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      20 April 2014, Volume 0 Issue 4 Previous Issue    Next Issue
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    Research of Graphene-reinforced Aluminum Matrix Nanocomposites
    YAN Shao-jiu, YANG Cheng, HONG Qi-hu, CHEN Jun-zhou, LIU Da-bo, DAI Sheng-long
    2014, 0 (4): 1-6.   DOI: 10.3969/j.issn.1001-4381.2014.04.001
    Abstract ( 3194 ( PDF (3277KB)( 1859 Citation
    Graphene-reinforced aluminum matrix nanocomposites were successfully synthesized through ball milling and powder metallurgy. The tensile strength and yield strength of graphene-reinforced aluminum matrix nanocomposites are remarkably enhanced by adding graphene nanoflakes(GNFs). Importantly, the ductility properties are remained excellently, which is firstly found in the second phase reinforced metal matrix nanocomposites. The microstructures were observed by OM, SEM and TEM method. And the tensile properties were tested.The results show that graphene nanoflakes are effectively dispersed and well consolidate with aluminum matrix, however, chemical reactions are not observed. The original structured characteristics of graphene nanoflakes are preserved very well. The average tensile strength and yield strength of nanocomposite are 454MPa and 322MPa, respectively,which are 25% and 58% higher than the pristine aluminum alloy at a nanofiller mass fraction of 0.3%, while the ductility increases slightly. The relevant mechanisms of strengthening and toughening enhancement are discussed on the base of 2D and wrinkled structured properties of graphene nanoflakes.
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    Effect of Aluminum Content on Al-Fe-Si/Al In-situ Composites
    ZHAO Long-zhi, JIAO Yu
    2014, 0 (4): 7-12.   DOI: 10.3969/j.issn.1001-4381.2014.04.002
    Abstract ( 931 ( PDF (3013KB)( 281 Citation
    The Al-Fe-Si/Al in-situ composite was prepared by the powder metallurgy transient liquid phase sintering method. The influence of Al content on microstructure, hardness and wear resistance of in-situ composites was investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and M-2000 wear tester. The results show that the coarse FeAl phases disappear; the needle shape-like Al0.5FeSi0.5 intermetallic compound reinforcement grows into short bar when the content of aluminum increases. When the mass fraction of aluminum is 77%, the fine short-bar Al0.5FeSi0.5 reinforcement distributes meanly in the matrix, the hardness of composites has a peak value(283.7), which is 8 times that of pure aluminum and 2.5 times that of aluminum silicon alloy. The wear resistance is the best (wear rate is 0.3781%),which is 6.6 times that of pure aluminum and 4.5 times that of aluminum silicon alloy. The wear mechanism is mainly abrasive wear.
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    Microstructure and Mechanical Properties of Ti3Al/GH4169 Superalloy Joints Arc Welded with NiCuNbCr Filler Alloy
    CHEN Bing-qing, XIONG Hua-ping, GUO Shao-qing, ZHANG Xue-jun, SUN Bing-bing, TANG Si-yi
    2014, 0 (4): 13-17,25.   DOI: 10.3969/j.issn.1001-4381.2014.04.003
    Abstract ( 942 ( PDF (1738KB)( 382 Citation
    With a NiCuNbCr alloy as filler material, dissimilar welding of a Ti3Al-based alloy and a Ni-based superalloy (GH4169) was successfully carried out using gas tungsten arc (GTA) welding technology. The microstructure evolution along the cross section of the dissimilar joint was analyzed with the scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (XEDS) method.The results show that, both the GH4169/weld interface and the weld consist of Ni solid solution, dissolve with several elements of Cu, Fe, Cr and Nb. The weld/Ti3Al interface is composed of three transitional layers. The phase constitutions of the layers from the Ti3Al side to weld are: Ti2AlNb matrix dissolving with Ni and Cu, Al(Ni, Cu)2Ti intermetallics as well as (Nb, Ti, Mo) solid solution; (Ni, Nb, Cr) and Ni(Cu, Ti) solid solution; Ni solid solution, dissolving with Cu, Nb and Cr, respectively. The average room-temperature tensile strength of the joints is 140.7MPa. The fracture occurrs at the diffusion reaction layer at the surface of the joined Ti3Al base alloy, which is mainly composed of Ti2AlNb matrix dissolving with Ni and Cu as well as Al(Ni, Cu)2Ti intermetallics. This interface should be the weak link of the Ti3Al/GH4169 joint.
