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ISSN 1005-0302
CN 21-1315/TG
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      10 April 2016, Volume 32 Issue 4 Previous Issue    Next Issue
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    Orignal Article
    Hot Deformation Behaviour of SiC/AA6061 Composites Prepared by Spark Plasma Sintering
    Xiaopu Li, Chongyu Liu, Kun Luo, Mingzhen Ma, Riping Liu
    J. Mater. Sci. Technol., 2016, 32 (4): 291-298.  DOI: 10.1016/j.jmst.2015.12.006
    Abstract   HTML   PDF
    In this study, SiC/AA6061 composites with different SiC volume fractions (5%, 10%, 15% and 20%) were fabricated by spark plasma sintering. The deformation behaviour of the composites was studied by uniaxial compression test at temperatures from 573 K to 773 K and strain rates between 0.001 s-1 and 1 s-1. Results indicate that the flow stress of SiC/AA6061 composites increases with the increase of SiC volume fraction, with the decrease of deformation temperature and with the decrease of strain rate. The main deformation mechanism of the composites is dynamic recrystallisation (DRX), and the DRX degree depends on the processing parameters of deformation. Higher SiC volume fraction, higher deformation temperature and lower deformation strain rate promote the occurrence of DRX. The strain rate sensitivity and deformation activation energy of SiC/AA6061 composites are calculated. Results show that with the increase in deformation temperature and the decrease in SiC volume fraction, the strain rate sensitivity of the composites increases. From 573 K to 773 K, the average deformation activation energy of 5vol.%SiC/AA6061, 10vol.%SiC/AA6061, 15vol.%SiC/AA6061 and 20vol.%SiC/AA6061 are 207.91, 230.88, 237.7 and 249.87 kJ mol-1, respectively. The optimum hot working zone of the SiC/AA6061 composites is in the temperature range of 723 K to 773 K at strain rates from 0.1 s-1 to 1 s-1.
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    Microstructure and Mechanical Properties of Overcast 6101-6101 Wrought Al Alloy Joint by Squeeze Casting
    Teng Liu, Qudong Wang, Yudong Sui, Qigui Wang
    J. Mater. Sci. Technol., 2016, 32 (4): 298-305.  DOI: 10.1016/j.jmst.2015.11.020
    Abstract   HTML   PDF
    The wrought Al alloy-wrought Al alloy overcast joint was fabricated by casting liquid 6101 Al alloy onto 6101 Al extrusion bars and solidifying under applied pressure. The joint interfacial microstructure was investigated; the effect of applied pressure on the microstructure and mechanical properties was evaluated. The mechanism of joint formation and mechanical behaviors of both squeeze cast 6101 and 6101-6101 overcast joint material were analyzed. The results show that with the application of pressure during solidification process, wrought Al alloy 6101 could be cast directly into shape successfully. Excellent metallurgical bonding was then formed in the overcast joint by electro-plating 6101 solid insert with a layer of zinc coating, and a transition zone formed in the joint region. During the tensile test, the fracture occurs in the 6101 solid insert part with the ultimate tensile strength (UTS) of 200 MPa, indicating that the strength of the overcast joint is higher than 200 MPa, and the tensile strength of overcast joint material is independent on the magnitude of applied pressure. For Al-Al overcast joint material, if a clean and high strength joint is formed, the UTS and yield strength (YS) are determined by the material with the lower value, while for EL, the value is determined by the length proportion and the stress-strain behavior of both components.
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    Effect of Fe, Si and Cooling Rate on the Formation of Fe- and Mn-rich Intermetallics in Al-5Mg-0.8Mn Alloy
    Yulin Liu, Lei Luo, Chaofei Han, Liangyun Ou, Jijie Wang, Chunzhong Liu
    J. Mater. Sci. Technol., 2016, 32 (4): 305-313.  DOI: 10.1016/j.jmst.2015.10.010
    Abstract   HTML   PDF
    The Fe- and Mn-rich intermetallics are of great effect on the mechanical properties of the AA5083 type alloy (Al-5Mg-0.8Mn). The effect of Fe, Si and cooling rate on the formation of the intermetallics were investigated by analyzing the microstructures of the alloys with different Fe and Si contents. The results indicated that increasing the Fe content resulted in the increase of the Al6(Fe,Mn) phase in both amount and size. In the alloys with high Fe content, the platelet-like Al6(Fe,Mn) compounds lined up and formed a band. Increasing the content of Si resulted in the increase of the Mg2Si phase which formed a network structure. Increasing the cooling rate significantly refined the intermetallics. However, increasing the cooling rate did not change the characteristic of the intermetallic compounds in the alloys with low or medium Si contents. For the alloys with high contents of Fe and Si under the condition of near-rapid cooling, the Fe- and Mn-rich intermetallic compound changed to the quaternary Al15(Fe,Mn)3Si phase and displayed a fine fish bone or Chinese script structure. The refinement of the intermetallics would allow higher tolerance of Fe and Si contents in the AA5083 alloy produced, for instance, via the continuous strip casting process.
