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CN 21-1315/TG
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      20 September 2017, Volume 33 Issue 9 Previous Issue    Next Issue
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    Orginal Article
    Microstructure, texture and mechanical behavior characterization of hot forged cast ZK60 magnesium alloy
    Karparvarfard S.M.H., Shaha S.K., Behravesh S.B., Jahed H., Williams B.W.
    J. Mater. Sci. Technol., 2017, 33 (9): 907-918.  DOI: 10.1016/j.jmst.2017.04.004
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    Uniaxial tension and compression tests were conducted to investigate the quasi-static performance of ZK60 Mg alloy in cast, followed by forging at optimum temperature of 450℃ and a ram speed of 39 mm min-1. Microstructure and texture analysis showed that the as-cast alloy exhibited a dendritic structure with casting porosity and random texture. In contrast, the forged alloy exhibited a refined grain structure with a significant reduction in casting porosity, while the texture changed to sharp basal texture. Measured mechanical properties of the forged alloy showed that strength did not change, however, ductility improved by 75%. The analysis of the fracture surface of the forged alloy under tension revealed a ductile fracture with dimple morphology, while the as-cast alloy displayed a brittle fracture with open pores. This demonstrated that the reduction of casting defects and dendritic morphology, as well as the evolution of recrystallized grains, enhanced ductility, while partial dynamic recrystallization through the forging process resulted in only marginal modification of strength in the forged condition.

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    Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55Y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling
    Kwak T.Y., Kim W.J.
    J. Mater. Sci. Technol., 2017, 33 (9): 919-925.  DOI: 10.1016/j.jmst.2017.05.003
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    An ultrafine-grained (UFG) Mg-13Zn-1.55Y alloy (ZW132) with a high volume fraction (7.4%) of icosahedral phase (I-phase, Mg3Zn6Y) particles was prepared by applying high-ratio differential speed rolling (HRDSR) on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures (tensile elongations of 455% and 1021% 473 K- 10-3 s-1 and 523 K- 10-3 s-1, respectively). Compared with UFG Mg-9.25Zn-1.66Y alloy (ZW92) with a lower volume fraction of I-phase particles (4.1%), which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond 523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSR-processed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.

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    Effect of Nd on microstructure and mechanical properties of as-extruded Mg-Y-Zr-Nd alloy
    Xu Xiaoyang, Chen Xianhua, Du Weiwei, Geng Yuxiao, Pan Fusheng
    J. Mater. Sci. Technol., 2017, 33 (9): 926-934.  DOI: 10.1016/j.jmst.2017.04.011
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    The microstructure and mechanical properties of Mg-Y-Zr-xNd alloys with 0-2.63 wt% Nd were investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile testing test. Results indicated that more Mg24Y5 particles and Mg14Nd2Y (β) phases were dispersed in the matrix when Nd content increased from 0 wt% to 2.63 wt% in the extruded alloys. Consequently, the nucleation of dynamic recrystallization and the volume fraction of recrystallized grains were promoted obviously. The average grain size can be refined in the range of 4.6-1.3 μm after the addition of 2.63 wt% Nd. The tensile strength of extruded alloys increased with increasing Nd content, and elongation exhibited an opposite change tendency. The extruded alloy sheet with 1.01 wt% Nd demonstrates optimal combination of strength and plasticity, i.e., the ultimate tensile strength, yield strength, and elongation were 273 MPa, 214 MPa, and 24.2%, respectively. Variations in mechanical properties are discussed on the basis of microstructure observations.

