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      20 April 2013, Volume 0 Issue 4 Previous Issue    Next Issue
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    Investigation on Particles Reinforced Titanium Matrix Composite Coating Fabricated by Cold Spraying
    HUANG Chun-jie, LI Wen-ya, YU Min, LIAO Han-lin
    2013, 0 (4): 1-5,11.   DOI: 10.3969/j.issn.1001-4381.2013.04.001
    Abstract ( 951 ( PDF (2076KB)( 460 Citation
    SiC particles reinforced Ti matrix composite(PRTMC) was prepared by cold spraying,using titanium metallic matrix blended with reinforcement of irregular SiC powder as feedstock. The effect of SiC reinforcement on the microstructure and microhardness of the composite coating was studied. The results show that two distinguishable regions exist in the deposited composite coating: the outer region and the inner region. The outer region presents a porous microstructure, while the inner region has a dense microstructure. The porosity of the coating becomes smaller with the increasing of the depth from the surface towards the boundary. The volume fraction of SiC particles in the deposited coating is 10% compared to that of 30% in the feedstock. Furthermore, the addition of SiC particles can effectively reduce the coating porosity, and greatly increases the microhardness of cold-sprayed coating from (72?28)HV0.1 to (125?17.75)HV0.3.
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    Microstructure and Properties of Ultra-high Strength Ferrite-martensite Dual Phase Steel Tested Under Dynamic Tensile Conditions
    DAI Qi-feng, SONG Ren-bo, GUAN Xiao-xia
    2013, 0 (4): 6-11.   DOI: 10.3969/j.issn.1001-4381.2013.04.002
    Abstract ( 840 ( PDF (3522KB)( 429 Citation
    Two groups of experimental dual phase (DP) steels with the same ferrite grain size and different martensite volume fraction were obtained through performing the experiment of step quenching (SQ) continuous annealing. The quasi-static tensile experiment and the dynamic tensile experiment for the two groups of DP steels were carried out at room temperature using universal testing machine CMT-4105 at strain rate of 10-4s-1 and split Hopkinson tensile bar (SHTB) at strain rate of 500s-1 and 2250s-1, respectively. Effect of high strain rate deformation on microstructure and properties of ultra-high strength ferrite-martensite dual phase steel tested under dynamic tensile conditions was investigated using the dynamic factor and Feret ratio quantitative analysis method. The results show that strain rate effect plays a role of strengthening for dynamic deformation behavior of dual phase steel; that strain rate sensitivity of dual phase steel increases with the decreasing of martensite volume fraction; that strain rate sensitivity of proof strength of ultra-high strength dual phase steels is greater than that of tensile strength. Adiabatic temperature rise which is calculated of the two kind of dual phase steels under 2250s-1 strain rate dynamic tensile conditions was 98K and 89K, and it counteracts the strengthening effect of strain rate.
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    Effect of Vacuum Pre-oxidation on Microstructure and Hot Corrosion Behavior of CoNiCrAlY Coating Prepared by Cold Spray
    ZHANG Lin-wei, WANG Lu, WANG Quan-sheng, NING Xian-jin
    2013, 0 (4): 12-16.   DOI: 10.3969/j.issn.1001-4381.2013.04.003
    Abstract ( 851 ( PDF (2026KB)( 495 Citation
    CoNiCrAlY coatings were prepared by cold spray process. After deposition, the pre-oxidation of the coating was performed by vacuum heat-treatment. The microstructure and phase constituent of coating were characterized by XRD, FE-SEM and TEM. The corrosion behavior and mechanisms of as-sprayed and pre-oxidized coatings in molten 75%Na2SO4+25%NaCl (mass fraction, the same below) at 900℃ were also studied. The results show that the as-sprayed coating presents a nanocrystalline structure with low porosity (less than 0.28% volume fraction) and low oxygen content (0.12%). Vacuum pre-oxidation treatment improves the bonding status of particle interface and forms a continuous, uniform and dense α-Al2O3 layer, with an average thickness of 0.26μm. As-sprayed and pre-oxidized coatings can protect the substrate from hot corrosion due to the formation of the continuous and dense α-Al2O3 layer. Moreover, the vacuum pre-oxidation treatment can alleviate the diffusion of S and Cl into coating and thus lead to an increase of one time in the hot corrosion resistance than the as-sprayed coatings.