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    Effects of Extrusion Speed on the Microstructure and Mechanical Properties of Mg-9Gd-3Y-1.5Zn-0.8Zr alloy
    Xuan Liu, Zhiqiang Zhang, Wenyi Hu, Qichi Le, Lei Bao, Jianzhong Cui
    J. Mater. Sci. Technol., 2016, 32 (4): 313-319.  DOI: 10.1016/j.jmst.2015.12.004
    Abstract   HTML   PDF
    The effects of the extrusion speed on the microstructures, mechanical properties and aging hardening behaviors of Mg-9Gd-3Y-1.5Zn-0.8Zr alloy have been investigated. The microstructure evolution during hot extrusion has also been discussed. The microstructures of the extruded alloys mainly consist of the equiaxed dynamically recrystallized grains and fiber-like long period stacking ordered (LPSO) phase. The increasing extrusion speed results in grain coarsening and the mechanical properties deterioration. Meanwhile, it could also retard the aging hardening response. The extrudability of the investigated alloy is limited. Cracks nucleate and grow up rapidly when the extrusion speed is over 0.3 m/min. It should be closely related to the large amount of LPSO phase and the unique microstructure evolution. The rapidly precipitating fine lamella during extrusion could pin the dislocations and grain boundaries effectively. It could strengthen the alloy but also limit the extrudability of the investigated alloy.
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    Microstructure and Mechanical Properties of Al2O3/ZrO2 Directionally Solidified Eutectic Ceramic Prepared by Laser 3D Printing
    Zhi Liu, Kan Song, Bo Gao, Tian Tian, Haiou Yang, Xin Lin, Weidong Huang
    J. Mater. Sci. Technol., 2016, 32 (4): 320-325.  DOI: 10.1016/j.jmst.2015.11.017
    Abstract   HTML   PDF
    Directionally solidified eutectic ceramics such as Al2O3/ZrO2 are promising structural materials for applications in harsh environment with an ultrahigh temperature. In this work, through adopting assistant heating laser 3D printing, Al2O3/ZrO2 eutectic samples were manufactured with suppressing the formation of cracks. The dependence of the average rod spacing (λav) on the scanning rate (V) follows a relation with λavV0.5 = 1 µm1.5 s-0.5. Typical eutectic microstructures, so-called complex regular, were analyzed with respect to its evolution with modulating the growth conditions. Formation mechanism of the solidification defect, shrinkage porosity, was discussed and the defect is found to be significantly suppressed by optimizing the solidification parameters. The maximum hardness and fracture toughness are measured to be 16.7 GPa and 4.5 MPa m1/2, respectively. The interplay between the propagation of cracks and the Al2O3/ZrO2 interface is discussed.
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    Effect of Rotation Rate on Microstructure and Mechanical Properties of Friction Stir Spot Welded DP780 Steel
    G.M. Xie, H.B. Cui, Z.A. Luo, W. Yu, J. Ma, G.D. Wang
    J. Mater. Sci. Technol., 2016, 32 (4): 326-333.  DOI: 10.1016/j.jmst.2015.10.009
    Abstract   HTML   PDF
    DP780 steel sheets consisting of ferrite and martensite were successfully friction stir spot welded (FSSW) at the rotation rates of 500 to 1500 r/min using a W-Re alloy tool. The effect of rotation rate on microstructure and mechanical properties of the FSSW DP780 was investigated. The peak temperatures in the welds at various rotation rates were identified to be above A3 temperature. FSSW caused the dynamic recrystallization in the stir zone (SZ), thereby producing the fine equiaxed grain structures. At the higher rotation rates of ≥1000 r/min, a full martensitic structure was observed throughout the SZs, whereas at the lower rotation rate of 500 r/min, the SZ consisted of a fine dual phase structure of ferrite and martensite due to the action of deformation induced ferrite transformation. The maximum average failure load as high as 18.2 kN was obtained at the rotation rate of 1000 r/min and the fracture occurred at the thinned upper sheet.
