Jun 2007, Volume 1 Issue 2

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  • WANG Guangchun, ZHAO Guoqun, GUAN Jing
    A microstructure optimization design method of the forging process is proposed. The optimization goal is the fine grain size and homogeneous grain distribution. The optimization object is the forging process parameters and the shape of the preform die. The grain size sub-objective function, the forgings shape sub-objective function and the whole objective function including the shape and the grain size are established, respectively. The detailed optimization steps are given. The microstructure optimization program is developed using the micro-genetic algorithm and the finite element method. Then, the upsetting process of the cylindrical billet is analyzed using a self-developed program. The forging parameters and the shape of preform die of the upsetting process are optimized respectively. The fine size and homogenous distribution of the grain can be achieved by controlling the shape of the preform die and improving the friction condition.
  • LU Li, ZHAO Haiyan, CAI Zhipeng, CUI Xiaofang
    Defects such as pores influence the fatigue life of electron beam-welded aluminum alloy joints. In this paper, the influences of pore size and position on the fatigue life of aluminum overlap joint are studied. A finite element model (FEM), combined with experimental data, is established to evaluate the fatigue life of overlap joints. By employing this FE model, the effects of pore size and position on fatigue lives of overlap joints are investigated and discussed. From the present study, when pore position is closer to the weld bead tip or the faying surface, the fatigue life decreases. Also, there is a critical size for the pore; when the pore size is larger than the critical value, the fatigue strength decreases sharply.
  • GAO Jinqiang, WU Chuansong, HU Jiakun
    A real-time monitoring system based on through-the-arc sensing is developed for detecting abnormal conditions in gas metal arc welding. The transient signals of welding voltage and current during the welding process are sampled and processed by statistical analysis methods. It is found that three statistical parameters (the standard deviation, variance, and kurtosis of welding current) show obvious variations during the step disturbance, which is intentionally introduced into the T-joint test pieces by cutting a gap in the vertical plane. A Fuzzy Kohonen clustering network (FKCN) is put forward to monitor the abnormal conditions in real-time. Ten robotic welding experiments are conducted to verify the real-time monitoring system. It is found that the correct identification rate is above 90%.
  • JIAO Yanpeng, LIU Zonghua, ZHOU Changren, CUI Fuzhai
    The biomimetic apatite coating process was adopted to modify poly(L-lactide) (PLLA) surfaces with osteoblasts-like cell compatibility. The apatite coating was formed on the pre-hydrolyzed PLLA film and scaffold surfaces by incubating in simulated body fluid (SBF). Scanning electron microscopy and energy dispersive X-ray analyzer were utilized to characterize the composition and the structure of the apatite coating. The cytocompatibility of the modified PLLA films was investigated by testing osteoblast-like attachment, proliferation, alkaline phosphatase (ALP) activity, and cell cycle. Subsequently, the modified PLLA scaffolds were co-cultured with the osteoblasts-like in vitro and subcutaneously implanted into nude mice. The experimental results showed that the formed apatite had a nano-sized particle and matrix configuration. The surface modification of PLLA with apatite coating significantly promoted osteoblast-like compatibility. After a four-week culture in vivo, no significant inflammatory signs were observed in the implanted regions and osteoblast-like congeries with bone-like structure began to form in the scaffolds. The positive results of this study suggest a good way to produce desirable PLLA biomaterials for bone tissue engineering.
  • LIU Tong, TANG Huiqin, ZHAO Jie, LI Dejun, LI Ruying, SUN Xueliang
    A Cu layer was coated on carbon nanotubes (CNTs) by ion beam-assisted deposition (IBAD). Standard agar dilution method was used to evaluate the bactericidal rate against E. coli and S. aureus bacteria. The structure and chemical states of the Cu-coated CNTs were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the Cu-coated CNTs possess a very high bactericidal rate. In comparison with the Cu-coated pyrolytic carbon sample, the Cu-coated CNTs show much stronger bactericidal property.
