction. The bimetal exhibits a room temperature yield strength of 267 ± 10 MPa and an ultimate tensile strength of 369 ± 15 MPa with elongation of 2.6% ± 0.1%, revealing the potential of selective laser melting in manufacturing dissimilar materials.

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    Synergistic effects of Mg-substitution and particle size of chicken eggshells on hydrothermal synthesis of biphasic calcium phosphate nanocrystals
    Wei Cui, Qibin Song, Huhu Su, Zhiqing Yang, Rui Yang, Na Li, Xing Zhang
    J. Mater. Sci. Technol., 2020, 36 (0): 27-36.  DOI: 10.1016/j.jmst.2019.04.038
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    Magnesium (Mg2+) ion plays important roles in biomineralization of bone, teeth and calcium carbonate skeletons. Herein, chicken eggshells mainly comprising of Mg-calcite nanocrystals (Mg/(Mg + Ca) 2.0 mol.%) were used to fabricate biphasic calcium phosphate (BCP), a mixture of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) nanocrystals, through hydrothermal reactions at 200 °C for 24 h. Our results indicated that β-TCP nanocrystals formed through the ion-exchange reactions of Mg-calcite, while HA nanocrystals were mainly produced by dissolution-reprecipitation reactions on the surfaces of eggshell samples in the hydrothermal system. Mg substitution in calcite resulted in formation of β-TCP nanocrystals instead of HA crystals through ion-exchange reactions. BCP samples with different compositions (28.6-77.8 wt.% β-TCP) were produced by controlling particle sizes of eggshells for hydrothermal reactions. The larger particles lead to the larger proportion of β-TCP in the BCP composition. Therefore, Mg substitution and particle size had synergetic effects on the hydrothermal synthesis of BCP using chicken eggshells through balance of ion-exchange and dissolution-reprecipitation reactions. Cell culture results showed that the BCP products were non-cytotoxic to MC3T3-E1 cells, which may be used for bone substitute materials in future.

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    Correlation of surface features with corrosion behaviors of interstitial free steel processed by temper rolling
    Heng Chen, Zebang He, Lin Lu
    J. Mater. Sci. Technol., 2020, 36 (0): 37-44.  DOI: 10.1016/j.jmst.2019.06.011
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    Temper rolling, as a final manufacturing procedure, brings the change of surface features and hence affects the corrosion behaviors of interstitial-free (IF) steel. This study investigates changes in residual stress, microstructure, and surface topography of IF steel using X-ray diffraction, electron backscatter diffraction, and optical interferometric microscopy. And the synthetic influence of surface features on the corrosion process of the steel was evaluated by damp heat tests and electrochemical measurements. Results showed that low tensile and compressive residual stresses are introduced to the surface of the IF steel. Some grains had a grain orientation spread (GOS) value greater than 0.5° after temper rolling. Moreover, temper rolling caused a slight change in the surface profile of the IF steel. The compressive residual stress had an overwhelming role at the macroscopic level, in retarding the corrosion evolution process of IF steel, as well as in decreasing the average corrosion rate. And corrosion was more likely to initiate and propagate in matrices with a high GOS value, which played the determinant role at the microscopic level. Moreover, the depth of valley in the surface profile could affect the diffusion process involved in the electrode reactions, which was more likely to exert an extra influence on the corrosion rate of IF steel.

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    Gradient microstructure and enhanced mechanical performance of magnesium alloy by severe impact loading
    Maryam Jamalian, David P.Field
    J. Mater. Sci. Technol., 2020, 36 (0): 45-49.  DOI: 10.1016/j.jmst.2019.06.013
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    Subjecting a workpiece to a surface treatment with severe impact loading is a novel severe plastic deformation procedure to fabricate gradient microstructures through the thickness and longitudinal direction. Mechanical performance is a function of twin density and the newly-formed grain size gradients. {10$\bar{1}$2} tensile twins created from processing without excessive grain refinement lead to strength enhancement with retained ductility. Creation of residual strain by a single impact results in a significant reduction in time and cost of the process. This paper investigates the effect of applying severe impact loading on mechanical and microstructural properties of magnesium for various impact velocities.