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    Effect of homogenization on the microstructure and mechanical properties of the repetitive-upsetting processed AZ91D alloy
    Zhang Li, Wang Qudong, Liao Wenjun, Guo Wei, Ye Bing, Jiang Haiyan, Ding Wenjiang
    J. Mater. Sci. Technol., 2017, 33 (9): 935-940.  DOI: 10.1016/j.jmst.2017.01.015
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    The current research investigates the effect of homogenization on the microstructure and mechanical properties of the AZ91D alloy processed by repetitive upsetting (RU). Results show that during RU processing, the initial large Mg17Al12 particles in the as-cast specimen accelerate the dynamic recrystallization (DRX) due to the particle stimulating nucleation (PSN) mechanism. With the progress of RU, the inherent large strain breaks the large second phases into small fragments, which indicates the PSN gradually disappears, while the pinning effect becomes obvious. As for the homogenized specimen, a pre-heat treatment leads to the absence of Mg17Al12 particles but a uniform distribution of Al atoms in the Mg alloy. Though the subsequent RU promotes the precipitation of Mg17Al12 particles, the relatively small particle size and the uniform distribution are more favorable to act as obstacles for grain growth than contributors to PSN. Finally, a more homogeneous and refined microstructure is obtained in the specimen with prior homogenization than the as-cast one.

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    Enhanced Damping Capacities of Mg-Ce Alloy by the Special Microstructure with Parallel Second Phase
    Wu Zhongshan, Wang Jingfeng, Wang Haibo, Ma She, Huang Song, Li Shun, Pan Fusheng
    J. Mater. Sci. Technol., 2017, 33 (9): 941-946.  DOI: 10.1016/j.jmst.2016.06.027
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    Microstructure evolution and damping capacities of Mg-Ce binary alloys with three different Ce contents (0.5, 1, or 2 wt%) have been systematically investigated in this work. Numerous fine parallel second phases in Mg-2Ce alloy are obtained, as well as a large number of dislocations around them, but few dislocations appear around the reticular second phase in the Mg-1Ce alloy. Among the three alloys, two internal friction peaks (P1 and P2) are detected at about 78 and 167°C in both the Mg-0.5Ce and Mg-1Ce alloys. In addition, the alloy with special parallel second phase structure exhibits excellent damping capacity in both strain amplitude and temperature-dependent regions. These results may be ascribed to the stress concentration and the formation of abundant parallel and uniform dislocation configurations in the α-Mg matrix without the influence of crystal orientation. The obtained results may provide a novel idea to prepare high-damping magnesium alloys by tailoring their microstructure.

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    Microstructure and mechanical properties at elevated temperature of Mg-Al-Ni alloys prepared through powder metallurgy
    Hou Legan, Li Bingcheng, Wu Ruizhi, Cui Lin, Ji Peng, Long Ruiying, Zhang Jinghua, Li Xinlin, Dong Anping, Sun Baode
    J. Mater. Sci. Technol., 2017, 33 (9): 947-953.  DOI: 10.1016/j.jmst.2017.02.002
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    Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al3Ni2 particles and fine AlNinano-particles exist in the Mg-Al-Ni alloys. The strength at 150℃ is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of 234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al3Ni2 and AlNi in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of AlNi phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.

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    Pitting corrosion of a Rare Earth Mg alloy GW93
    Song Yingwei, Shan Dayong, Han En-Hou
    J. Mater. Sci. Technol., 2017, 33 (9): 954-960.  DOI: 10.1016/j.jmst.2017.01.014
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    Pitting corrosion of magnesium (Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix, while the second phases in Rare earth (RE) Mg alloy GW93 are more active than Mg matrix. As a result, the pitting corrosion mechanism of Mg alloy GW93 is different from the traditional ones. This paper aims to clarify the pitting corrosion mechanism of Mg alloy GW93 through the studies of Volta potential by Scanning Kelvin Probe Force Microscopy (SKPFM), corrosion morphology by Scanning Electron Microscope (SEM), and corrosion resistance by electrochemical tests. Results reveal that the pitting corrosion of GW93 includes three stages, first, dissolution of the second phases, followed by corrosion of Mg matrix adjacent to the dissolved second phases, and finally, propagation of corrosion pits along the depth direction of the dissolved second phases. Anodic second phases and enrichment of Cl- in the thick corrosion product films dominate the propagation of pitting corrosion.

