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 July 2018, Volume 34 Issue 7 Previous Issue    Next Issue
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    Orginal Article
    Insight from in situ microscopy into which precipitate morphology can enable high strength in magnesium alloys
    Bo-Yu Liu, Nan Yang, Jian Wang, Matthew Barnett, Yun-Chang Xin, Di Wu, Ren-Long Xin, Bin Li, R.Lakshmi Narayan, Jian-Feng Nie, Ju Li, Evan Ma, Zhi-Wei Shan
    J. Mater. Sci. Technol., 2018, 34 (7): 1061-1066.  DOI: 10.1016/j.jmst.2018.01.017
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    Magnesium alloys, while boasting light weight, suffer from a major drawback in their relatively low strength. Identifying the microstructural features that are most effective in strengthening is therefore a pressing challenge. Deformation twinning often mediates plastic yielding in magnesium alloys. Unfortunately, due to the complexity involved in the twinning mechanism and twin-precipitate interactions, the optimal precipitate morphology that can best impede twinning has yet to be singled out. Based on the understanding of twinning mechanism in magnesium alloys, here we propose that the lamellar precipitates or the network of plate-shaped precipitates are most effective in suppressing deformation twinning. This has been verified through quantitative in situ tests inside a transmission electron microscope on a series of magnesium alloys containing precipitates with different morphology. The insight gained is expected to have general implications for strengthening strategies and alloy design.

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    Microstructural evolution and mechanical properties of Mg-9.8Gd-2.7Y-0.4Zr alloy produced by repetitive upsetting
    H. Zhou, H.Y. Ning, X.L. Ma, D.D. Yin, L.R. Xiao, X.C. Sha, Y.D. Yu, Q.D. Wang, Y.S. Li
    J. Mater. Sci. Technol., 2018, 34 (7): 1067-1075.  DOI: 10.1016/j.jmst.2018.01.009
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    A newly developed severe plastic deformation (SPD) technique, i.e. repetitive upsetting (RU), is employed to improve the strength and ductility of a Mg-Gd-Y-Zr alloy. During the RU processing, dynamic recrystallization occurs in the Mg alloy, which leads to a significant grain refinement from 11.2 μm to 2.8 μm. The yield strength (YS), ultimate tensile strength (UTS) and elongation increase simultaneously with increasing RU passes. The microstructural evolution is affected by processing temperatures. Dynamic recrystallization prevails at low temperatures, while dynamic recovery is the main effect factor at high temperatures. Texture characteristics gradually become random during multiple passes of RU processing, which reduces the tension-compression asymmetry of the Mg-Gd-Y-Zr alloy.

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    Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment
    Guoqiang Li, Jinghuai Zhang, Ruizhi Wu, Yan Feng, Shujuan Liu, Xiaojun Wang, Yufeng Jiao, Qiang Yang, Jian Meng
    J. Mater. Sci. Technol., 2018, 34 (7): 1076-1084.  DOI: 10.1016/j.jmst.2017.12.011
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    A new cast Mg-2Gd-2Nd-2Y-1Ho-1Er-0.5Zn-0.4Zr (wt%) alloy was prepared by direct-chill semi-continuous casting technology. The microstructure, mechanical properties and thermal conductivity of the alloy in as-cast, solid-solution treated and especially peak-aged conditions were investigated. The as-cast alloy mainly consists of α-Mg matrix, (Mg, Zn)3 RE phase and basal plane stacking faults. After proper solid-solution treatment, the microstructure becomes almost Mg-based single phase solid solution except just very few RE-riched particles. The as-cast and solid-solution treated alloys exhibit moderate tensile properties and thermal conductivity. It is noteworthy that the Mg alloy with 8 wt% multiple RE exhibits remarkable age-hardening response (ΔHV = 35.7), which demonstrates that the multiple RE (RE = Gd, Nd, Y, Ho, Er) alloying instead of single Gd can effectively improve the age-hardening response. The peak-aged alloy has a relatively good combination of high strength/hardness (UTS (ultimate tensile strength) > 300 MPa; TYS (tensile yield strength) > 210 MPa; 115.3 HV), proper ductility (ε ≈ 6%) and moderate thermal conductivity (52.5 W/(m K)). The relative mechanisms mainly involving aging precipitation of β¢ and β′′ phases were discussed. The results provide a basis for development of high performance cast Mg alloys.