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    Towards the diffusion source cost reduction for NdFeB grain boundary diffusion process
    H.X. Zeng, Z.W. Liu, J.S. Zhang, X.F. Liao, H.Y. Yu
    J. Mater. Sci. Technol., 2020, 36 (0): 50-54.  DOI: 10.1016/j.jmst.2019.08.009
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    Aiming at improving the performance/cost ratio in grain boundary diffusion process (GBDP), the critical RE containing Pr-Al-Cu alloy, less expensive RE containing La-Al-Cu alloy and non-RE Al-Cu alloy were employed as the diffusion sources. The preliminary results show that the coercivity was successfully enhanced from 1000 kA/m to 1695, 1156 and 1125 kA/m by Pr70Al20Cu10, La70Al20Cu10 and Al75Cu25 (at.%) alloys diffusion, respectively, due to the formation of (Nd,Pr)-Fe-B, La2O3 and c-Nd2O3 phases respectively, after diffusion. It is also found that the corrosion resistance can be improved by Al-Cu diffusion due to the positive effects of Al and Cu elements in grain boundary. The present results demonstrated the various coercivity enhancement mechanisms for the GBDP based on different diffusion sources, and provided feasible solutions for cost reduction of GBDP and NdFeB production by saving RE resource.

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    Interaction between sulfate-reducing bacteria and aluminum alloys—Corrosion mechanisms of 5052 and Al-Zn-In-Cd aluminum alloys
    Fang Guan, Jizhou Duan, Xiaofan Zhai, Nan Wang, Jie Zhang, Dongzhu Lu, Baorong Hou
    J. Mater. Sci. Technol., 2020, 36 (0): 55-64.  DOI: 10.1016/j.jmst.2019.07.009
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    Microbiologically influenced corrosion caused by sulfate-reducing bacteria (SRB) poses a serious threat to marine engineering facilities. This study focused on the interaction between the corrosion behavior of two aluminum alloys and SRB metabolic activity. SRB growth curve and sulfate variation with and with aluminum were performed to find the effect of two aluminum alloys on SRB metabolic activity. Corrosion of 5052 aluminum alloy and Al-Zn-In-Cd aluminum alloy with and without SRB were performed. The results showed that both the presence of 5052 and Al-Zn-In-Cd aluminum alloy promoted SRB metabolic activity, with the Al-Zn-In-Cd aluminum alloy having a smaller promotion effect compared with 5052 aluminum alloy. The electrochemical results suggested that the corrosion of the Al-Zn-In-Cd aluminum alloy was accelerated substantially by SRB. Moreover, SRB led to the transformation of Al-Zn-In-Cd aluminum alloy corrosion product from Al(OH)3 to Al2S3 and NaAlO2.

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    Tensile ductility and deformation mechanisms of a nanotwinned 316L austenitic stainless steel
    Y.Z. Zhang, J.J. Wang, N.R. Tao
    J. Mater. Sci. Technol., 2020, 36 (0): 65-69.  DOI: 10.1016/j.jmst.2019.02.008
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    A nanotwinned 316L austenitic stainless steel was prepared by means of surface mechanical grinding treatment. After recovery annealing, the density of dislocations decreases obviously while the average twin/matrix lamella thickness still keeps in the nanometer scale. The annealed nanotwinned sample exhibits a high tensile yield strength of 771 MPa and a considerate uniform elongation of 8%. TEM observations showed that accommodating more dislocations and secondary twinning inside the nanotwins contribute to the enhanced ductility and work hardening rate of the annealed nanotwinned sample.

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    Ultralight three-dimensional, carbon-based nanocomposites for thermal energy storage
    Oluwafunmilola Ola, Yu Chen, Qijian Niu, Yongde Xia, Tapas Mallick, Yanqiu Zhu
    J. Mater. Sci. Technol., 2020, 36 (0): 70-78.  DOI: 10.1016/j.jmst.2019.06.014
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    Polymer based nanocomposites consisting of elastic three-dimensional (3D) carbon foam (CF), paraffin wax and graphene nanoplatelets (GNPs) have been created and evaluated for thermal energy storage. The ultralight, highly porous (~98.6% porosity), and flexible CFs with densities of 2.84-5.26 mg/cm3 have been used as the backbone skeleton to accommodate phase change wax and nanoscale thermal conductive enhancer, GNP. Low level of defects and the ordered sp2 configuration allow the resulting CFs to exhibit excellent cyclic compressive behavior at strains up to 95%, while retaining part of their elastic properties even after 100 cycles of testing. By dispersing the highly conductive GNP nanofillers in paraffin wax and infiltrating them into the flexible CFs, the resultant nanocomposites were observed to possess enhanced overall thermal conductivity up to 0.76 W/(m K), representing an impressive improvement of 226%, which is highly desirable for thermal engineering.