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    Tailoring the microstructure and mechanical properties of the final Al-Mn foils by different intermediate annealing process
    Huang Li, Huang Guangjie, Xin Yunchang, Cao Lingfei, Wu Xiaodong, Jia Zhihong, Li Qilei, Liu Qing
    J. Mater. Sci. Technol., 2017, 33 (9): 961-970.  DOI: 10.1016/j.jmst.2017.03.009
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    In this work, two different intermediate annealing processes, single-step annealing (SSA, 530℃/15 h) and two-step annealing (TSA, 450℃/5 h + 530℃/15 h), were used to tailor microstructure before cold-rolling and annealing of the final twin-roll cast Al-Mnfoils. The recrystallization behavior and mechanical properties during annealing of severely cold-rolled foils were systematically studied. Our results show that discontinuous recrystallization occurs in SSA-foils during annealing at 150-310℃, in contrast with continuous recrystallization in TSA-foils. The continuous recrystallization develops much finer grains (~1.35 μm) in the TSA-foils than those by discontinuous recrystallization in the SSA-foils (~14.7 μm). The texture components in cold-rolled TSA-foils hardly change (retained rolling-textures) after continuous recrystallization, while those in the cold-rolled SSA-foils mainly transform into a strong cube component {001} 〈100〉 after discontinuous recrystallization. Finally, a maximized elongation to fracture of ~23.9% was achieved in the TSA-foil, much higher than that of the SSA-counterparts, ~8.3%. The relationships between the microstructure and mechanical properties were discussed.

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    New insights into the effect of Tris-HCl and Tris on corrosion of magnesium alloy in presence of bicarbonate, sulfate, hydrogen phosphate and dihydrogen phosphate ions
    Cui Lan-Yue, Hu Yan, Zeng Rong-Chang, Yang Yong-Xin, Sun Dan-Dan, Li Shuo-Qi, Zhang Fen, Han En-Hou
    J. Mater. Sci. Technol., 2017, 33 (9): 971-988.  DOI: 10.1016/j.jmst.2017.01.005
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    In vitro degradation is an important approach to screening appropriate biomedical magnesium (Mg) alloys at low cost. However, corrosion products deposited on Mg alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg alloys. Understanding the degradation behavior of Mg alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg alloy AZ31 in the presence of various anions of simulated body fluids via hydrogen evolution, pH value and electrochemical tests. The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the AZ31 alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution pH value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO3-, SO42-, HPO42- and H2PO4- ions during the corrosion of the AZ31 alloy due to its lower buffering pH value (x.x). Thus, both the hydrogen evolution rate and corrosion current density of the alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.

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    Global and local constitutive behaviors of friction stir welded AA2024 joints
    Niu Pengliang, Li Wenya, Zhang Zhihan, Yang Xiawei
    J. Mater. Sci. Technol., 2017, 33 (9): 987-990.  DOI: 10.1016/j.jmst.2017.02.010
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    In this study, the global and local tensile properties of friction stir welded AA2024 joints were measured with the aid of digital image correlation (DIC) method. A novel model was proposed to describe the global and local constitutive behavior of the joints based on DIC data. Different from conventional division of the zones across the joints, a new reasonable division was proposed, i.e. four zones including central low hardness zone (CLHZ), first heat affected zone (HAZ-I) close to TMAZ, second heat affected zone (HAZ-II) close to base metal (BM) and BM in term of the characteristic distribution of hardness. Results reveal that local true stress-true strain curves are different in each zone of interest. Plastic deformation of the joints is concentrated in CLHZ, where the lowest yield stress and the largest strain appear. Therefore, strain localization and necking occur here in a sequence. In addition, the global true stress-true strain curves and yield stresses at various ratios of the width of CLHZ zone to the gauge length are accurately predicted using the proposed constitutive model of the joints.