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    Facile one-step synthesis of Cu2O@Cu sub-microspheres composites as anode materials for lithium ion batteries
    Huijie Zhou, Hongbin Zhao, Xuan Zhang, Hongwei Cheng, Xionggang Lu, Qian Xu
    J. Mater. Sci. Technol., 2018, 34 (7): 1085-1090.  DOI: 10.1016/j.jmst.2017.12.010
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    Cu2O@Cu sub-microspheres composites with a narrow particle size distribution from 300 to 500 nm was successfully fabricated by one-step synthesis through the direct thermal decomposition of copper nitrate (Cu(NO3)2) in octadecylamine (ODA) solvent. As anode materials for lithium ion batteries, the Cu2O@Cu composites obviously possess high specific capacity, excellent cyclic stability and rate capability. The coulombic efficiency is about 84% in the 1 st cycle and increases significantly up to 97.8% during successive cycles at various current densities. Even under a high current density of 500 mA g-1, the discharge capacity of Cu2O@Cu composites remains up to 200 mAh g-1. The excellent electrochemical properties are ascribed to the synergistic effect between high electronic conductivity and volume-buffering capacity of metallic copper composited with Cu2O.

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    Grain refinement and orientation of AZ31B magnesium alloy in hot flow forming under different thickness reductions
    Yalian Zhang, Fenghua Wang, Jie Dong, Li Jin, Conghui Liu, Wenjiang Ding
    J. Mater. Sci. Technol., 2018, 34 (7): 1091-1102.  DOI: 10.1016/j.jmst.2017.12.007
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    An analysis of the hot flow forming of Mg-3.0Al-1.0Zn-0.3Mn (AZ31B) alloy was conducted by experiments and numerical simulations. The effects of different thickness reductions on the microstructure and mechanical properties were investigated at a temperature of 693 K, a spindle speed of 800 rev/min and a feed ratio of 0.1 mm/rev. Thickness reductions have great influence on the uniformity of microstructure along the radial direction (RD) and the grain sizes become refined and uniform when the thickness reduction reaches 45%. The c-axes of most grains are approximately parallel to the RD, with a slight inclination towards the axial direction (AD). The best mechanical properties with UTS of 280 MPa and YS of 175 MPa near the outer surface while 266 MPa and 153 MPa near the inner surface have been achieved due to grain refinement and texture. Moreover, the material flow behavior and stress/strain distributions for single-pass reductions were studied using the ABAQUS/Explicit software. The calculated results indicate that the materials mainly suffer from triaxial compressive stresses and undergo compressive plastic strain in RD and tensile strains in other directions. The higher stress and strain rate near the outer surface lead to more refined grains than that of other regions along the RD, whereas the orientation of the maximum principal compressive stress leads to a discrepancy of the grain orientations in RD.

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    High-performance asymmetric supercapacitors based on reduced graphene oxide/polyaniline composite electrodes with sandwich-like structure
    Jun Ma, Shaochun Tang, Junaid Ali Syed, Dongyun Su, Xiangkang Meng
    J. Mater. Sci. Technol., 2018, 34 (7): 1103-1109.  DOI: 10.1016/j.jmst.2017.12.006
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    The sandwich-like structure of reduced graphene oxide/polyaniline (RGO/PANI) hybrid electrode was prepared by electrochemical deposition. Both the voltage windows and electrolytes for electrochemical deposition of PANI and RGO were optimized. In the composites, PANI nanofibers were anchored on the surface of the RGO sheets, which avoids the re-stacking of neighboring sheets. The RGO/PANI composite electrode shows a high specific capacitance of 466 F/g at 2 mA/cm2 than that of previously reported RGO/PANI composites. Asymmetric flexible supercapacitors applying RGO/PANI as positive electrode and carbon fiber cloth as negative electrode can be cycled reversibly in the high-voltage region of 0-1.6 V and displays intriguing performance with a maximum specific capacitance of 35.5 mF cm-2. Also, it delivers a high energy density of 45.5 mW h cm-2 at power density of 1250 mW cm-2. Furthermore, the asymmetric device exhibits an excellent long cycle life with 97.6% initial capacitance retention after 5000 cycles. Such composite electrode has a great potential for applications in flexible electronics, roll-up display, and wearable devices.