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    Electron force-induced dislocations annihilation and regeneration of a superalloy through electrical in-situ transmission electron microscopy observations
    Xin Zhang, Hongwei Li, Mei Zhan, Zebang Zheng, Jia Gao, Guangda Shao
    J. Mater. Sci. Technol., 2020, 36 (0): 79-83.  DOI: 10.1016/j.jmst.2019.08.008
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    What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was directly observed by electrical in-situ transmission electron microscopy in this work. Dislocations annihilation at first and then regeneration was found for the first time, which directly proves the existence of electron force during the electrically-assisted manufacturing. Dislocations regeneration would be driven by the electron force and the resistance softening by the local Joule heating effect. Resultantly, a base could be provided for future electrically-assisted research.

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    Synthesis of W-Y2O3 alloys by freeze-drying and subsequent low temperature sintering: Microstructure refinement and second phase particles regulation
    Weiqiang Hu, Zhi Dong, Liming Yu, Zongqing Ma, Yongchang Liu
    J. Mater. Sci. Technol., 2020, 36 (0): 84-90.  DOI: 10.1016/j.jmst.2019.08.010
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    In this work, W-Y2O3 alloys are prepared by freeze-drying and subsequent low temperature sintering. The average size of reduced W-Y2O3 composite powders prepared by freeze-drying method is only 18.1 nm. After low temperature sintering of these composite nanopowders, the formed W-Y2O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%. Besides a few submicron Y2O3 particles (about 100-300 nm) with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries, lots of nano Y2WO6 particles (<20 nm) exist in W matrix. Moreover, many Y6WO12 (<10 nm) particles exist within submicron Y2O3 particles. The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases, resulting in the purification of W matrix and the strengthening of phase boundaries. The combined action of the above factors makes the hardness of the sintered W-Y2O3 alloys in our work as high as 656.6 ± 39.0 HV0.2. Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2O3 alloys.

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    Precipitates and alloying elements distribution in near α titanium alloy Ti65
    Ke Yue, Jianrong Liu, Haijun Zhang, Hui Yu, Yuanyuan Song, Qingmiao Hu, Qingjiang Wang, Rui Yang
    J. Mater. Sci. Technol., 2020, 36 (0): 91-96.  DOI: 10.1016/j.jmst.2019.03.018
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    Precipitates, including silicides and Ti3Al (α2) phase, and alloying elements distribution in a near α titanium alloy Ti65 (Ti-5.8Al-4.0Sn-3.5Zr-0.5Mo-0.3Nb- 1.0Ta-0.4Si-0.8W-0.05C) after solution treatment and aging process were characterized by using transmission electron microscopy (TEM) and atom probe tomography (APT). Quantitative composition analysis and TEM observation indicate that the silicides fit to (Ti, Zr)6(Si, Sn)3. Zr exhibits a β-stabilizing effect in near α titanium alloys but is weaker than other β stabilizing elements. The enriching tendency of the alloying elements in the retained β phase is in the order of Zr < Nb < Ta < Mo < W. The experimental results are rationalized by the relative stability of alloying elements in the α and β phases and the mobility of these atoms in the matrix. An enrichment of Si in the α2 phase over the α matrix phase is noticed, which is attributed to the lower formation energy of Si in the α2 phase.