  • ZHAO Yanchao, CHENG Shujun, CHEN Jianding
    In this experiment we prepared the copolymer of L-lactide (L-LA) and (3s)-[(benzyloxycarbonyl) methyl] morpholine-2,5-dione (BMD) using tin(II)-octanoate initiated ring-opening copolymerization. The maximum relative number-average molecular weight (M n) of copolymer was over 8.0?104. The degradation study proceeded in vitro and poly(L-lactide-co-glycollide) used as the control sample. Changes in mass and molecular weight were studied during the immersion in buffer solutions [phosphate-buffered saline solution (PBS), pH = 7.4] at 37?C. The hydrolytic degradation of both the morpholine-2,5-dione derivative copolymer and the control sample were completed in 3 months. A palladium on charcoal catalyst [Pd/C (5%)] was used as the catalyzer for hydrogenolysis. 1H-NMR (nuclear magnetic resonance) analysis and gel permeation chromatography (GPC) were used to investigate the degree of the hydrogenolysis of the copolymer with different M n. The contact angle showed that the biodegradable copolymer had good hydrophilicity. These findings suggested that this copolymer would have a high potential application for pharmaceutical products.
  • JIN Chenggang, WU Xuemei, SHA Zhendong, ZHUGE Lanjian
    ZnO/SiC multilayer film has been fabricated on a Si (111) substrate with a silicon carbide (SiC) buffer layer using the RF (radio frequency)-magnetron technique with targets of a ceramic polycrystalline zinc oxide (ZnO) and a composite target of pure C plate with attached Si chips on the surface. The as-deposited films were annealed at a temperature range of 600 1000?C under nitrogen atmosphere. The structure and photoluminescence (PL) properties of the samples were measured using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and PL spectrophotometry. By increasing the annealing temperature to 800?C, it is found that all the ZnO peaks have the strongest intensities, and the crystallinity of ZnO is more consistent on the SiC buffer layer. Further increase of the annealing temperature allows the ZnO and SiC layers to penetrate one another, which makes the interface between ZnO and SiC layer become more and more complicated, thus reduces the crystallinities of ZnO and SiC. The PL properties of a ZnO/SiC multilayer are investigated in detail. It is discovered that the PL intensities of these bands reach their maximum after being annealed at 800?C. The PL peaks shift with an increase in the annealing temperature, which is due to the ZnO and SiC layers penetrating reciprocally. This makes the interface more impacted and complicated, which induces band structure deformation resulting from lattice deformation.
  • TIAN Zhen, WANG Meng, ZHANG Aiying, FENG Zengguo
    This paper describes a preliminary study on the synthesis of glycopeptide-based triblock copolymers and their aggregate behavior in water. Initially, a polypeptidebased triblock copolymer, poly(L-lysine)-b-poly(tetrahydrofuran)-b-poly(L-lysine) (PLL30-b-PTHF-b-PLL30), was synthesized by the ring-opening polymerization of ε-benzyloxycarbonyl-L-lysine N-carboxyanhydride using amine-terminated poly(tetrahydrofuran) as a macroinitiator in the fixed feed ratio, followed by the removal of the protecting group. The resulting copolymer then reacted with a varying amount of D-gluconolactone in the presence of dipropylethylamine to give the corresponding glycopeptide-based copolymers with high yields. This kind of amphiphilic sugar-containing triblock copolymer can self-assemble into nano-sized aggregates in water. The critical aggregation concentration (CAC) was determined in the range of around 10-6 M by fluorescence measurement. The spherical morphologies in 100 150 nm scale were also evidenced by transmission electron microscopy (TEM) measurements. They show potential as carriers for drug controlled delivery and templates for biomimetic mineralization.
  • LI Xue, YIN Zhimin, PAN Qinglin, JIANG Feng, NIE Bo, ZHONG Li
    The fatigue crack growth rate, fracture toughness and fatigue S-N curve of 2124-T851 aluminum alloy at high cycle fatigue condition were measured and fatigue fracture process and fractography were studied using optical microscopy (OM), X-ray diffraction (XRD) technique, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that at room temperature and R = 0.1 conditions, the characteristics of fatigue fracture could be observed. Under those conditions, the fatigue strength and the fracture toughness of a 2124-T851 thick plate is 243 MPa and 29.64 MPa · m1/2, respectively. At high cycle fatigue condition, the higher the stress amplitude, the wider the space between fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area, and the greater the ratio between the intermittent fracture area and the whole fracture area.