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    Influence of Conductivity on Corrosion Behavior of 304 Stainless Steel in High Temperature Aqueous Environment
    Jiazhen Wang, Jianqiu Wang, En-Hou Han
    J. Mater. Sci. Technol., 2016, 32 (4): 333-340.  DOI: 10.1016/j.jmst.2015.12.008
    Abstract   HTML   PDF
    The influence of conductivity on corrosion behavior of 304 stainless steel (SS) in high temperature water was investigated by using in-situ potentiodynamic polarization curves, electrochemical impedance spectra (EIS) at 300 °C, and ex-situ scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The structures of oxide films formed on 304 SS change with different conductivities at 300 °C. With the increase in conductivity, the passive current density increases while the resistances of oxide films decrease. But the resistances do not decrease lineally with the increase in conductivity. A modified double-layer model for oxide structure was proposed to explain the influence mechanism of conductivity on the oxide films on 304 SS in high temperature water. Improving the 10B enrichment level can reduce the conductivity of primary water and increase the corrosion resistance of 304 SS.
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    Effects of Cl- Ions on the Corrosion Behaviour of Low Alloy Steel in Deaerated Bicarbonate Solutions
    Yunfei Lu, Junhua Dong, Wei Ke
    J. Mater. Sci. Technol., 2016, 32 (4): 341-348.  DOI: 10.1016/j.jmst.2015.11.015
    Abstract   HTML   PDF
    The effect of Cl- ions on corrosion evolution of NiCu low alloy steel during immersion tests (up to 70 days) in deaerated 0.05 mol/L bicarbonate solutions was investigated by in-situ electrochemical measurements combined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) characterisations. The results showed that due to the acceleration of substrate dissolution in the presence of Cl-, corrosion of NiCu low alloy steel underwent only two stages, i.e., a quick oxidation process followed by a final metastable passive state, without the initial slow anodic dissolution as observed in the Cl--free bicarbonate solution. The main components of the formed rust layer in the Cl--free bicarbonate solution were α-FeOOH and Fe3O4, while apart from α-FeOOH, Fe6(OH)12CO3 was found evident instead of Fe3O4 in the Cl--containing solution. Metastable pits were only found in the Cl--containing solution where Cl- accumulated after the immersion test, confirming the attack of Cl- on the substrate after penetrating the formed corrosion product layer.
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    Glass-forming Ability and Corrosion Resistance of Zr——Cu——Al——Co Bulk Metallic Glass
    W. Zhou, W.P. Weng, J.X. Hou
    J. Mater. Sci. Technol., 2016, 32 (4): 349-354.  DOI: 10.1016/j.jmst.2015.12.012
    Abstract   HTML   PDF
    Investigations were carried out to examine the effects of Co addition on the glass-forming ability (GFA) and corrosion resistance of Zr46Cu46Al8 bulk metallic glass in chloride-containing solution. It is found that the GFA of (Zr46Cu46Al8)100-xCox (x = 0, 1, 2, and 4 at.%) alloys reduces with the increase in Co content and correlates well with the parameters, such as the supercooled liquid region width ΔTx, the reduced glass transition temperature Trg and γ. The corrosion resistance is however found to be enhanced with the increase in Co concentration. The addition of Co causes the enrichment of Zr and Al, but depletes Cu in the surface films, which effectively enhances the corrosion potential and lowers the corrosion current density.
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    Microstructure of Electrodeposited Cu Micro-cylinders in High-Aspect-Ratio Blind Holes and Crystallographic Texture of the Cu Overburden Film
    Yazhou Zhang, Guifu Ding, Hong Wang, Ping Cheng
    J. Mater. Sci. Technol., 2016, 32 (4): 355-361.  DOI: 10.1016/j.jmst.2015.09.008
    Abstract   HTML   PDF
    Microstructure and texture of electrodeposited Cu micro-cylinders in the blind hole play a vitally important role in the electrical and mechanical properties of the three-dimensional (3-D) IC (integrated circuit)/Si integrations. In this paper, a new commercial additive system, which is specifically developed for the high-aspect-ratio through-silicon-via (TSV) filling, was used to electrodeposit Cu in the blind holes. The microstructure of electrodeposited Cu micro-cylinder in the blind hole with a diameter of 40 µm and a depth of 140 µm was investigated by electron back-scattered diffraction (EBSD) technique. Grain size distribution of the Cu micro-cylinder in the blind hole differed from the bottom to the top. The grain boundaries contained a high fraction of Σ3 CSL (coincident site lattice) boundaries. It has been reported that the Cu overburden film on the surface of the blind hole influenced the crystallographic orientation of Cu grains inside the damascene trench. So the effects of the current density and additive concentration on the crystal structure of the overburden Cu film were also studied in this study. The experimental results indicated that the preferred orientation of the Cu overburden film changed from {111} to {220} when the current density increased from 2 to 80 mA cm-2. However, the effect of additives on the crystal structure of the Cu overburden film was dependent on the crystal structure of the seed layer.