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    Strengthening mechanisms in magnesium alloys containing ternary I, W and LPSO phases
    N. Tahreen, D.F. Zhang, F.S. Pan, X.Q. Jiang, D.Y. Li, D.L. Chen
    J. Mater. Sci. Technol., 2018, 34 (7): 1110-1118.  DOI: 10.1016/j.jmst.2017.12.005
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    This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium (Y) element. The addition of Y resulted in the formation of ternary I (Mg3YZn6), W (Mg3Y2Zn3) and LPSO (Mg12YZn) phases which subsequently reinforced alloys ZM31 + 0.3Y, ZM31 + 3.2Y and ZM31 + 6Y, where the value denoted the amount of Y element (in wt%). Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion (CTE), which was derived to be 1.38 × 10-5 K-1 and 2.35 × 10-5 K-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and CTE mismatch were the predominant strengthening mechanisms in the ZM31 + 0.3Y and ZM31 + 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 + 6Y alloy.

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    Coatings on Mg alloys and their mechanical properties: A review
    Toko Tokunaga, Munekazu Ohno, Kiyotaka Matsuura
    J. Mater. Sci. Technol., 2018, 34 (7): 1119-1126.  DOI: 10.1016/j.jmst.2017.12.004
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    Poor corrosion resistance is a serious drawback of Mg alloys, restricting their practical applications. Coating is one of the effective techniques for improvement in the poor corrosion resistance. In this paper, the coating processes for Mg alloys so far developed are reviewed. Among several processes, the coating processes based on mechanical energy, including metal forming, are attractive because the corrosion resistance and formability of Mg alloys are simultaneously improved.

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    Heat treatment enhancing the compressive fatigue properties of open-cellular Ti-6Al-4V alloy prototypes fabricated by electron beam melting
    Wei Yuan, Wentao Hou, Shujun Li, Yulin Hao, Rui Yang, Lai-Chang Zhang, Yue Zhu
    J. Mater. Sci. Technol., 2018, 34 (7): 1127-1131.  DOI: 10.1016/j.jmst.2017.12.003
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    : In this work, we report the effect of annealing in α+β phase field on the fatigue properties of Ti-6Al-4V alloy meshes fabricated by electron beam melting. The results show that annealing at high temperature near the phase boundary enhances the ductility of the brittle mesh struts due to the formation of coarse α lamellas with a large thickness/length ratio. Accordingly, the fatigue endurance ratio of the studied meshes increases to up to -0.6, which is much superior to that of the as-fabricated counterparts and comparable to those of dense materials.

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    Solute-homogenization model and its experimental verification in Mg-Gd-based alloys
    Shengnan Qian, Chuang Dong, Tianyu Liu, Ying Qin, Qing Wang, Yujuan Wu, Lidong Gu, Jianxin Zou, Xiangwen Heng, Liming Peng, Xiaoqin Zeng
    J. Mater. Sci. Technol., 2018, 34 (7): 1132-1141.  DOI: 10.1016/j.jmst.2017.11.053
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    Composition homogenization in solid solution is important for industrial alloys. In the present work, a solute homogenization model is proposed based on the chemical short-range-order tendency in Mg-Gd-based alloys. After a calculation using the cluster-plus-glue-atom model, the stable Mg-Gd structural unit is derived, [Gd-Mg12]Mg6, where one solute Gd is nearest-neighbored with twelve Mg atoms to form the characteristic hcp cluster [Gd-Mg12] and this cluster is matched with six Mg glue atoms. Such a local unit is then mixed with [Mg-Mg12]Mg3, the stable unit for pure Mg. Assuming that the Gd-containing units are arranged in fcc- or bcc-like lattice points and the Mg units in their octahedral interstices, three proportions between the two units are obtained, 1:1, 2:3, and 1:3, which constitute three solute homogenization modes. The prevailing Mg-Gd-based alloys are consequently classified into three groups, respectively exemplified by GW103 K (Mg-10Gd-3Y-0.4Zr, wt%), GW83 K (Mg-8Gd-3Y-0.4Zr), and GW63 K (Mg-6Gd-3Y-0.4Zr). Mg-Gd-Y-Zr alloys were designed following the model (where Y and Zr were also added in substitution for Gd) and prepared by permanent-mould casting. According to their mechanical properties, the 1:3 alloy (Mg-5.9Gd-1.6Y-0.4Zr) shows the best comprehensive properties (ultimate tensile strength 305 MPa, yield strength 186 MPa, elongation 9.0%) in solution plus ageing state.