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    Crystallization and Dielectric Properties of Carbon Nanofiber/High-density Polyethylene Composites
    SUN Li-li, ZHONG Yan-li
    2013, 0 (4): 17-22.   DOI: 10.3969/j.issn.1001-4381.2013.04.004
    Abstract ( 830 ( PDF (3086KB)( 338 Citation
    An attractive type of nanofiller-carbon nanofiber (CNF) was used to modify high-density polyethylene (HDPE), in which the nanocomposites with 1%-20% CNFs were prepared via a two-step process including melt mixing and hot press. The crystallization and dielectric properties of CNF/HDPE composites, as well as the dispersion of CNFs, were investigated . The results showed that CNFs were well dispersed in HDPE. It was also demonstrated that the crystallinity and crystal size of HDPE were influenced by the introduction of CNFs. The (110) planes of HDPE was also enhanced as proved with the increased intensity of the characteristic peak. In addition, the dielectric constant of nanocomposites was dramatically improved with higher CNF contents. The highest dielectric constant, 580 at 103Hz, was achieved with 20% CNFs, which was about 150 times higher than that of pure HDPE. Simultaneously, the dielectric constant of nanocomposites showed high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The AC conductivity of nanocomposites was also greatly affected by CNF,the characteristic of direct conductivity was obviously exhibited with the CNF concentration higher than 10%.
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    Investigation on Critical Strain of Dynamic Recrystallization for 7A04 Aluminum Alloy
    LI Dong-qin, XU Lei, HUANG Xing-min, DAI Guang-ze
    2013, 0 (4): 23-27.   DOI: 10.3969/j.issn.1001-4381.2013.04.005
    Abstract ( 996 ( PDF (1967KB)( 296 Citation
    The thermal simulation compression tests of 7A04 aluminum alloy were conducted at 350-450℃ with the strain rate of 0.01-10s-1 on the Gleeble thermal simulation test machine. Based on hyperbolic sine relations of peak stress,the thermal deformation activate energy Q of 7A04 aluminum alloy was determined. Based on Sellars model and work hardening rate θ, the critical strain constitutive model of dynamic recrystallization was established. The results show that comparisons between the simulated and experimental results are satisfactory and the constitutive model of critical strain could be used for indicating the beginning of dynamic recrystallization for 7A04 aluminum alloy.
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    Influence of Oxygen/Fuel In-gun Ratio on Oxidation Resistance of CoCrAlYTa Coating Prepared by Detonation Gun Spraying
    GAO Jun-guo, LU Feng, WANG Chang-liang, GUO Meng-qiu, CUI Yong-jing
    2013, 0 (4): 28-33.   DOI: 10.3969/j.issn.1001-4381.2013.04.006
    Abstract ( 876 ( PDF (2737KB)( 270 Citation
    CoCrAlYTa coatings were prepared by means of detonation gun spraying.The influence of oxygen/fuel in-gun ratio on the structure and oxidation resistance of the as-prepared coatings was investigated by SEM, EDS, XRD and high-temperature oxidation test. The results revealed that the detonation temperature and bombardment velocity increased with the increased of oxygen/fuel in-gun ratio, which induced the transformation of coating structure from uniform structure to lamellar structure and the decreased of the coating porosity. Meanwhile, the continuous oxide scale was prone to being formed earlier if the coating was more compactness, which decreased the parabolic rate constant kP of the coating. The critical concentration of Al element in the coating to form Al2O3 declined consequently and the selective oxidation of Al was promoted. The formed Al2O3 layer can further suppress the diffusion of oxygen into the coating and result in the enhancement of oxidation resistance with the increase of oxygen/fuel in-gun ratio.