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    Effect of Microstructure on Corrosion Resistance of Spring Steels Before and After Heat Treatment
    TIAN Jun, XUE Shun, WU Cheng-chuan, CHENG Guo-guang, ZHOU Guo-zhi, WANG Wen-hu, SHENG Wei
    2014, 0 (4): 18-25.   DOI: 10.3969/j.issn.1001-4381.2014.04.004
    Abstract ( 1122 ( PDF (6213KB)( 246 Citation
    The salt-spray tests were conducted for different composition spring steel specimens before and after heat treatment, and polarization curve of those specimens were measured. Morphologies and composition of scale on the surface of specimens were analyzed by scanning electron microscope (SEM), energy disperse spectroscope(EDS) and X-ray diffraction(XRD). The effect of different microstructure on corrosion resistance of spring steels before and after heat treatment was studied.The results show that the microstructure before and after heat treatment of spring steels has an impact on their corrosion resistance, particularly in the early stages of corrosion. Corrosion products of spring steels in NaCl aqueous solution mainly are β-FeOOH. Pearlite + ferrite steel has higher corrosion potential, bigger corrosion current density and faster corrosion rate than tempered troostite steel. But corrosion resistance of the former is better than the latter's over time.The reason of which is the anchor function of cementite for scale, the cementite may help anchor the scale on the surface of spring steel. So the scale, corroding medium and oxygen can't contact with ferrous matrix.
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    Influence of Solution Heat Treatment on Localized Corrosion of 7A55 Aluminum Alloy
    ZHANG Xin-ming, WU Ze-zheng, LIU Sheng-dan, FENG Di, OUYANG Hui, WANG Ting
    2014, 0 (4): 26-33,39.   DOI: 10.3969/j.issn.1001-4381.2014.04.005
    Abstract ( 854 ( PDF (5601KB)( 469 Citation
    The influence of solution heat treatment on the localized corrosion of the 7A55 aluminum alloy were investigated by means of electrochemical test, immersion tests, optical microscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM).The results show that a large number of coarse constituent particles cause severe corrosion of the rolled plate and the entire surface is exfoliated. Single-stage solution treatment causes lower recrystallization fraction and small size of sub-grains, but the large number of remnant coarse particles results bad performance of corrosion resistance. The 450℃/1h+480℃/30min solution heat treatment results in improved dissolution of coarse second phase particles, low recrystallization percentage and small size of sub-grains. The results indicate that the 7A55 aluminum alloy has the best localized corrosion resistance under the condition of the 450℃/1h+480℃/30min solution heat treatment.
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    Effect of Bonded Area on Shear Strength and Failure Mode in Steel/Al CMT Brazed Joint
    YANG Shuo, LIN Jian, YANG Shang-lu, LEI Yong-ping, KONG De-ning
    2014, 0 (4): 34-39.   DOI: 10.3969/j.issn.1001-4381.2014.04.006
    Abstract ( 927 ( PDF (2484KB)( 247 Citation
    Effect of bonded area on shear strength and failure mode of galvanized low carbon steel/6061 Al alloy CMT brazed joint was studied. The results show that, with the increasing welding torch offset the bonded area of CMT joint decreases and the wetting angle increases. That leds to the decreasing of shear strength, and the joint failure position transferring from fused Al area to steel/aluminum interface layer. Based on the experimental results, a numerical model of lap-shear process of CMT joint considering the failure criterion of interface layer is established. The reason of bonded area influencing shear strength and failure mode of CMT joint is discussed.