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    Effect of cooling rates on the dendritic morphology transition of Mg-6Gd alloy by in situ X-ray radiography
    Yongbiao Wang, Liming Peng, Yanzhou Ji, Xiaoxing Cheng, Cunlong Wang, Yujuan Wu, Yanan Fu, Long-Qing Chen
    J. Mater. Sci. Technol., 2018, 34 (7): 1142-1148.  DOI: 10.1016/j.jmst.2017.11.047
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    The effect of cooling rate on the transition of dendrite morphology of a Mg-6Gd (wt%) alloy was semiquantitatively analyzed under a constant temperature gradient by using synchrotron X-ray radiographic technique. Results show that equiaxed dendrites, including exotic ‘butterfly-shaped’ dendrite morphology, dominate at high cooling rate (>1 K/s). When the cooling rate decreases in the range of 0.5-1 K/s, the equiaxed-to-columnar transition takes place, and solute segregates at the center of two long dendrite arms (LDA) of the ‘butterfly-shaped’ dendrite. When the cooling rate is lower than 0.3 K/s, directional solidification occurs and the columnar dendritic growth direction gradually rotates from the crystalline axis to the thermal gradient direction with an increase in cooling rate. Meanwhile, interface moves faster but the dendrite arm spacing decreases. Floating, collision and rotation of dendrites under convection were also studied in this work.

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    Partial melting behavior and thixoforming properties of extruded magnesium alloy AZ91 with and without addition of SiC particles with a volume fraction of 15%
    Yu-Shi Yi, Yi Meng, Dan-Qing Li, Sumio Sugiyama, Jun Yanagimoto
    J. Mater. Sci. Technol., 2018, 34 (7): 1149-1161.  DOI: 10.1016/j.jmst.2017.11.044
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    A series of reheating-isothermal holding experiments and compression tests were conducted on pristine magnesium alloy AZ91 extruded by equal channel angular extrusion (ECAE) and SiC particles (a volume fraction of 15%) reinforced AZ91 composite (AZ91-SiCp) by regular extrusion. Dissolution of eutectic compounds and partial melting of the α-Mg matrix occurred during the reheating of these materials. Spherical semisolid slurries of these materials were obtained when the reheating temperature and isothermal holding time were 550 °C and 20 s, respectively. The presence of SiCp in AZ91-SiCp not only caused lower liquid fractions of semisolid slurries but also resulted in higher values of flow stress during semisolid compression tests. Both AZ91 alloy and AZ91-SiCp composite exhibited better thixoforming properties at high temperatures. Segregation of SiCp did not occur during thixoforming of AZ91-SiCp composite after an isothermal holding at semisolid temperatures for 20 s.

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    Relationship between dealloying conditions and coarsening behaviors of nanoporous copper fabricated by dealloying Cu-Ce metallic glasses
    Ning Wang, Ye Pan, Shikai Wu
    J. Mater. Sci. Technol., 2018, 34 (7): 1162-1171.  DOI: 10.1016/j.jmst.2017.11.043
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    Monolithic nanoporous copper (NPC) with tunable ligament size (107-438 nm) was synthesized by dealloying a new Cu-Ce binary glassy precursor in dilute H2SO4 aqueous solution. The effects of the dealloying conditions on the morphologies of NPC were evaluated comprehensively. The results show that the ligaments of NPC can significantly coarsen with the increase of acid concentration, elevation of reaction temperature or prolongation of immersion time. These coarsening behaviors can be well described by a diffusion based growth kinetic model. Moreover, the surface diffusivity and activation energy for diffusion of Cu atoms were also estimated to investigate the formation mechanism of NPC, which is mainly governed by dissolution of Ce element in the glassy precursor coupled with nucleation and growth of Cu clusters via the precursor/solution interface. In the experiment of the degradation of methyl orange (MO) dye, the NPC fabricated by Cu-Ce metallic glasses exhibits superior sono-catalytic activity.