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    Numerical Simulation of Residual Stresses for Aluminum Alloy Pipe Incorporating Metallurgical Phase Transformation
    LIAO Juan, LING Ze-min, PENG Xiao-yang
    2013, 0 (4): 34-38.   DOI: 10.3969/j.issn.1001-4381.2013.04.007
    Abstract ( 987 ( PDF (1811KB)( 363 Citation
    Based on the butt joint of thin-walled aluminum alloy pipe, according to the practical situation, three-dimensional thermal, metallurgical and mechanical finite element model was established. The temperature field during welding process, axial and hoop residual stresses of circumferential welds incorporating metallurgical phase transformation were simulated by using SYSWELD software. The model was accurately predict the welding residual stresses and the results coincided with experiment. In addition, the effects of pipe diameter on residual stresses were investigated. The results showed that affected metallurgical phase transformation on the maximum axial tensile stress and maximum hoop tensile stress and compressive stress, and models with metallurgical phase transformation can simulate axial and hoop stresses more accurately; considering phase transformation, the residual stresses increased with increasing the radius, and residual stresses with different radii have a similar trend.
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    Effect of Water on Cellular Structure and Properties of Rigid Polyurethane-imide Foams
    AN Man, CHEN Xing-gang, HOU Gui-xiang, SANG Xiao-ming
    2013, 0 (4): 39-44.   DOI: 10.3969/j.issn.1001-4381.2013.04.008
    Abstract ( 761 ( PDF (2402KB)( 404 Citation
    PI prepolymerization method was adopted to synthesize rigid polyurethane-imide foams. The effect of content of water on the density, surface chalking degree and mechanical properties was analyzed. The relationship between the mechanical property and density was established following the power law. In addition, the cellular structure was observed using stereomicroscope and polarizing microscope. The results showed that,with the increased content of water, the density, compressive strength,compressive modulus, impact strength and cell edge thickness of rigid polyurethane-imide foams decreased,and average cell diameter and surface chalking degree of foams increased. The density exponent value was calculated as 1.78, 1.55 and 0.72 for compressive strength, compressive modulus and impact strength, respectively, for polyurethane-imide foams.
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    Properties of High Speed Steel SFT15 Prepared by Twin-scanning Spray Forming
    ZHANG Yong, LI Zhou, YUAN Hua, XU Wen-yong, ZHANG Guo-qing, FU Shu-hong, WANG Tao
    2013, 0 (4): 45-49.   DOI: 10.3969/j.issn.1001-4381.2013.04.009
    Abstract ( 975 ( PDF (2553KB)( 334 Citation
    The spray forming high speed steel SFT15 was manufactured by twin-scanning spray forming equipment. The volume density, some mechanical properties and microstructure of high speed steel (HSS) SFT15 prepared by twin-scanning spray forming were researched. The results indicated that the average volume density of SFT15 deposit was 8.2g/cm3,which was 99.3% of theoretical density. The high-quality perform of HSS SFT15 exhibited high-density, refined grains and segregation-free macrostructure. And the hot forge can improve the mechanical properties of SFT15 remarkably, the hardness of SFT15 can reach HRC67.6 and bending strengths exceeded 4200MPa. By means of scanning electron microscope (SEM), the results indicated that the structure of HSS SFT15 was constituted by fine carbide distributed non-segregately.
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    Property and Process of Cold-rolled Steel Zirconia-silica Coating
    YANG Yu-chang, WANG Feng, HU Jian-qing, TU Wei-ping
    2013, 0 (4): 50-55,62.   DOI: 10.3969/j.issn.1001-4381.2013.04.010
    Abstract ( 882 ( PDF (2071KB)( 305 Citation
    A thin top layer composed of zirconia and organosilicone was prepared on the cold-rolled steel through condensation reactions by sol-gel method, using sodium fluozirconate and 1,2-bis(trimethoxysilyl)ethane as precursor. The anti-corrosion property of the coating was measured by electro-chemical testing methods and CuSO4 dripping experiment. The functional groups, morphology and composition were investigated by SEM, FTIR and XPS methods, respectively. The results indicate that, compared to the pure silane coating, the corrosion current density of the composite coating is much lower and the polarization resistance increases significantly, and the morphology does not change essentially after the corrosion. The XPS analysis reveals that Si-O-Zr bond was formed on the surface. A new structural model is gave after investigating the mechanism of bonding and anti-corrosion of the zirconium salt on the surface.
