Dec 2007, Volume 1 Issue 4

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  • YANG Ping
    Twinning plays important roles in HCP metals and those FCC metals with low stacking fault energy. The structural difference of two types of metals makes quite different contributions of twinning to plasticity. The variety of grain orientation in polycrystalline metals causes the inhomogeneous occurrence of twinning and further distinct transformation kinetics of twinning as strain increases and texture develops. This changes finally the work hardening behavior and mechanical properties. This paper reveals the dependency of twinning on grain orientation in an FCC TWIP (twinning induced plasticity) steel with high Mn content and in a magnesium alloy using electron-backscatter-diffraction (EBSD) technique, and analyzes the characteristics of twinning in the two types of metals by Schmid factor calculation. In addition, the relation of twinning and shear banding, as well as their influence on properties are discussed.
  • REN Huiping, WANG Haiyan, LIU Zongchang
    Microstructure evolution of Fe-1.18%Cu binary alloy during solution and aging at 550°C was investigated under a high-resolution electron microscope (HREM). In addition, the aging strengthening mechanism was investigated based on the precipitation strengthening theory. Results show that there were lots of Cu atom clusters in the ferrite matrix during solid solution and initial aging stage, and Cu-rich metastable Fe-Cu particles precipitate subsequently at the aging hardness peak. It is found that there were high-density dislocations and stacking fault substructure in the Cu clusters that forms the obstacle of the dislocation motion, which should be the dominant reason of strengthening in the Fe-Cu alloy.
  • MAO Weimin
    A potential, rapid and accurate technology to determine r value of deep drawing steel sheets was investigated. The amount of pole figure data which should be measured is reduced drastically because of the pole figure symmetry. The necessary pole figures data can be collected holistically by the X-ray area detectors, after which the volume fraction of the texture components in Gaussian forms is obtained. According to the volume fraction of the texture components, the r value of the steel sheets can be then calculated rapidly and accurately based on the reaction stress deformation model, while some other effecting factors beside texture are also included. The rapid and accurate determination technology overcomes the shortages of current technologies which emphasize either more on velocity or more on accuracy, and can be applied to the on-line r value determination of deep drawing steel sheet.
  • LI Juntao, ZHENG Yanjun, CUI Lishan
    Effects of severe deformation and heat treatment on the transformation behaviors of explosively welded duplex TiNi/TiNi shape memory alloys (SMAs) were investigated by the differential scanning calorimeter (DSC). The explosively welded duplex TiNi/TiNi plate of 0.7 mm in thickness was cold-rolled at room temperature to the extent of 60% reduction in thickness and then annealed at different temperatures (573–973 K) for different time (15 min–10 h). Low temperature (623–723 K) heat treatment led to amorphous crystallization. At higher temperature (873 K), the re-crystallization took place in the specimens. Analysis showed that the change of internal stresses is just the root cause of the change of transformation temperature. The relationships between the transformation behaviors and the heat treatment were discussed in the present report.
  • YAN Zhu, CUI Lishan, ZHENG Yanjun
    In this paper, differential scanning calorimeter (DSC) was used to study the effects of predeformation and plate thickness on the reverse martensitic transformation of explosively welded NiTi/NiTi alloy. Results showed that there was a constraint between Ni50.4Ti (NiTi-1) and Ni49.8Ti (NiTi-2), which led to that the thickness of NiTi-1 or NiTi-2 strongly affected the reverse martensitic transformation behavior because residual stress variations in thickness wound enable bias force to be built inside the composite. The DSC measurements showed that after deformation, the reverse martensitic transformation temperature of the composite was increased with the increasing thickness of NiTi-2. Also, the XRD results revealed that the microstructure of NiTi/NiTi alloy changed from B2 phase to B19  phase along the thickness direction.
  • LI Huiping, ZHAO Guoqun, HE Lianfang
    In this paper, some key technologies of computing the quenching temperature field are given. According to the characteristics of quenching process, a new method of computing phase-transformation latent heat is presented to ensure the computation accuracy of temperature. The phase-transform latent heat is regarded as the internal heat source because it can result in the rise of temperature in the process of cooling. A new method of self-control and adaptive time-step is presented in this paper. This method can be used to compute the time-step according to maximum and minimum difference values of the temperature field between the previous simulating step and the current simulating step. A finite element method (FEM) software for evaluating the temperature and the phase-transformation is developed by using the methods presented in this paper, the lump parameters method and fine mesh method. The experimental results or analytical values of two cases are used to check the accuracy of FEM simulation. The comparisons show that the simulation results of FEM software are consistent with experimental results or analytical values.