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    Influence of Annealing Treatment on Microstructure and Plasticity of High-speed Electroformed Nickel
    LUO Yang, TIAN Wen-huai, SHI Gao-feng, CHENG Sheng-wei
    2014, 0 (4): 40-45.   DOI: 10.3969/j.issn.1001-4381.2014.04.007
    Abstract ( 836 ( PDF (2661KB)( 293 Citation
    The electroformed nickel was prepared by high-speed electroforming method.The influence of annealing temperature on microstructure and mechanical properties was investigated. The microstructures, residual stresses and Vickers hardness(HV) of electroformed nickel were detected by optical microscope, X-ray stressometer and micro-hardness tester.The elongation and tensile strength were measured by tensile tests. The results indicate that the electroformed nickel is divided into inner and outer two parts, the inner part is composed of coarse columnar grains, the outer part is composed of fine columnar grains.The recovery and recrystallization occur in the electroformed nickel during annealing. The elongation of electroformed nickel without any annealing is 14%, the Vickers hardness in the inner part is 193, in the outer part is 263 and the tensile strength σb is 625MPa. After annealing treatment at different temperatures, the plasticity can be improved, but the hardness and tensile strength decrease. After annealed at 550℃ for 2h the elongation of electroformed nickel is up to 32%, the Vickers hardness in the inner part is 173, in the outer part is 165 and the σb is 460MPa.
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    Growth of Radicals on CVD Diamond (001) Surface:First Principle Studies
    LIU Xue-jie, WEI Huai, REN Yuan, LU Feng, ZHANG Su-hui, YIN Yong-jie
    2014, 0 (4): 46-52.   DOI: 10.3969/j.issn.1001-4381.2014.04.008
    Abstract ( 870 ( PDF (4122KB)( 330 Citation
    The growth mechanism about CVD diamond films on (001) surface was studied with first-principle method which was based on density functional theory (DFT). The configurations of clean diamond surface and H-terminated diamond surface were calculated. The adsorption evolutions of H atoms and radicals (C, CH, CH2 and CH3) on the surface of diamond reconstruction and the surface of monolayer H-terminated diamond were analyzed. The results indicate that a clean diamond surface undergoes a symmetrical dimer reconstruction transformation and a monolayer H adsorbed on the surface can lead to stable of the diamond structure. In addition, H atoms can activate graphite and extract H to make a radical site when radicals are adsorbed on the diamond (001) surface. CH2 groups can better improve the growth rate of CVD diamond film than CH3 groups. CH2 group is the most efficient group in the process of CVD diamond film growth. CH group hinders the growth of CVD diamond film.
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    Influence of Ceramic-shot-peening on Surface Integrity of DD6 Single Crystal Superalloy
    WANG Xin, YOU Hong-de, LI Jia-rong, ZHAO Jin-qian, TANG Zhi-hui, LU Feng
    2014, 0 (4): 53-57.   DOI: 10.3969/j.issn.1001-4381.2014.04.009
    Abstract ( 1043 ( PDF (2678KB)( 272 Citation
    DD6 single crystal superalloy was employed to investigate the effect of ceramic-shot-peening on surface integrity, such as surface morphology, surface roughness,microstructure and microhardness.The results show that significant change of surface integrity takes place, and that severe plastic deformation is observed on the surface with the roughness Ra increasing. With the increasing of the Ra, stress concentration coefficient decreases when using the specific parameter. Dislocation multiplication occurrs on the phase γ and γ' of DD6 single-crystal superalloy after shot peening(SP), which induces structure hardening. Furthermore, the surface microhardness reaches 620, which is 44% higher than as-received after two SP processes.
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    Hardenability of Low Carbon Vanadium Microalloyed Steels
    LI Xiao-xian, SUN Xin-jun, YANG Geng-wei, LI Zhao-dong, YU Lan, YONG Qi-long
    2014, 0 (4): 58-62.   DOI: 10.3969/j.issn.1001-4381.2014.04.010
    Abstract ( 963 ( PDF (1936KB)( 361 Citation
    By using Jominy end quench test and combining with thermodynamic calculation of vanadium carbide precipitation, the influence of vanadium on the hardenability of low carbon steels was investigated. The results indicate that the hardenability of the experimental steels are improved by increasing the total content of V. The thermodynamic calculation results show that the concentration of V in solution increases with the increasing content of V in 0.22C steel at 880℃. The VC particles precipitate in austenite when the V content is more than 0.137%(mass fraction) in steel, and the concentration of C in solution decreases. The ideal critical diameter of experimental steels is calculated by comprehensive consideration of the concentration of V and C in solution and the prior austenite grain size.The variation trend of ideal critical diameter agrees well with the experimental results.