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    Effect of minor Sc addition on microstructure and stress corrosion cracking behavior of medium strength Al-Zn-Mg alloy
    Zhaoming Li, Haichang Jiang, Yunli Wang, Duo Zhang, Desheng Yan, Lijian Rong
    J. Mater. Sci. Technol., 2018, 34 (7): 1172-1179.  DOI: 10.1016/j.jmst.2017.11.042
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    Influence of Sc content on microstructure and stress corrosion cracking behavior of medium strength Al-Zn-Mg alloy have been investigated by optical microscopy, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and slow strain rate test. The results indicate that the addition of Sc results in the formation of the quaternary coherent Al3(Sc, Zr, Ti) dispersoids during homogenization treatment, which will inhibit the dynamic recrystallization behavior. The number density of Al3(Sc, Zr, Ti) particles increases with the increase of Sc content, and thus the recrystallization fraction of hot-extruded alloy is reduced and the peak strength in two-stage artificial aging sample is enhanced. At the same time, the wide of precipitation free zone is reduced, and the content of Zn and Mg in grain boundary particles and precipitation free zone is increased with the increase of Sc content. In peak-aged state, the 0.06 wt% Sc added alloy shows the better stress corrosion cracking resistance than the Sc-free alloy because of the reduction of recrystallization fraction and the interrupted distribution of grain boundary precipitates along grain boundary. However, the further addition of Sc to 0.11 wt% will result in the deterioration of stress corrosion cracking resistance due to the increase of electrochemical activity of grain boundary particles and precipitation free zone as well as hydrogen embrittlement.

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    Brazing of WC-8Co cemented carbide to steel using Cu-Ni-Al alloys as filler metal: Microstructures and joint mechanical behavior
    Xiangzhao Zhang, Guiwu Liu, Junnan Tao, Yajie Guo, Jingjing Wang, Guanjun Qiao
    J. Mater. Sci. Technol., 2018, 34 (7): 1180-1188.  DOI: 10.1016/j.jmst.2017.11.040
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    Three novel Cu-Ni-Al brazing filler alloys with Cu/Ni weight ratio of 4:1 and 2.5-10 wt% Al were developed and characterized, and the wetting of three Cu-Ni-Al alloys on WC-8Co cemented carbide were investigated at 1190-1210 °C by the sessile drop technique. Vacuum brazing of the WC-8Co cemented carbide to SAE1045 steel using the three Cu-Ni-Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5° and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu-Ni-Al/WC-8Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions (such as diffusion and solid solution) of WC-8Co/Cu-Ni-Al/steel system. Compared with the other two brazed joints, the WC-8Co/Cu-19Ni-5Al/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 min, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu-Ni-Al/WC-8Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.

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    Effect of stress ratio on very high cycle fatigue properties of Ti-10V-2Fe-3Al alloy with duplex microstructure
    Ying Wu, Jianrong Liu, Hao Wang, Shaoxuan Guan, Rui Yang, Hongfu Xiang
    J. Mater. Sci. Technol., 2018, 34 (7): 1189-1195.  DOI: 10.1016/j.jmst.2017.11.036
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    In fatigue critical applications, Ti-10V-2Fe-3Al alloy components are expected to endure cyclic loading with cycles above 109. To assess their operating safety, S-N relations of Ti-10V-2Fe-3Al alloy in very high cycle fatigue (VHCF) regime are of concern and have been investigated in this work. Fatigue behavior including S-N curves and crack initiation mechanisms is reported. Two transitions of fatigue crack initiation mechanism, from internal crack initiation to surface crack initiation and from αp cleavage to αs/β decohesion, occur when the stress ratio (R) and stress level are reduced. Fatigue limits exist at Nf = 6 × 107 cycles for all stress ratios except for 0.5. In the VHCF regime two kinds of internal crack initiation mechanisms exist, i.e., coalescence of cluster of αp facets and αs/β decohesion. Their mutual competition depends on the stress ratio and can be interpreted in terms of different stress character required for promotion on different internal crack initiation mechanism. Small crack propagation is discussed to be life controlling process under the stress ratio range from -0.5 to 0.1 during VHCF regime while under the stress ratio 0.5 VHCF, life almost refers to the life required for crack initiation.