  • SUN Liang, ZHANG Qingchuan, JIANG Huifeng
    The solute concentration and precipitated phase content in alloys were altered by solution treatment (ST) at different temperatures. A series of serrated load curves was obtained in tensile tests at a constant applied strain rate. The influences of solute concentration and precipitated phase content on dislocation movement were analyzed with tensile test results, and the micro-mechanism of the Portevin-Le Chatelier (PLC) effect is discussed in this paper. In the tests, when ST temperature was reduced from 500vH, the amplitude of serrated flow decreased. It reached the minimum when ST temperature was reduced to 300vH. On the other hand, the amplitude of serrated flow increased with ST temperature decreasing from 300 to 100vH. Experimental results show that when ST temperature is higher than 300vH, solute concentration is a governing factor to PLC effect; whereas when ST temperature is lower than 300vH, the precipitated phase content significantly affects the PLC effect.
  • PENG Jiangying, YANG Junyou, SONG Xinli, CHEN Yuehua, BAO Siqian, ZHANG Tongjun
    Mechanical alloying and preparation of Fesubstituted CoSb3-based skutterudite Co4 xFexSb12 (x"d1) were studied. All the compositions showed similar kinetics in mechanical alloying, where the skutterudite phase was kinetically more favorable than CoSb2 phase initially. Then the latter became the strongest phase when milling time was increased. A single phase skutterudite structure could not be obtained via mechanical alloying. Hot pressing on powders milled for 10 hours yielded mostly skutterudite phase as well as minor residual Sb impurity, and single phase skutterudite compounds were finally obtained for Co4 xFexSb12 (x"d0.65) after annealing at 650?C for 48 hours. The maximal solubility for Fe substitution seemed to be reached at x = 0.65.
  • CHU Ke, JIA Chengchang, YIN Fazhang, MEI Xuezhen, QU Xuanhui
    In this paper, a SiCP preform was prepared by Powder Injection Molding (PIM), and the melting aluminum was injected into the SiCP preform by the pressure infiltration method to manufacture an electronic package box of SiCP (65%)/Al composites. SiCP (65%)/Al composite prepared by pressure infiltration has full density and a homogeneous microstructure. The relative density of the composite is higher than 99%, the thermal expansion coefficient and thermal conductivity of the composite are 8.0?10 6/K and nearly 130 W/(m °K) at room temperature, respectively, which meet the requirements of electronic packaging.
  • XU Shubo, ZHAO Guoqun, WU Xin, MA Xinwu, GUAN Yanjin
    Equal channel angular pressing (ECAP) has the capability of producing ultra fine-grained (UFG) materials bellow the dimension of 1 μm. At present, it is one of the most important methods to get bulk UFG materials. Multi-pass ECAP processes for round workpieces are investigated by using numerical simulations and experimental studies in this paper. The deformation mechanism of ECAP for grain refinement is obtained. Three processing routes A, B and C are simulated in order to study the influence of the processing routes to the deformation uniformity of the workpiece. The finite element (FE) analysis results of the multi-pass ECAP process show that the different processing routes result in the different deformation distributions. The grain in the workpiece is refined obviously after multi-pass pressing. The microstructures of the processed material are more different than that of the microstructure of the annealing initial equiaxed grains. The microstructure evolution of the workpiece can be changed via different processing routes. It is found that route B can get a high angle grain boundaries distribution in the workpiece than other routes. The results of the analysis show that the process of grain refinement can be described as a continuous dynamic recovery and recrystallization. The microstructure evolutions of the grain refinement mechanisms and micro-structural characteristics for different multi-pass ECAP processing routes are verified by using OM (optical model) and TEM (transmission electron microscope) analysis. In addition, the experimental microstructure results are also consistent with FE analysis results.