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    Preparation and Mechanical Properties of TiB2/WC/h-BN Self-lubricating Ceramic Material
    XU Xiu-guo, XU Chong-hai, FANG Bin, WANG Chun-lin, YI Ming-dong
    2014, 0 (4): 63-67.   DOI: 10.3969/j.issn.1001-4381.2014.04.011
    Abstract ( 849 ( PDF (1052KB)( 236 Citation
    TiB2/WC/h-BN self-lubricating ceramic material with the addition of solid lubricant h-BN was prepared with vacuum hot-pressing sintering technique. Mechanical properties and density were tested. The phase and microstructure of the material were analyzed by X-ray diffraction and SEM. The results show that the relative density of TiB2/WC/h-BN self-lubricating ceramic material is 97.5%, and its flexural strength, fracture toughness and Vickers hardness are 652MPa, 4.5MPa·m1/2 and 14.8GPa, respectively. Solid lubricant h-BN particles with flake structure are intact and uniformly distribute. It can effectively inhibit the growth of TiB2 matrix grains. The fracture of the material belongs to the mixture of transgranular/intragranular mode but mainly transgranular fracture. The toughening mechanisms are mainly crack bridging and crack deflection. The friction coefficient of TiB2/WC/h-BN self-lubricating ceramic material is lower than 0.3. Compared with the other self-lubricating ceramic materials added h-BN, TiB2/WC/h-BN self-lubricating ceramic material has better mechanical properties and friction behavior.
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    Microstructure and Tribological Behavior of Cold-sprayed Tin-bronze/Quasicrystal Composite Coating
    GUO Xue-ping, LI Wen-ya, LIAO Han-lin
    2014, 0 (4): 68-72,78.   DOI: 10.3969/j.issn.1001-4381.2014.04.012
    Abstract ( 812 ( PDF (2551KB)( 412 Citation
    Tin-bronze and tin-bronze/quasicrystal composite coatings were prepared by cold spray process. Optic microscope (OM), scanning electron microscope (SEM) and microhardness tester were used to examine microstructures and microhardness of the prepared coatings. Dry sliding tribological tests of the coatings were conducted in an ambient atmosphere, and the wear mechanisms were discussed according to the worn traces investigation. The influences of an incorporation of particulate quasicrystalline phase on the microstructure and tribological behavior of reinforced composite coating were investigated.The results show that the composite coating prepared by cold spraying of mechanically blended powder presents a lower porosity and a higher microhardness as compared to the monolithic bronze coating. Hard quasicrystal particles exhibit a relatively lower deposition efficiencies, and the composite coating has a slightly lower coefficient of friction and a higher wear rate, as compared to the bronze coating. The abrasive wear is mainly responsible for the tribological behavior of the composite coating.
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    Effect of Shot-peening on Fatigue Behavior of 6151-T6 Aluminum Alloy Under Rotating Bending
    ZHANG Yan-bin, LU Lian-tao, XUE Bi-yi
    2014, 0 (4): 73-78.   DOI: 10.3969/j.issn.1001-4381.2014.04.013
    Abstract ( 1020 ( PDF (2398KB)( 321 Citation
    The surface roughness of electro-polishing, shot-peening and polishing after shot-peening 6151-T6 aluminum alloy samples were measured together with Vickers hardness on the surface hardness layer of the shot-peening samples. Fatigue tests of the aluminum alloy with different surface conditions were performed under rotary bending loading. The residual stress on the surface for the shot-peening specimen was measured during the fatigue test, and the effect of shot-peening on fatigue behavior of the aluminum alloy was investigated. The results show that the effect of shot-peening on fatigue behavior of the material depends on the applied cyclic compressive stress level. Shot-peening improves fatigue life of the material when the compressive stress (sum of applied compressive stress and residual compressive stress) on the surface layer is below the cyclic yield strength of the layer. The great improvement of fatigue life is due to the fact that residual compressive stress induced by shot-peening cannot be released during fatigue tests. On the contrary, the residual compressive stress can be released when the compressive stress on the surface layer exceeds the cyclic yield strength of the layer. The improvement degree of fatigue life is affected by the extent of residual stress relaxation on the surface. Besides, the surface roughness induced by shot-peening slightly decreases the fatigue life of the material in the full stress amplitude range.