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    Effect of 2-6 at.% Mo addition on microstructural evolution of Ti-44Al alloy
    S.Z. Zhang, Z.W. Song, J.C. Han, C.J. Zhang, P. Lin, D.D. Zhu, F.T. Kong, Y.Y. Chen
    J. Mater. Sci. Technol., 2018, 34 (7): 1196-1204.  DOI: 10.1016/j.jmst.2017.10.012
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    In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44Al alloy have been studied in this work. The as-cast microstructure morphology changes from (γ2) lamellar colony and β/β0 + γ mixture structure to β/β0 phase matrix widmannstatten structure, when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and α phase, the angles between the lamellar orientation and the block β/β0 phase are roughly at 0°, 45° and 90°. Comparing with heat treatment microstructure, the hot compression microstructure contains less β/β0 phase, however, the β/β0 phase containing 2Mo alloy and 3Mo alloy hot compressed at 1275 °C has the inverse tendency. In addition, (α2 + γ) colony is decomposed by the discontinuous transformation.

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    Experimental and numerical investigations on fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints
    Xiaomei Liu, Hao Cui, Shangzhou Zhang, Haipo Liu, Gaofeng Liu, Shujun Li
    J. Mater. Sci. Technol., 2018, 34 (7): 1205-1213.  DOI: 10.1016/j.jmst.2017.09.020
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    The fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints was studied by high-frequency fatigue test and finite element (FE) methods. The fatigue test results showed that a better enhancement of fatigue life was achieved for the joints with high-locked bolts by employing the combinations of cold expansion, interference fit, and clamping force. The fractography revealed that fatigue cracks propagated tortuously; more fatigue micro-cliffs, tearing ridges, lamellar structure were observed, and fatigue striation spacing was simultaneously reduced. The evaluation of residual stress conducted by FE methods confirmed the experimental results and locations of fatigue crack initiation. The extension of fatigue lives can be attributed to the evolution of fatigue damage and effect of beneficial compressive residual stresses around the hole, resulting in the delay of crack initiation, crack deflection, and plasticity-induced crack closure.

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    Effect of stress profile on microstructure evolution of cold-drawn commercially pure aluminum wire analyzed by finite element simulation
    Y.K. Zhu, Q.Y. Chen, Q. Wang, H.Y. Yu, R. Li, J.P. Hou, Z.J. Zhang, G.P. Zhang, Z.F. Zhang
    J. Mater. Sci. Technol., 2018, 34 (7): 1214-1221.  DOI: 10.1016/j.jmst.2017.07.011
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    The evolution of microstructure in the drawing process of commercially pure aluminum wire (CPAW) does not only depend on the nature of materials, but also on the stress profile. In this study, the effect of stress profile on the texture evolution of the CPAW was systematically investigated by combining the numerical simulation and the microstructure observation. The results show that the tensile stress at the wire center promotes the formation of <111> texture, whereas the shear stress nearby the rim makes little contribution to the texture formation. Therefore, the <111> texture at the wire center is stronger than that in the surface layer, which also results in a higher microhardness at the center of the CPAW under axial loading.

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    Microstructure, tensile properties and creep behavior of Al-12Si-3.5Cu-2Ni-0.8Mg alloy produced by different casting technologies
    Lijie Zuo, Bing Ye, Jian Feng, Xiangyang Kong, Haiyan Jiang, Wenjiang Ding
    J. Mater. Sci. Technol., 2018, 34 (7): 1222-1228.  DOI: 10.1016/j.jmst.2017.06.011
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    The relationship between the as-cast microstructure and mechanical properties of the Al-12Si-3.5Cu-2Ni-0.8Mg alloys produced by permanent mold casting (PMC) and high pressure die casting (HPDC) is investigated. The alloys in both PMC and HPDC consist of Al, Si, Al5Cu2Mg8Si6, Al3CuNi, and Al7Cu4Ni phase. However, the microstructure of the HPDC alloy is significantly refined. Compared to the PMC alloy, the ultimate tensile strength of the HPDC alloy is significantly increased from 244 MPa to 310 MPa, while the elongation shows a reverse trend at room temperature. At low stress and temperature range, slight variations of stress exponent and activation energy indicate that the minimum creep rate is controlled by the grain boundary creep. Then the minimum creep rate is higher for the specimen with the smaller grain size, where grain boundary creep is the dominant creep mechanism. At high stress region, the stress exponent for the PMC alloy and HPDC alloy is 5.18 and 3.07, respectively. The different stress exponents and activation energies measured at high stress and high temperature range indicates that the creep mechanism varies with the casting technologies.