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    Construction of novel TiO2/Bi4Ti3O12/MoS2 core/shell nanofibers for enhanced visible light photocatalysis
    Meng-Jie Chang, Wen-Na Cui, Jun Liu, Kang Wang, Hui-Ling Du, Lei Qiu, Si-Meng Fan, Zhen-Min Luo
    J. Mater. Sci. Technol., 2020, 36 (0): 97-105.  DOI: 10.1016/j.jmst.2019.06.020
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    TiO2/Bi4Ti3O12 hybrids have been widely prepared as promising photocatalysts for decomposing organic contaminations. However, the insufficient visible light absorption and low charge separation efficiency lead to their poor photocatalytic activity. Herein, a robust methodology to construct novel TiO2/Bi4Ti3O12/MoS2 core/shell structures as visible light photocatalysts is presented. Homogeneous bismuth oxyiodide (BiOI) nanoplates were immobilized on electrospun TiO2 nanofiber surface by successive ionic layer adsorption and reaction (SILAR) method. TiO2/Bi4Ti3O12 core/shell nanofibers were conveniently prepared by partial conversion of TiO2 to high crystallized Bi4Ti3O12 shells through a solid-state reaction with BiOI nanoplates, which is accompanied with certain transition of TiO2 from anatase to rutile phase. Afterwards, MoS2 nanosheets with several layers thick were uniform decorated on the TiO2/Bi4Ti3O12 fiber surface resulting in TiO2/Bi4Ti3O12/MoS2 structures. Significant enhancement of visible light absorption and photo-generated charge separation of TiO2/Bi4Ti3O12 were achieved by introduction of MoS2. As a result, the optimized TiO2/Bi4Ti3O12/MoS2-2 presents 60% improvement for photodegrading RhB after 120 min irradiation under visible light and 3 times higher of apparent reaction rate constant in compared with the TiO2/Bi4Ti3O12. This synthetic method can also be used to establish other photocatalysts simply at low cost, therefore, is suitable for practical applications.

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    Development of gradient microstructure in the lattice structure of AlSi10Mg alloy fabricated by selective laser melting
    Mulin Liu, Naoki Takata, Asuka Suzuki, Makoto Kobashi
    J. Mater. Sci. Technol., 2020, 36 (0): 106-117.  DOI: 10.1016/j.jmst.2019.06.015
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    To identify the microstructural features of the lattice structures of Al alloys built via the selective laser melting (SLM) process, AlSi10Mg alloy with a body-centered cubic (BCC)-type lattice structure was prepared. Characteristic microstructures comprising melt pools with several columnar α-Al phases with <001 > orientations along the elongation direction and surrounded by eutectic Si particles were observed at all portions of the built lattice structure. In the node portions of the lattice structure, a gradient microstructure (continuous change in microstructure) was observed. The columnar α-Al phases were observed near the top surface of the node portion, whereas they became coarser and more equiaxed near the bottom surface, resulting in softening localized near the bottom surface. In the strut portions of the lattice structure, the columnar α-Al phases were elongated along the inclined direction of struts. This trend was more prevalent near the bottom surface. The α-Al phases became coarser and more equiaxed near the bottom surface as well. The aforementioned results were the basis of a discussion of the development of the gradient microstructure in lattice-structured Al alloys during the SLM process in terms of thermal conductivities at the boundaries between the manufactured (locally melted and rapidly solidified) portions and adjacent (unmelted) alloy powder.

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    Controlled synthesis of high-quality W-Y2O3 composite powder precursor by ascertaining the synthesis mechanism behind the wet chemical method
    Zhi Dong, Nan Liu, Weiqiang Hu, Zongqing Ma, Chong Li, Chenxi Liu, Qianying Guo, Yongchang Liu
    J. Mater. Sci. Technol., 2020, 36 (0): 118-127.  DOI: 10.1016/j.jmst.2019.05.067
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    As an emerging preparation technology, wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys, owing to its unique technical advantages. Ascertaining the synthesis mechanism behind wet chemical method is indispensable for controlled synthesis of high-quality W-Y2O3 composite powder precursor. The co-deposition mechanism of yttrium and tungsten component behind the wet chemical method of preparing yttrium-doped tungsten composite nanopowder was investigated systematically in this work. A series of co-deposited composite powders fabricated under different acidity conditions were used as research targets for investigating the effect of surface composition and structure on co-deposition efficiency. It was found that white tungstic acid has more W—OH bonds and much higher co-deposition efficiency with Y3+ ions than yellow tungstic acid. It is illustrated that the coordination reaction between W—OH bonds on tungstic acid particles and Y3+ ions brings the co-deposition of yttrium and tungsten component into being. Through displacing H+ ions in W—OH bonds, Y3+ ions can be adsorbed on the surface of or incorporated into tungstic acid particles in form of ligand. Consequently, to control and regulate Y2O3 content in powder precursor accurately, H+ ion concentration in wet chemical reaction should be in range of 0.55-2.82 mol L-1 to obtain white tungstic acid. Besides, H+ ion concentration also has prominent effect on the grain size and morphology of reduced powder precursor. The optimal value should be around 1.58 mol L-1, which can lead to minimum W grain size (about 17 nm) without bimodal structure. The chemical mechanism proposed in this work could produce great sense to preparation of high-quality precursor for sintering high-performance Y2O3 dispersion strengthened W based alloys. Our work may also shed light on the approach to exploit analogous synthesis mechanism in other alloy systems.