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    Characterizing and modeling the precipitation of Mg-rich phases in Al 5xxx alloys aged at low temperatures
    Yi Gaosong, Zeng Weizhi, D. Poplawsky Jonathan, A. Cullen David, Wang Zhifen, L. Free Michael
    J. Mater. Sci. Technol., 2017, 33 (9): 991-1003.  DOI: 10.1016/j.jmst.2017.02.001
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    Al 5083 alloys (5.25 at.% Mg) of different tempers (H131 and H116) were aged at low temperatures (50 and 70℃) for 41 months. Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and atom probe tomography (APT) were applied to characterize precipitates formed in the sensitized samples. Experimental results revealed that the size of Mg-rich precipitates increased with aging time at 70℃ for both alloys. APT results showed that Mg-rich precipitates of different Mg concentrations and morphologies formed in Al matrix and on the interface of Al matrix/pre-existing particles. In addition, a model based on local equilibrium of chemical potential and multi-class precipitates number evolution was adopted to predict the multiphase precipitation process in the Al-Mg binary system. The overall trend of precipitate radius and number density predicted by the model matched well with the experimental results. Moreover, modeling results revealed that nucleation and coarsening occurred faster in Al 5083 H131 than in Al 5083 H116 when aged at same temperature. The high density of dislocations and the pipe diffusion mechanism of dislocations can be used to explain such behavior.

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    Friction stir welding of carbon nanotubes reinforced Al-Cu-Mg alloy composite plates
    Zhao Ke, Liu Zhenyu, Xiao Bolyu, Ma Zongyi
    J. Mater. Sci. Technol., 2017, 33 (9): 1004-1008.  DOI: 10.1016/j.jmst.2017.01.033
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    Carbon nanotubes (CNTs) reinforced Al-Cu-Mg composite plates of 2.2 mm in thickness after extrusion and T4 treatment were joined by friction stir welding (FSW) and the joint efficiency reaches 87%. There was no precipitate in both heat-affected zone (HAZ) and nugget zone (NZ) as a medium rotation rate of 800 rpm and a relative high travel speed of 100 mm min-1 were used. In the NZ, FSW disarranged the alignment of CNTs to random orientation and dispersed CNT uniformly. The orientation of CNTs perpendicular to the tensile direction and the possible dissolution of solute clusters made the HAZ become the weakest zone in the joint leading to the failure in the HAZ.

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    Enhanced Mechanical Properties of Friction Stir Welded 5083Al-H19 Joints with Additional Water Cooling
    Wang B.B., Chen F.F., Liu F., Wang W.G., Xue P., Ma Z.Y.
    J. Mater. Sci. Technol., 2017, 33 (9): 1009-1014.  DOI: 10.1016/j.jmst.2017.01.016
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    3-mm-thick 5083Al-H19 rolled plates were friction stir welded (FSW) at tool rotation rates of 800 and 200 rpm with and without additional water cooling. With decreasing the rotation rate and applying water cooling, softening in the FSW joint was significantly reduced. At a low rotation rate of 200 rpm with additional water cooling, almost no obvious softening was observed in the FSW joint, and therefore a FSW 5083Al-H19 joint with nearly equal strength to the base material (BM) was obtained. Furthermore, the grains in the nugget zone were considerably refined with reducing the heat input and ultrafine equiaxed grains of about 800 nm were obtained in the lowest heat input condition. This work provides an effective method to achieve high property FSW joints of precipitate-hardened and work-hardened Al alloys.

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    Effect of Sc and Zr additions on microstructures and corrosion behavior of Al-Cu-Mg-Sc-Zr alloys
    Sun Fangfang, Liu Nash Guiru, Li Qunying, Liu Enzuo, He Chunnain, Shi Chunsheng, Zhao Naiqin
    J. Mater. Sci. Technol., 2017, 33 (9): 1015-1022.  DOI: 10.1016/j.jmst.2016.12.003
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    The effects of adding the alloy element Sc to Al alloys on strengthening, recrystallization and modification of the grain microstructure have been investigated. The combination of Sc and Zr alloying not only produces a remarkable synergistic effect of inhibition of recrystallization and refinement of grain size but also substantially reduce the amount of high-cost additional Sc. In this work, the microstructures and corrosion behavior of a new type of Al-Cu-Mg-Sc-Zr alloy with Sc/Zr ratio of 1/2 were investigated. The experimental results showed that the Sc and Zr additions to Al-Cu-Mg alloy could strongly inhibit recrystallization, refine grain size, impede the segregation of Cu element along the grain boundary and increase the spacing of grain boundary precipitates. In addition, adding Sc and Zr to Al-Cu-Mg alloy effectively restricts the corrosion mechanism conversion associated with Al2CuMg particles, which resulted in the change of the cross-section morphology of inter-granular corrosion from an undercutting to an elliptical shape. The susceptibility to inter-granular corrosion was significantly decreased with increasing Sc and Zr additions to the Al-Cu-Mg alloy. The relationships between microstructures evolution and inter-granular corrosion mechanism of Al-Cu-Mg-Sc-Zr alloys were also discussed.