  • GUAN Jianjun, CHEN Huaining
    This paper focuses on the simulation of welding residual stresses and the action of explosion shock waves on welding residual stresses. Firstly, the distributions of welding temperature field and residual stress on a butt joint were numerically simulated with the sequentially coupled method. Secondly, the effect of explosion shock waves, produced by plastic strip-like explosive, on welding residual stress distribution was predicted with coupled Lagrange-ALE algorithm. It was implicated that explosion treatment could effectively reduce welding residual stresses. The simulation work lays a foundation for the further research on the rule of explosion treatment s effect on welding residual stresses and the factors that may influence it.
  • GUO Shaoqing, LI Xiaohong
    In order to predict the propensity of a superalloy to heat-affected-zone (HAZ) liquation cracking, Visual FORTRAN procedures were developed based on a heat transfer and mass diffusion model and the constitutional liquation of precipitate (NbC) at grain boundaries was simulated numerically. The results show that with the increase in the rate of welding thermal cycle, the solid dissolution of precipitate prior to liquation decreases and the thickness of liquid film produced by constitutional liquation increases. Higher heating rate inhibits the further melting of adjacent matrix and the solidification of liquid by liquid-to-γ mode in the subsequent thermal cycle. As a result, the residual liquid film still maintains a great thickness at the moment when temperature is down to the eutectic point, which will promote HAZ micro-fissuring. Finally, hot ductility tests on a low-expansion superalloy were performed to verify indirectly the conclusions drawn from the numerical simulation.
  • WANG Aijuan, LU Yupeng, CHEN Chuanzhong, SUN Ruixue
    Two kinds of hydroxyapatite microspheres were prepared using an ultrasonic atomization method. The surface morphology, phase composition, size distribution and specific surface area were determined by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry and laser diffraction particle size analysis, respectively. The results indicate that the hydroxyapatite microspheres are composed of nanosized crystals and have porous surface morphology. The specific surface areas are different before sintering, and have a slight difference after sintering. The size distribution of the microspheres added with Lopon 885 is narrow and the average size is smaller than those fabricated without the addition of Lopon 885. Besides, the impurity phase, tetracalcium phosphate, appeared during ultrasonic atomizing procedure, and can be completely removed after sintering at 650vH for 1 h.
  • WANG Juan, LI Yajiang, XIA Chunzhi
    Fe3Al intermetallics and Q235 steel are bonded using vacuum diffusion bonding technology. The interfacial shear strength was measured and the stress of Fe3Al/Q235 diffusion bonded joint was analyzed using finite element analysis (FEA). The results indicate that interfacial shear strength increases from 39.9 to 112.3 MPa with the enhancement of heating temperature from 1000 to 1060vH. Also, shear fracture has more characteristics of cleavage fracture. The farther from the central axis of the interface, the larger the stress is, and the maximum stress appears on the surface of the joint. The maximum stress increases with the heating enhancement and increase of material thickness. When the thickness reaches a critical value (6 mm) and then increases, the stress increases slightly and even to a stable value.
  • YANG Shanglei, XUE Xiaohuai, LOU Songnian, LU Fenggui
    A new electron beam (EB) control system was developed in a general vacuum EB machine by equipping it with an industrial control computer, programmable logic control (PLC), deflection coil, data acquisition card, power amplifier, etc. In this control system, the scanning track and energy distribution of the EB could be edited off-line, adjusted in real-time, and controlled on-line. Ti-Mo gradient material (GM) with high temperature resistance was fabricated using electron beam smelting (EBS) control. The smelting pro cesses include three steps such as preheating, smelting, and homogenizing. The results show that GM prepared by using smelting technology has fine appearance, and has good integrated interface with Ti alloy. The Mo and Ti elements are gradual diversification in the interface of the gradient material. The microstructure near the Ti alloy base metal is α+β basket-waver grain, and the microstructure near GM is single phase of β solid solution.
  • WANG Xuegang, YAN Fengjie, YAN Qian, LI Xingeng
    An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer (EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the mechanical properties of the joint are similar around the pipe.