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    Structure and properties of nanoporous FePt fabricated by dealloying a melt-spun Fe60Pt20B20 alloy and subsequent annealing
    Dianguo Ma, Yingmin Wang, Yanhui Li, Umetsu Rie Y., Shuli Ou, Kunio Yubuta, Wei Zhang
    J. Mater. Sci. Technol., 2020, 36 (0): 128-133.  DOI: 10.1016/j.jmst.2019.05.066
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    A nanoporous FePt alloy has been fabricated by dealloying a melt-spun Fe60Pt20B20 alloy composed of nanoscale amorphous and face-centered-cubic FePt (fcc-FePt) phases in H2SO4 aqueous solution. The nanoporous alloy consists of single fcc-FePt phase with an Fe/Pt atomic ratio of about 55.3/44.7, and possesses a uniform interpenetrating ligament-channel structure with average ligament and pore sizes of 27 nm and 12 nm, respectively. The nanoporous fcc-FePt alloy shows soft magnetic characteristics with a saturation magnetization of 37.9 emu/g and better electrocatalytic activity for methanol oxidation than commercial Pt/C in acidic environment. The phase transformation from disordered fcc-FePt into ordered face-centered-tetragonal FePt (L10-FePt) in the nanoporous alloy has been realized after annealing at 823-943 K for 600 s. The volume fraction of the L10-FePt phase in the alloy increases with the rise of annealing temperature, which results in the enhancements of coercivity and saturation magnetization from 0.14 kOe and 38.5 emu/g to 8.42 kOe and 51.4 emu/g, respectively. The ligament size of the samples is increased after annealing.

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    Letter
    High entropy (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 with strong anisotropy in thermal expansion
    Heng Chen, Huimin Xiang, Fu-Zhi Dai, Jiachen Liu, Yanchun Zhou
    J. Mater. Sci. Technol., 2020, 36 (0): 134-139.  DOI: 10.1016/j.jmst.2019.07.022
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    A novel high entropy (HE) rare earth monosilicate (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 was synthesized by solid-state reaction method. X-ray diffraction and scanning electron microscopy analysis indicate that a single solid solution is formed with homogeneous distribution of rare-earth elements. HE (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 exhibits excellent phase stability and anisotropy in thermal expansion. The coefficients of thermal expansion (CTEs) in three crystallographic directions are: αa = (2.57 ± 0.07) ×10-6 K-1, αb = (8.07 ± 0.13) ×10-6 K-1, αc = (9.98 ± 0.10) ×10-6 K-1. The strong anisotropy in thermal expansion is favorable in minimizing the coating/substrate mismatch if preferred orientation of HE (Yb0.25Y0.25Lu0.25Er0.25)2SiO5 is controlled on either metal or ceramic substrate.

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    Research Article
    Controlling the strength of Zr (10 $\bar{1}$ 2) grain boundary by nonmetallic impurities doping: A DFT study
    Zhe Xue, Xinyu Zhang, Jiaqian Qin, Mingzhen Ma, Riping Liu
    J. Mater. Sci. Technol., 2020, 36 (0): 140-148.  DOI: 10.1016/j.jmst.2019.07.017
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    Impurity segregation even small amounts, can drastically change the cohesive properties of the grain boundaries (GB), eventually leading to intergranular embrittlement and failure of the materials, thereby effectively controlling the types and the concentrations of the impurity is very important. In this work, the nonmetallic impurities (C, H, O, N) segregation and their effects on the strength of Zr (10 $\bar{1}$ 2) GB were thoroughly investigated using first-principles calculations based on density functional theory. A comprehensive analysis of the interstitial configurations and the relative site energies indicating that C, N and O overwhelmingly prefer the octahedral sites, only H, prefers to reside in the tetrahedral sites. Moreover, the strengthening/embrittlement potency of impurity atoms on the GB was estimated using both the Rice-Wang model and first-principles tensile test calculations. The results show that all impurities, exhibit a strong segregation tendency near the GB region. The segregation of C, N and O has a remarkable strengthening effect on strength of the GB, whereas the presence of impurity H weaken the GB. Most importantly, the underlying mechanism of the strength change of the GBs due to the segregation of impurities was profoundly discussed by charge density and the bond lengths analyses, revealing that the strengthening effect especially for C-doped GB, mainly comes from an enhancement of the charge density across the GB plane. In the end, we expect that our results will be certainly useful for future theoretical and experimental investigations on Zr and its alloys.