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    Effect of Fibers Orientation on Torsional Fretting Wear Behaviors of Carbon Fiber Fabric Composites
    ZUO Kong-cheng, CAI Zhen-bing, SONG Chuan, PENG Jin-fang, MO Ji-liang, SHEN Huo-ming, ZHU Min-hao
    2014, 0 (4): 79-84.   DOI: 10.3969/j.issn.1001-4381.2014.04.014
    Abstract ( 958 ( PDF (4813KB)( 255 Citation
    Under the contact configuration of ball-on-flat, the torsional fretting wear experimental research between carbon fiber fabric composites and GCr15 steel ball was carried out. The influence of fiber orientation on fretting wear properties was discussed. The results show that, similar to the metal materials, the carbon fiber fabric composites is still existed in three fretting running regimens, i.e. partial slip regime (PSR), mixed regime(MR) and slip regime(SR). The torsional fretting wear mechanisms of carbon fiber fabric composites are abrasive and oxidative wear. The friction and wear properties of fretting of carbon fiber fabric composites presented obvious anisotropy. The friction dissipated energy and wear volume of the N orientation where the fibers are vertical and parallel to the contact surface are all less than that of the P orientation where the fibers are parallel to the contact surface. In MR, the damage circle radius is increased with increasing number of cycles and the damage circle radius of N orientation is smaller than that of P orientation.
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    Experimental Study on Discrete Element Simulation of Powder Injection Molding
    LIU Yu, LI Yi-min, XIA Qing-kun, HE Hao, HU You-hua
    2014, 0 (4): 85-88.   DOI: 10.3969/j.issn.1001-4381.2014.04.015
    Abstract ( 656 ( PDF (2449KB)( 217 Citation
    The discrete element granular model on powder injection molding was established. Powder was treated as granular model according with Newton Law and interaction each other rather than continuous phase, and viscous liquid bridge was simulated by parallel bonding model. Wax-based binder and 17-4ph stainless steel powder were mixed and injection molded, so the standard tensile samples and bending samples were obtained. The uniaxial tension and three-point bending tests were carried on. The results of tests and discrete element simulation were compared and analyzed. The results show that the crack morphology, position, force-displacement curves are consistent. The reliability of discrete element is verified and the micro parameters of discrete element granular model are checked.
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    Preparation of Polystyrene/CdS Core-shell Composite Nanoparticles by Hydrothermal Method
    SUN Guan-hua, QIU Shi, ZHENG Jing-tang
    2014, 0 (4): 89-94.   DOI: 10.3969/j.issn.1001-4381.2014.04.016
    Abstract ( 1041 ( PDF (2431KB)( 448 Citation
    Polystyrene/CdS core-shell structure nanoparticles were synthesized by hydrothermal method. The polyvinyl pyrrolidone was introduced to improve the affinity between CdS nanoparticles and the polymeric matrix,subsequently preventing the aggregation of polystyrene microspheres. The optimized preparation conditions was explored by changing the hydrothermal time and Cd2+ to S2- molar ratio. The morphology, composition, microstructure and size of the nanoparticles were investigated by the SEM, TEM, XRD and FT-IR method. The results show that polystyrene/CdS nanoparticles by hydrothermal method have abvious core-shell structure, the core of the nanocapsules was typically spherical structure with 260nm diameter,and the uniform shell thickness of the nanocapsules is ranging from 10nm to 50nm, as well as high catalytic performance.
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    Progress in Research on Polymer Nano/Sub-micro Structures by Injection Molding
    ZHOU Ming-yong, JIANG Bing-yan, LU Li-jun, ZHANG Lu, CHEN Lei
    2014, 0 (4): 95-100.   DOI: 10.3969/j.issn.1001-4381.2014.04.017
    Abstract ( 935 ( PDF (1451KB)( 440 Citation
    The recent research development on polymer nano/sub-micro structures by injection molding was reviewed. The influences of such conditions as processing materials, mold materials and the molding process on the replication quality of nano/sub-micro structures were analyzed in detail. In addition, the manufacturing technology of mold inserts and aided techniques were also discussed. Finally, the issues in the nano injection molding and forecast to the future developments of this research field were investigated.
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