  • Aditya M. Vora
    The vibrational dynamics of three Ca-based non-crystalline alloys viz. Ca70Mg30, Ca70Zn30 and Ca60Al40 have been studied at room temperature in terms of the phonon eigen frequencies of longitudinal and transverse modes, employing three theoretical formulations given by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). Five local field correction functions viz. Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used for the first time in the present investigation to study the screening influence on the aforesaid properties. The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard s Law. Long wavelength limits of the phonon modes are used to investigate the elastic and thermal properties of the system. The low temperature specific heat is also calculated from the elastic limit of the phonon dispersion curves (PDCs). The present findings of the PDCs of Ca70Mg30 glass are found in fair agreement with available theoretical and experimental data.
  • JIANG Qi, QIAN Lan, YI Jing, ZHU Xiaotong, ZHAO Yong
    Boron carbide nanotubes (nano-fibers) was prepared by B powder and carbon nanotubes (CNTs) at high temperature in a vacuumed quartz tube. The morphology, microstructure, component and magnetic property of samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and magnetic property measurement system (MPMS) controller. The results showed that B-doping CNTs have great difference in the morphology and magnetic property from those of pristine CNTs.
  • CUI Sheng, SHEN Xiaodong, LIN Benlan, SHI Ruihua, CHEN Ping
    The objective of this paper was to prepare paclitaxel-loaded microspheres, a kind of target-orientation anticancer drug. The paclitaxel-loaded microspheres were prepared with magnetic Fe3O4 nanoparticles and taxol. The morphology was characterized by scanning electron microscopy (SEM), and the average size and the size distribution were determined by a laser-size distributing instrument. High performance liquid chromatography (HPLC) was used to measure the paclitaxel content. Experimental results indicated that the effective drug loading and the entrapment ratio of paclitaxel-loaded microspheres were 1.83% and 92.62%, respectively.
  • XU Li, HU Kun, JIAO Yanpeng, CUI Fuzhai, AI Hongbin
    The intention of this study was to surface modify the poly-L-lactic acid (PLLA) film and evaluate the effects of the surfaces on the growth of vascular smooth muscle cells (VSMCs) in vitro. Collagen and hyaluronic acid (HA) were utilized as polycation and polyanion in this study. Layer-by-layer (LBL) self-assembly technique was used to lead to the formation of multilayer moleculer on the poly-Llactic acid (PLLA) film surfaces. Collagen/HA layers was overcasted coating on the PLLA surface after the activation layers by poly-(ethyleneimine) (PEI). The structure and morphology of the multilayer molecular were examined by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrophotometer and atomic force microscope (AFM), respectively. The ATR-FTIR analysis illuminated the presence of collagen on the PLLA surface. The AFM results showed the multilayer appeared on PLLA surface. The VSMCs were adopted to evaluate the cyto-compatibility of the modified PLLA films. It was found that the viability of VSMCs on the modified PLLA films were greater than that on original PLLA films and tissue culture plastic after ten days culture (p<0.05). Scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) data also confirmed the homogeneous results. These data suggest that collagen/HA coat can be successfully adopted in the surface modification of PLLA film through LBL technique, and also can enhance its cell compatibility.
  • XIE Zhiguo, HOU Dandan, YE Lin, ZHANG Aiying, FENG Zengguo
    A kind of novel 3-D cross-linked supramolecular structured hydrogels has been fabricated via enzymatic oxidative coupling of polypseudorotaxanes (PPRs) derived from the self-assembly of α-cyclodextrins (α-CDs) with 3-arm p-hydroxyphenylpropionate terminated PEG (3-HPPP) as a macromer by using horseradish peroxidase (HRP)/H2O2 catalytic system. The enzymatic cross-linking of the macromer or PPRs made with a smaller amount of α-CDs was found to be much faster than that by ordinary chemical pathways, showing the promise to be used as the surgical adhesive and sealant which are needed to rapidly function in vivo. The gelation time was highly extended and the gel content was considerably decreased by increasing the α-CDs to macromer feeding molar ratio. Thereby these hydrogels exhibited a decreasing trend in dynamical mechanical properties with increasing the amount of α-CDs in regard to the blank hydrogel made without α-CD addition.
  • REN Yibin, HUANG Jingjing, ZHANG Bingchun, YANG Ke
    Magnesium alloys are potential to be developed as a new type of biodegradable implant material by use of their active corrosion behavior. Both in vitro and in vivo biodegradation properties of an AZ31B magnesium alloy were investigated in this work. The results showed that AZ31B alloy has a proper degradation rate and much lower hydrogen release in Hank s solution, with a degradation rate of about 0.3 mm/year and hydrogen release below 0.15 mL/cm2. The animal implantation test showed that the AZ31B alloy could slowly biodegrade in femur of the rabbit and form calcium phosphate around the alloy sample, with the Ca/P ratio close to the natural bone.