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    Effects of SiC Nanoparticle Content on the Microstructure and Tensile Mechanical Properties of Ultrafine Grained AA6063-SiCnp Nanocomposites Fabricated by Powder Metallurgy
    Yao X., Zhang Z., Zheng Y.F., Kong C., Quadir M.Z., Liang J.M., Chen Y.H., Munroe P., Zhang D.L.
    J. Mater. Sci. Technol., 2017, 33 (9): 1023-1030.  DOI: 10.1016/j.jmst.2016.09.022
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    Ultrafine grained AA6063-SiCnp nanocomposites with 1, 5 and 10 vol.%SiCnp have been fabricated by a novel powder metallurgy process. This process combines high energy ball milling of a mixture of 6063 alloy granules made from machining chips and SiC nanoparticles and thermomechanical powder consolidation by spark plasma sintering and hot extrusion. The microstructure and tensile mechanical properties of the samples were investigated in detail. Increasing the SiC nanoparticle content from 1 to 10 vol.%, the yield strength and ultimate tensile strength increased from 296 and 343 MPa to 545 and 603 MPa respectively, and the elongation to fracture decreased from 10.0%, to 2.3%. As expected, a higher SiC nanoparticle content generates a stronger inhibiting effect to grain growth during the thermomechanical powder consolidation process. Analysis of the contributions of various strengthening mechanisms shows that a higher SiC nanoparticle content leads to a higher contribution from nanoparticle strengthening, but grain boundary strengthening still makes the largest contribution to the strength of the nanocomposite. When the SiC nanoparticle content increased to 10 vol.%, the failure of the nanocomposite was initiated at weakly-bonded interparticle boundaries (IPBs), indicating that with a high flow stress during tensile deformation, the failure of the material is more sensitive to the presence of weakly-bonded IPBs.

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    Effect of ECAP consolidation temperature on the microstructure and mechanical properties of Al-Cu-Ti metallic glass reinforced aluminum matrix composite
    Rezaei M.R., Shabestari S.G., Razavi S.H.
    J. Mater. Sci. Technol., 2017, 33 (9): 1031-1038.  DOI: 10.1016/j.jmst.2016.10.013
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    Al65Cu20Ti15 metallic glass (AMG) reinforced Al matrix composites were consolidated by equal channel angular pressing (ECAP) process. The effects of ECAP consolidation temperature ranging from room temperature to just below the first crystallization temperature of metallic glass on the consolidation of composites were investigated in terms of the relative densities, structural evolutions and mechanical properties of composites. Some intermetallic compounds included Al5CuTi2, Al3Ti and Al4Cu9 precipitated from metallic glass particles at consolidation temperature of 300℃. Consolidation temperature did not affect the matrix grains size of the composite. Quantitative analysis revealed that the distribution of reinforcing particles was considerably dependent on consolidation temperature. Density of the composite was increased by increasing the consolidation temperature to 250℃. The composite consolidated at 250℃ through ECAP process, exhibited the best combination of yield strength and ductility of 184 MPa and 48%, respectively.

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    Microstructural Evolution and Service Performance of Cold-drawn Pure Aluminum Conductor Wires
    Luo X.M., Song Z.M., Li M.L., Wang Q., Zhang G.P.
    J. Mater. Sci. Technol., 2017, 33 (9): 1039-1043.  DOI: 10.1016/j.jmst.2016.11.018
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    Microstructures and service performance (mechanical and electrical properties) of the commercially pure Al conductor wires subjected to different cold drawing strains were investigated. The results show that the microstructures of the cold-drawn Al wires along the radial direction were inhomogeneous, i.e. the texture in the center region was strong <111> and weak <001> components, while that in the surface region shifted from the initial cubic texture to a <112> component and finally developed into a strong <111> component. The volume fraction of the high angle grain boundaries in the surface region was higher than that in the center region. The cold-drawing process greatly enhanced the yield strength of the pure Al wires while retained the acceptable electrical resistivity. The strengthening mechanism and the variation of electrical conductivity of the cold-drawn Al wires are discussed through correlating with microstructure evolution.