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    Uniform texture in Al-Zn-Mg alloys using a coupled force field of electron wind and external load
    Hexiong Zhang, Xinfang Zhang
    J. Mater. Sci. Technol., 2020, 36 (0): 149-159.  DOI: 10.1016/j.jmst.2019.07.025
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    Cylindrical Al-Zn-Mg alloys were processed by electroplastic compression with forced air cooling. Compared to a simple compression process, an unequal intensity of {110} <1$\bar{1}$1> was obtained, and other textures were eliminated by electroplastic compression, that is, electroplastic compression can promote a uniform texture. The various textures formed in different regions along the radial direction under a simple compression process were illuminated by analyzing the relationship between the crystal rotation and stress state. Furthermore, the interaction between the electrons and dislocations was studied in electroplastic compression. The electrons enhanced {110} <1$\bar{1}$1> by promoting slipping of the dislocations when the Burgers vectors of the dislocations were parallel to the drift direction of the electrons. However, the electrons also inhibited crystal rotation by pinning the dislocations with the Burgers vectors perpendicular to the drift direction of the electrons. Therefore, textures other than {110} <1$\bar{1}$1> have difficulty forming under electroplastic compression. The effect of the current energy on the texture (enhancement or attenuation) was in accordance with the law of conservation. The results provided reasonable explanations for the test phenomena.

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    Accelerated flow softening and dynamic transformation of Ti-6Al-4V alloy in two-phase region during hot deformation via coarsening α grain
    Xiankun Ji, Baoqi Guo, Fulin Jiang, Hong Yu, Dingfa Fu, Jie Teng, Hui Zhang, John J.Jonas
    J. Mater. Sci. Technol., 2020, 36 (0): 160-166.  DOI: 10.1016/j.jmst.2019.08.005
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    The flow softening is an important phenomenon during hot deformation of metallic materials. In the present work, a more evident flow softening of Ti-6Al-4V alloy when deformed in two-phase region was observed in coarser α grain sample, which was attributed to an accelerated dynamic transformation from harder α phase into β phases. Notably, full β microstructure was observed in coarse grain samples at strain of 1.2, while retained α phase was observed in fine α grain specimens. In the views of thermodynamics and crystallographic analysis, the in-depth mechanisms of dynamic transformation were further investigated.

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    Anomalous crystal structure of γ″ phase in the Mg-RE-Zn(Ag) series alloys: Causality clarified by ab initio study
    Junyuan Bai, Xueyong Pang, Xiangying Meng, Hongbo Xie, Hucheng Pan, Yuping Ren, Min Jiang, Gaowu Qin
    J. Mater. Sci. Technol., 2020, 36 (0): 167-175.  DOI: 10.1016/j.jmst.2019.05.065
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    The crystal structure of the single-unit-cell thickness γ″ phase, as a key strengthening phase in Mg-RE-Zn (Ag) series alloys, has been extensively studied, and several structural models have been proposed in the past two decades. However, these reported models, and even the lattice constants at the same proposed structure, are scattered severely, which has led to considerable confusion and not available for further mechanical property simulation and prediction of Mg alloys containing this phase. In this study, by using first-principles calculations, the crystal structure of γ” phase is clarified, resolving the discrepancies among different experiments, and its intrinsic mechanical properties have also been studied for the first time. It is verified that the γ″ phase contains quasi-five atomic layers, instead of the previously reported tri-layer, and surprisingly, its crystal structure has many variants, which would change with the alloy composition. Besides, with the help of the simulated selected area electron diffraction (SAED) patterns, it is found that the atoms in the central layer remain partially ordered distribution, and this ordered extent primarily depends on the atomic ratio of RE: Zn(Ag) and the solute content in an alloy. That is, the ordered extent increases with decreasing the atomic ratio of RE:Zn(Ag) and/or increasing solute content of alloy, and vice versa. Ag and Zn dissolved in the γ″ phase would produce almost opposed mechanical anisotropy for the γ″ phase under the identical crystal structure, and the addition of Ag shows more efficient on increasing the shear modulus of γ″ phase.