  • HUANG Jingjing, REN Yibin, ZHANG Bingchun, YANG Ke, JIANG Yue
    In order to investigate the in vivo behavior of pure magnesium and AZ31B and the influence of mineralization induction ability, sample rods were implanted intramedullary into the femora of rabbits. After one and nine weeks, six animals from each group were sacrificed, respectively. Undecalcified cross-sections of implant were performed to observe bone-implant by scanning electron microscopy (SEM) and energy dispersive spectromicroscopy (EDS). The SEM/EDS evaluation showed that there is a thin layer of bone around magnesium and its alloy after nine-week implantation. The results further showed that the aluminum-zinc containing magnesium alloys AZ31B provided a slower degradation rate in vivo than the pure magnesium. At the locations where magnesium was resorbed, the deposition of new bone was found. The results indicate that magnesium is biocompatible, osteo-conductive and is a potential material for use as a degradable bone implant.
  • WANG Xiaoping, WANG Leyun, DU Xuan, CUI Fuzhai, MA Xiao, HUANG Yifei
    By two step acid-alkali pretreatment and immersing into supersaturated calcification solution, hydroxyapatite (HA) coating was deposited on titanium (Ti) discs. The composition, surface morphology and cross-section of the coating were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Fibroblasts of rabbit cornea were seeded on HA coated Ti disc, pure Ti disc and glass. Cell adhesion, proliferation and morphology were detected at 24, 48 and 72 h, respectively. It is shown for the first time that HA coating can significantly enhance the adhesion and proliferation of rabbit corneal fibroblast in comparison with that of pure Ti.
  • FANG Zhengping, WANG Jianguo, GU Aijuan, TONG Lifang
    The effect of multi-walled carbon nanotubes (MWNTs), both amino-functionalized (f-MWNTs) and unfunctionalized (p-MWNTs) on the curing behavior of epoxy resin (EP) cured with triethanolamine (TEA), was investigated using differential scanning calorimetry (DSC). Because the triethylenetetramine (TETA) grafted on the f-MWNTs could act as curing agent and the produced tertiary amine as negative ionic catalysts of curing reaction of EP, so the activation energy of the EP/TEA system was decreased by the addition of f-MWNTs. Viscosity played a key role in the curing behavior of the EP/TEA/MWNTs system, for high viscosity of the EP/TEA/MWNTs system could hinder the motion of the functional groups. The curing heat in EP/TEA/f-MWNTs (weight ratio 1/0.1/0.01) system was higher than the neat EP/TEA (weight ratio 1/0.1) system, while the curing heat in EP/TEA/p-MWNTs (weight ratio 1/0.1/0.01) was lower than the neat system. When the content of f-MWNTs was increased to 2 phr (weight ratio of 1/0.1/0.02), the curing heat became lower than that of the neat EP/TEA system, which was the result of the higher viscosity of the EP/f-MWNTs/TEA system. Since the curing heat indicated the curing degree of the system generally, the addition of the f-MWNTs was thought to increase the curing degree of the epoxy matrix at a relatively low content.
  • WANG Xuelin, WANG Keming, CHEN Feng, LU Qingming, MA Hongji, NIE Rui
    The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 2.8 MeV O+ ion implantation with the doses of 8×1014 and 2×1015 ions/cm2 at room temperature. The waveguides were characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 300°C for 20 and 40 min in air. The refractive index profile is reconstructed using the reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and a slight change increases with the doses, which are different from most of the observed ion-implanted waveguides.
  • LIN Zhihui, WU Wenhui, WANG Jianquan, JIN Xin
    A series of hydrogels was synthesized from hydrophobic allyl phenyl sulfone (APS) and hydrophilic 2-hydroxyethyl methacrylate (HEMA) by bulk free radical copolymerization. The effects of APS content and temperature were studied on network parameters such as effective crosslink density (ve), molar mass between crosslinks (Mc) and polymer-water interaction parameter (χ) of hydrogels. The increase in APS content was shown to enhance hydrophobic bonding within hydrogel, leading to the decrease in equilibrium water content (EWC) and the increase in volume fraction of polymer in hydrogel (φ2), tensile strength and Young s modulus. At the same time, the increases in ve and χ and the decrease in Mc were also observed. When the temperature is increased from 273 to 343 K, the hydrogel A/H3 undergoes decreasing in EWC and increasing in φ2 and χ values. The thermodynamic analysis indicated that the swelling process is an exothermic process.
  • MA Guiping, YANG Dongzhi, ZHOU Yingshan, JIN Yu, NIE Jun
    Ultrafine fibers of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) (CS/PVA/PVP) were prepared via electrospinning. The structure and morphology of CS/PVA/PVP ultrafine fibers was characterized by the Fourier transform infrared (FT-IR) spectroscope and scanning electron microscope (SEM). Furthermore, the effects of the concentration of PVA, PVP and the electrospinning voltage on the morphology of ultrafine fibers were investigated by the SEM. When the concentration of PVA was at the range of 30wt%–40wt%, ultrafine fibers could be obtained. The diameter distributions of ultrafine fibers decreased when the electrospinning voltage increased from 20 to 30 kV. The rough surface fibers could be obtained after etching with CHCl3.