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    Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy
    Hongmin Jia, Xiaohui Feng, Yuansheng Yang
    J. Mater. Sci. Technol., 2018, 34 (7): 1229-1235.  DOI: 10.1016/j.jmst.2017.06.009
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    Microstructure and crystallographic orientation of directionally solidified Mg-4 wt% Zn alloy were characterized by X-ray computed tomography (XCT) and electron backscatter diffraction (EBSD) in this study. Results reveal that Mg-4 wt% Zn alloy with dendritic microstructure exhibits typical {0002} basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy in 0.9 wt% NaCl solution was investigated. Result shows that {0002} oriented planes have better corrosion resistance than {11\(\overline{2}\)0} and {10\(\overline{1}\)0} ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film.

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    Effect of solute atom concentration and precipitates on serrated flow in Mg-3Nd-Zn alloy
    W.H. Wang, D. Wu, R.S. Chen, X.N. Zhang
    J. Mater. Sci. Technol., 2018, 34 (7): 1236-1242.  DOI: 10.1016/j.jmst.2017.06.004
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    Influence of solute atom concentration and precipitates on serrated flow, i.e., Portevin-Le Chatelier effect, was studied in Mg-3Nd-Zn alloy by tensile test at 250 °C with a strain rate of 1 × 10-3 s-1. Microstructure and tensile property of the Mg-3Nd-Zn alloy in solution and aging conditions were also investigated. Results indicate that the serrated flow was weakened with aging time, and geometry of the serrations changed from sharp to rounded corner. Through analyzing the mechanism of the interactions between dislocations and solute atoms, it was identified that the precipitates did not only weaken the serrated flow due to the decrease in the concentration of solute atom, but also regulate the serration type by restraining the movement of dislocations during high temperature deformation.

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    Effect of matrix sub-layer interfacial fracture on residual strength improvement of the fatigued carbon/carbon composites
    Jing Cheng, He-jun Li, Shou-yang Zhang, Li-zhen Xue
    J. Mater. Sci. Technol., 2018, 34 (7): 1243-1249.  DOI: 10.1016/j.jmst.2017.05.010
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    :In the present study, flexural behavior of carbon fiber reinforced pyrolytic carbon matrix composites (C/C composites) before and after fatigue tests had been studied. The results showed that the residual flexural strengths of the samples had been improved after fatigue tests, and the fracture mechanisms of the original and post-fatigue specimens had some differences. Fracture mechanism of the original specimens could be described as fiber/matrix interfacial de-bonding, and the dominant damage of the post-fatigue specimens could be regarded as pyrolytic carbon sub-layers’ step-delamination. The degradation of matrix sub-layer interfacial bonding strength was beneficial to improve the mechanical properties of C/C composites.

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    Two-stage double peaks ageing and its effect on stress corrosion cracking susceptibility of Al-Zn-Mg alloy
    Y.L. Wang, H.C. Jiang, Z.M. Li, D.S. Yan, D. Zhang, L.J. Rong
    J. Mater. Sci. Technol., 2018, 34 (7): 1250-1257.  DOI: 10.1016/j.jmst.2017.05.008
    Abstract   HTML   PDF

    Different artificial two-stage ageing behaviors and their effect on stress corrosion cracking (SCC) susceptibility of Al-Zn-Mg alloy have been investigated. The experimental results show that two hardness peaks present on the second-stage ageing-hardening curve when the first-stage ageing is dealt with comparatively lower temperature than the conventional one. The first peak is caused by dispersive and evenly distributed G.P. zones, while η′ phases and coarsened G.P. zones contribute to the second peak. Tensile strength of experimental alloy raises 9.6% (33.2 MPa) and SCC susceptibility decreases 38.9% by applying the second peak ageing regime instead of conventional T73. Al-Zn-Mg alloy obtains high strength and SCC resistance due to its finely dispersive matrix precipitates (MPts), coarsened and discontinuous grain boundary precipitates (GBPs), as well as the narrow precipitate free zone (PFZ) in the second peak ageing condition.

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