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    Syntheses and Characterization of Bio-hydroxyapatite/Poly(Amino Acid) Copolymer Composite
    JIANG Jia-chun, LYU Guo-yu, YAN Yong-gang, WU Deng-xue, LIU Shao-ying
    2013, 0 (4): 56-62.   DOI: 10.3969/j.issn.1001-4381.2013.04.011
    Abstract ( 898 ( PDF (2570KB)( 215 Citation
    A novel synthetic materials of bio-hydroxyapatite/poly(amino acid) copolymer composite for bone repair was prepared by in-situ polymerization. The structure and thermal properties were characterized by nuclear magnetic resonance (1HNMR), infrared spectrometer (IR), X-ray diffractmeter (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and differential scanning calorimeter (DSC); the compressive and flexural strength of the composite containing different BHA contents were investigated during degradability. The results indicated that the BHA particles distributed uniformly in the composite. The IR and XPS results showed that chemical bond was present between inorganic (BHA) and the organic (PAA). With 30%(mass fraction)BHA, the compressive strength of the composite enhanced with the introduction of BHA and reached 141.02MPa, and flexural strength was 86.32MPa,which is in the range of natural bone mechanical strength. The composite exhibited excellent degradability and its degradability enhanced with the increased of BHA content, and exhibited good biomechanical strength.
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    Novel Cyanate Ester Resin Composites for Microelectrical Packaging
    XUE Jie, YE Ju-hua, GUAN Qing-bao, LIU Ping, LIANG Guo-zheng
    2013, 0 (4): 63-67.   DOI: 10.3969/j.issn.1001-4381.2013.04.012
    Abstract ( 803 ( PDF (1450KB)( 237 Citation
    Three composites based on CE resin, aluminum nitride (AlN), nano AlN (n-AlN) and silicon dioxide (SiO2), and silane coupling agent (KH560) modified AlN and SiO2,coded as AlN/CE, n-AlN/CE, AlN-SiO2/CE and AlN(KH560)-SiO2(KH560)/CE composite, respectively, were prepared. The influences of the sort,size and surface nature of fillers on the thermal conductivity and dielectric properties of composites were investigated in detail. The results show that properties of fillers have great influence on the thermal conductivity of composites. When CE resin was filled by n-AlN and AlN,the resultant composites increased thermal conductivity due to the close arrangement.The composite with a higher content of AlN had higher dielectric constant.But when SiO2 was used to replace AlN,the increasement of dielectric constant was reduced.
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    Continuous Cooling Transformation of CLAM Steel in Heat Affected Zone
    JIANG Zhi-zhong, HUANG Ji-hua, HU Jie, CHEN Shu-hai
    2013, 0 (4): 68-73.   DOI: 10.3969/j.issn.1001-4381.2013.04.013
    Abstract ( 936 ( PDF (3241KB)( 325 Citation
    By means of the physical simulation, the coarse grained zone in heat affected zone (CGHAZ) of CLAM steel during cooling process in the welding thermal cycles was conducted by using of the Gleeble1500 simulator. The effects of cooling rates(ωc)on microstructure transformation and Vickers hardness were investigated through microscopic observations, hardness tests as well as thermodynamic calculation with Thermo-calc software, and the SH-CCT diagram of the CGHAZ for CLAM steel was finally established. The results showed that the SH-CCT diagram exhibited only two transformation regions, i.e. low-temperature lath martensite (LM) region and high-temperature proeutectic ferrite (α-ferrite) region. 0.25℃/s was the critical cooling rate for phase transformation from supercooled austenite to full martensite. When the ωc>0.25℃/s,the microstructure appearances of CGHAZ had no significant changes and consists of lath martensite and a small amount of δ ferrite within this range, the occurrence of δ ferrite was attributed to incomplete δ→γ transformation in the high temperature stage. When the ωc<0.25℃/s, the CGHAZ showed dual phase of α-ferrite and lath martensite because of the γ→α transformation. The content of α-ferrite increased with the decreased cooling rate. When the ωc=0.04℃/s, the microstructure of CGHAZ was completely transformed to α-ferrite and carbides.