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    Electronic structure and mechanical properties of layered compound YB2C2: A promising precursor for making two dimensional (2D) B2C2 nets
    Zhou Yanchun, Xiang Huimin, Wang Xiaohui, Sun Wei, Dai Fu-Zhi, Feng Zhihai
    J. Mater. Sci. Technol., 2017, 33 (9): 1044-1054.  DOI: 10.1016/j.jmst.2016.09.028
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    Layered compounds play pivotal roles as precursors for producing 2D materials through mechanical exfoliation (micro-mechanical cleavage) or chemical approaches. Therefore, searching for layered compounds with sharp anisotropic chemical bonding and properties becomes emergent. In this work, the stability, electronic structure, elastic properties, and lattice dynamics of YB2C2 were investigated. Strong anisotropy in elastic properties is revealed, i.e., high Young's modulus in a-b plane but low Young's modulus in c direction. The maximum to minimum Young's modulus ratio is 2.41 and 2.45 for YB2C2 with P42/mmc and P4/mbm symmetry, respectively. The most likely systems for shear sliding or micro-delaminating are (001)[100] and (001)[010]. The anisotropic elastic properties are underpinned by the anisotropic chemical bonding, i.e., strong bonding within the B2C2 nets and weak bonding between Y atom layers and B2C2 nets. YB2C2 is electrically conductive and the contributions to the electrical conductivity are from delocalized Y 4deg as well as B 2pz and C 2pz electrons. The layered crystal structure, sharp anisotropic mechanical properties, and metallic conductivity endorse YB2C2 promising as a precursor for new 2D B2C2 nets.

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    Surface Microstructure and High Temperature Oxidation Resistance of Thermal Sprayed NiCoCrAlY Bond-Coat Modified by Cathode Plasma Electrolysis
    Deng Shunjie, Wang Peng, He Yedong, Zhang Jin
    J. Mater. Sci. Technol., 2017, 33 (9): 1055-1060.  DOI: 10.1016/j.jmst.2016.09.005
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    The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis (CPE). After modification, a re-melted layer without obvious pores and oxide stringers is formed, the gain size of re-melted layer is approximately 80-120 nm. It is shown, from cyclic oxidation at 1100 °C, that a thin oxide scale mainly composed of α-Al2O3 has been formed on the modified bond-coat and the oxidation resistance of the modified bond-coat has been significantly improved. Such beneficial result can be attributed to following effects: during CPE process, the plasma discharges with high temperature take place on the bond-coat surface. With plasma discharge treatment, the surface is melted and quickly re-solidified, the grain size decreases, and the pores and oxide stringers disappear. During cyclic oxidation, owing to the above modification of surface properties, the critical content of Al for selective oxidation is significantly decreased. Therefore, a continuous Al2O3 scale is formed.

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    High pressure floating-zone growth and property characterization of Cr-doped hexagonal YMnO3 crystals
    Wan Feng, Bai Xiaojun, Song Kaikai, Zheng Jianbang, Lin Xin, Cao Chongde
    J. Mater. Sci. Technol., 2017, 33 (9): 1061-1066.  DOI: 10.1016/j.jmst.2017.04.014
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    Large crystal growth of Cr-doped h-YMnO3 has been investigated by using a high pressure optical floating-zone method. The size of the grown crystals is typically 60-70 mm in length and 4-5 mm in diameter. The structure of the grown crystals is analyzed by powder X-ray diffraction and scanning electron microscopy. The defects in the as-grown crystals, including low-angle grain boundary and inclusions are studied. An off-stoichiometric phenomenon is found with a slight Cr deficiency in different parts. The relationship between defects and growth conditions during crystal growth is also discussed. The magnetic properties show spin-glass phase features with weak ferromagnetic behavior below 30 K.

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