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    Influence of Processing Conditions on Microstructure and Mechanical Properties of Large Thin-Wall Centrifugal Ti-6Al-4V Casting
    Xin Feng, Jianke Qiu, Yingjie Ma, Jiafeng Lei, Yuyou Cui, Xinhua Wu, Rui Yang
    J. Mater. Sci. Technol., 2016, 32 (4): 362-371.  DOI: 10.1016/j.jmst.2015.12.010
    Abstract   HTML   PDF
    In this work, the effects of mould pre-heating temperatures and hot isostatic pressing (HIPping) process on the microstructural characteristics and mechanical properties, including static tensile and damage-tolerance properties of large thin-wall cylindrical Ti-6Al-4V casting, have been studied. The experimental results show that with the increasing mould pre-heating temperature from 673 to 873 K, the casting microstructures change from a mixture of Widmanstätten and colony microstructure to a primary colony. The centre of the thick wall section has relatively coarse microstructure than the edge and thin section. Lower mould pre-heating temperature brings about more porosities. HIPping process, which not only reduces the casting pores effectively but also increases the prior β grain boundary cohesion and coarsens the microstructure, is essential to improving the ductility of the casting. Due to the oxygen contamination and finer microstructure on the surface, micro-hardness profiles on the cross section present a decreasing tendency from the surface to inner. The thickness of the reaction layers for the different mould pre-heating temperatures is nearly the same (~450 µm). On the whole, the tensile strength and micro-hardness decrease with increasing mould pre-heating temperature from 673 to 873 K. However, the fracture toughness and fatigue crack growth resistance of the castings increase with increasing mould pre-heating temperature.
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    Microstructures and Mechanical Properties of Vacuum Brazed Ti3Al/TiAl Joints Using Two Ti-based Filler Metals
    H.S. Ren, H.P. Xiong, B. Chen, S.J. Pang, B.Q. Chen, L. Ye
    J. Mater. Sci. Technol., 2016, 32 (4): 372-380.  DOI: 10.1016/j.jmst.2015.11.018
    Abstract   HTML   PDF
    Vacuum brazing of Ti3Al-based alloy to TiAl was firstly carried out by Ti——15Cu——15Ni (wt%) filler metal. A continuous Ti3Al band, Ti2Ni and Ti2Cu/Cu3Ti phases formed and the joint showed a shear strength of 53.8-112.4 MPa at room temperature. For the improvement of the joint strength, a new Ti——Zr——Cu——Ni——Fe filler alloy was designed, and its wettability on Ti3Al and TiAl substrate was studied with the sessile drop method. After holding for 20 min at 1010 °C the Ti——Zr——Cu——Ni——Fe filler showed a low contact angle of 20° and 21° on Ti3Al and TiAl substrate, respectively. The joint brazed with this novel filler mainly consisted of Ti-rich area, Ti3Al reaction layer and residual filler metal. With the increase of the brazing temperature, the amount of residual filler metal decreased and the Ti3Al reaction layer thickened. The Ti3Al/TiAl joint brazed with Ti——Zr——Cu——Ni——Fe filler exhibited a lower hardness than that brazed with Ti——Cu——Ni filler. The corresponding joints brazed at 950 °C for 5 min presented the shear strength of 257.6 ± 33.6 MPa at room temperature and 304.8 ± 9.9 MPa at 600 °C.
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    Solidification Microstructure of Laser Additive Manufactured Ti——6Al——2Zr——2Sn——3Mo——1.5Cr——2Nb Titanium Alloy
    Qiang Zhang, Jing Chen, Lilin Wang, Hua Tan, Xin Lin, Weidong Huang
    J. Mater. Sci. Technol., 2016, 32 (4): 381-386.  DOI: 10.1016/j.jmst.2015.11.019
    Abstract   HTML   PDF
    Solidification microstructure of powder fed laser additive manufactured Ti——6Al——2Zr——2Sn——3Mo——1.5Cr——2Nb titanium alloy was investigated. The results showed that by deliberately increasing the powder feed rate, partially melted powders were retained at the top of the molten pool, which can promote heterogeneous nucleus. Thus, each cladding layer is composed of two regions: (i) randomly orientated cellular structure region caused by partially melted powders at the top of each cladding layer; and (ii) epitaxial cellular structure region adjacent to the fusion line. Usually, randomly orientated cellular structure region was totally remelted for a wide range of process conditions. The remelting effect ensures the continuity of epitaxial growth of cellular structure and leads to the formation of columnar β grains. In order to obtain equiaxed grains the scanning velocity and powder feed rate should be carefully selected to enlarge the randomly orientated cellular structure region.
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ISSN: 1005-0302
CN: 21-1315/TG
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