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    3D EBSD Analysis of Morphology and Habit Plane for Lath Martensite
    WANG Hui-zhen, YANG Ping, MAO Wei-min
    2013, 0 (4): 74-80.   DOI: 10.3969/j.issn.1001-4381.2013.04.014
    Abstract ( 1382 ( PDF (6079KB)( 812 Citation
    The 3D morphology of lath martensite was reconstructed, and its habit plane was analyzed in high manganese steels,using a system of 3D EBSD-FIB (three dimensional electron backscatter diffraction- focused ion beam). The results show that the surfaces of thermally-induced lath martensite are straight and close to martensitic {110}α, and the habit planes are close to austenitic {225}γ; the directions of initial nucleation and the later growth are along {225}γ plane. The surfaces and the habit planes of deformation-induced lath martensite are on the verge of {021}α and {225}γ, respectively; the nucleation and early growth are along {225}γ, while later growth planes are changed to {111}γ; because of the external stress, its surfaces are flexuous, and the degree of the deviations of the ones with {225}γ-{111}γ is various with nucleation time.
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    Effects of Ca and La on Microstructures and Creep Properties of Mg-5Sn-2Si Alloy
    ZHANG Guo, DU Jun, LI Wen-fang, DOU Qi, CAI Tian-xiang
    2013, 0 (4): 81-84.   DOI: 10.3969/j.issn.1001-4381.2013.04.015
    Abstract ( 779 ( PDF (1681KB)( 328 Citation
    The Mg-5Sn-2Si alloy was modified by the Mg-20%Ca(mass fraction, the same below)and Mg-20%La master alloys separately. The modifying effects of Ca and La on the Mg2Si phase were investigated, and high temperature creep testing was conducted as well. The results showed that Ca and La had a good modifying effects on Mg2Si phase, granuliform primary Mg2Si phase disappeared and the morphology and distribution of the coarse dendritic Mg2Si were obviously affected and new flower-like CaMgSi and rod-like La5Si4 compounds were found in the alloys. The creep rate of the alloy with the modifying of Ca and La decreased significantly, under 250℃,60MPa stress conditions. The steady creep rate of Mg-5Sn-2Si-2Ca and Mg-5Sn-2Si-2La alloys decreased to 1/48 and 1/28 respectively, compared with the unmodified alloy. The reason for the increase of the creep resistance may have to do with that the Mg2Si phase was refined as well as dislocation slipping and grain boundary sliding were much more blocked after the new compounds generated.
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    Effect of Electric Field Induced on Property of Unsaturated Polyester Resin/Carbon Fibre/Nanosize Carbon Black Composite
    ZHAO Bo, LI Xiao-gang, GAO Jin, DU Cui-wei
    2013, 0 (4): 85-91.   DOI: 10.3969/j.issn.1001-4381.2013.04.016
    Abstract ( 921 ( PDF (6008KB)( 362 Citation
    A type of composite was made of unsaturated polyester resin(UPR), carbon fibre(CF), and nanosize carbon black(CB). The electrical and basic mechanical properties of the composite with electric field induced and conventional molding was compared and analyzed. The results showed that the conductivity of composite was anisotropic and could be enhanced when the filling amount was appropriate with 0.3V/μm direct current (DC) electric field induced. The best CB filling amount was 0.5phr. At that time, the volume resistivity of composite with CF filling amount was 3,6,9phr reduced 46.8%,29.0%,12.5% at axial direction, and 28.6%,18.8%,8.3% at normal direction of electric field line. Meanwhile, the basic mechanical properties of composite was not changed by electric field induced,and maintained substantially constant.
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    Research Status and Development Trend of Bulk Nano/Micro-crystalline Composite Metallic Materials
    WANG Hong-ding, LA Pei-qing, SHI Ting, WEI Yu-peng, LU Xue-feng
    2013, 0 (4): 92-96.   DOI: 10.3969/j.issn.1001-4381.2013.04.017
    Abstract ( 909 ( PDF (589KB)( 368 Citation
    This paper reviewed the development and microstructure design of bulk nano/micro-crystalline composite metallic materials, and its fabrication methods and deformation mechanisms.The material systems and the advantages and disadvantages of these methods were discussed. And it is indicated that the nano/micro-crystalline composite metallic materials will focus on developing the new and superior fabrication method, and finding the optimum microstructure parameters to prepare nano/micro-crystalline composite metallic materials which obtain both high strength and good uniform ductility.
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