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    Evolution of phase stresses in Al/SiCp composite during thermal cycling and compression test studied using diffraction and self-consistent models
    Przemysł Kot; aw, BaczmańAndrzej ski, GadalińElż ska; bieta, WrońSebastian ski, WrońMarcin ski, WróMirosł bel; aw, Gizo Bokuchava, ScheffzüChristian k, Krzysztof Wierzbanowski
    J. Mater. Sci. Technol., 2020, 36 (0): 176-189.  DOI: 10.1016/j.jmst.2019.03.046
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    In this work, the evolutions of stresses in both phases of the Al/SiCp composite subjected to thermal cycling during in situ compression test were measured using Time of Flight neutron diffraction. It was confirmed that inter-phase stresses in the studied composite can be caused by differences in the coefficient of thermal expansion for the reinforcement and matrix, leading to a different variation of phase volumes during sample heating or cooling. The results of the diffraction experiment during thermal cycling were well predicted by the Thermo-Mechanical Self-Consistent model. The experimental study of elastic-plastic deformation was carried out in situ on a unique diffractometer EPSILON-MDS (JINR in Dubna, Russia) with nine detector banks measuring interplanar spacings simultaneously in 9 orientations of scattering vector. For the first time, the performed analysis of experimental data allowed to study the evolution of full stress tensor in both phases of the composite and to consider the decomposition of this tensor into deviatoric and hydrostatic components. It was found that the novel Developed Thermo-Mechanical Self-Consistent model correctly predicted stress evolution during compressive loading, taking into account the relaxation of thermal origin hydrostatic stresses. The comparison of this model with experimental data at the macroscopic level and the level of phases showed that strengthening of the Al/SiCp composite is caused by stress transfer from the plastically deformed Al2124 matrix to the elastic SiCp reinforcement, while thermal stresses relaxation does not significantly affect the overall composite properties.

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    Invited Review
    Materials evolution of bone plates for internal fixation of bone fractures: A review
    Junlei Li, Ling Qin, Ke Yang, Zhijie Ma, Yongxuan Wang, Liangliang Cheng, Dewei Zhao
    J. Mater. Sci. Technol., 2020, 36 (0): 190-208.  DOI: 10.1016/j.jmst.2019.07.024
    Abstract   HTML   PDF

    Bone plates play a vital role in bone fracture healing by providing the necessary mechanical fixation for fracture fragments through modulating biomechanical microenvironment adjacent to the fracture site. Good treatment effect has been achieved for fixation of bone fracture with conventional bone plates, which are made of stainless steel or titanium alloy. However, several limitations still exist with traditional bone plates including loosening and stress shielding due to significant difference in modulus between metal material and bone tissue that impairs optimal fracture healing. Additionally, due to demographic changes and non-physiological loading, the population suffering from refractory fractures, such as osteoporosis fractures and comminuted fractures, is increasing, which imposes a big challenge to traditional bone plates developed for normal bone fracture repair. Therefore, optimal fracture treatment with adequate fixation implants in terms of materials and design relevant to special conditions is desirable. In this review, the complex physiological process of bone healing is introduced, followed by reviewing the development of implant design and biomaterials for bone plates. Finally, we discuss recent development of hybrid bone plates that contains bioactive elements or factors for fracture healing enhancement as a promising direction. This includes biodegradable Mg-based alloy used for designing bone screw-plates that has been proven to be beneficial for fracture healing, an innovative development that attracts more and more attention. This paper also indicates that the tantalum bone plates with porous structure are also emerging as a new fracture internal fixation implants. The reduction of the stress shielding is verified to be useful to accelerate bone fracture healing. Potential application of biodegradable metals may also avoid a second operation for implant removal. Further developments in biometals and their design for orthopedic bone plates are expected to improve the treatment of bone fracture, especially the refractory fractures.

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