Applied Mechanics and Materials Vols. 184-185

Abstract: Workability, an important parameter in magnesium alloys forming process, can be evaluated by means of processing maps on the basis of dynamic materials model, constructed from experimentally generated flow stress variation with respect to strain, strain rate and temperature. To obtain the processing maps of extruded Mg-Zn-Mn-Y magnesium alloy with different secondary phases (I-phase and W-phase), hot compression tests were performed over a range of temperatures 523–673 K and strain rates 0.001~10s-1. The response of strain-rate sensitivity (m-value), power dissipation efficiency (ζ-value) and instability parameter (n-value) to temperature and strain rate were evaluated. By the superimposition of the power dissipation and the instability maps, the dynamic recrystallization (DRX) and instability zones were identified and validated through micrographs. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro-structural modification.

Abstract: Poly(viny1 alcohol) (PVA)/regenerated silk fibroin (RSF)/silicon dioxide (SiO₂) fiber mats were prepared by electrospinning of composite solutions. Fiber morphology was observed under a scanning electron microscope and effects addition of SiO₂ was evaluated. Results showed that the obtained fibers exhibited a smooth outer surface, and the continuity was improved because of the different solution conductivity, solution viscosity and compatibility of PVA and RSF by the addition of 1.0 wt. % SiO₂. It was found that both Si-O-C linkage and hydrogen bonding interactions were existed among SiO₂, PVA, and RSF by FTIR spectroscopy. The addition of SiO₂ also resulted in the decrease of crystallinity and increase of thermal properties of electrospun fibers, which were suggested as a result of enhanced compatibility and physical properties of PVA and RSF composite.

Abstract: In this paper, the in vitro blood compatibility of micro-arc oxidation (MAO) alumina coatings prepared in different times on biomedical NiTi alloy was studied using hemolysis ratio, dynamic blood clotting and platelet adhesion. The results show that the blood compatibility of the coated NiTi alloy is much better than that of uncoated NiTi alloy and reduces with increasing the micro-arc oxidation treatment times. Therefore, it can be concluded that the blood compatibility of materials is mainly dominated by the surface species contacted with blood within some ranges of surface roughness, not the surface morphologies, and the MAO alumina coatings can effectively improve the blood compatibility of NiTi alloy

Abstract: Hydrogel beads with different diameters were prepared by double coacervation method of alginate with CaCl2 followed by complexation between alginate and chitosan. The main purpose of this study was to evaluate the morphological properties of beads under different conditions and prepared by different drying methods, which would have a major effect on the other characters and applications of beads. The results show that the beads can be manufactured with the control of concentrations of the two polymers and diameter of the syringe needle. Different drying methods can affect the morphological properties of the beads.

Abstract: The tensile properties and fatigue properties were tested, and the fatigue fracture and damage behaviore of Al-5Zn-2Mg high strength aluminum alloy was investigated by means of optical microscope (OM) and scanning electron microscope (SEM). The results show that the grain of the Al-5Zn-2Mg high strength aluminum alloy is elongated after rolling deformation. The tensile strength of the Al-5Zn-2Mg aluminum alloy is 470MPa. The fatigue life is 6.4×104 cycle in R=0.1, f=99Hz, and σmax=210MPa. The average rate is 0.08μm per cycle from micro crack formed to 8mm of fatigue crack length. The fatigue crack forms in the surface. There are the fatigue striations in the fatigue crack propagation area. The crack velocity is about 2μm per cycle in propagation area. The damaged microstructure with the fatigue loading is loose, that indicates the micro cracks progressively emerge.

Abstract: The SnO2 powders have been prepared by hydrothermal method at temperatures of 150, 180 °C from SnCl2•2H2O, NaOH and sulfur (S) powder. The phases and morphology of the products were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. Experimental results show that, no impurity phases were found except SnO2 and no regular geometric shapes were observed in this product powders. The reaction mechanism is that SnO2 may be obtained by decomposition of Na2SnO2 formed from Sn(OH)2+NaOH.

Abstract: The influence of precipitated phases in Ni-based alloys during solid solution aging treatment on the performance of Ni-based alloys was investigated by means of metallographic observation, scanning electron microscope (SEM), and transmission electron microscope (TEM). The variation of microstructure and resultant phases as a result of solid solution aging treatment at different temperatures was discussed. The results show that the heat treatment temperature has significant influences on the type as well as quantity of precipitation phases. Lots of phases precipitated at grain boundaries, the distribution of precipitated phases are characterized by mesh-like structure. The corrosion tests results indicate that there is a potential difference between grains and grain boundaries due to the precipitation of chrome carbide at grain boundaries, resulting in pitting corrosion occurred preferentially at grain boundaries, consequently, the corrosion resistance of Ni-based alloys is reduced. In order to enhance the corrosion resistance of Ni-based alloys, it is expected to control the carbon content in a lower range and proper heat treatment process to avoid large amount precipitation of chrome carbide.

Abstract: The low-cycle fatigue behaviors of permanent-mold cast and die-cast Al-Si-Cu-Mg-Sc alloys at room temperature were investigated. The results show that at the higher total strain amplitudes, both permanent-mould cast and die-cast Al-Si-Cu-Mg-Sc alloys exhibit the cyclic strain hardening. However, at the lowest total strain amplitude, the cyclic strain hardening occurs in the initial and middle stages of fatigue deformation and the stable cyclic stress response is noted in the later stage of fatigue deformation for the permanent-mould cast alloy, while the cyclic strain hardening phenomenon is observed during whole fatigue deformation for the die-cast alloy. At the same total strain amplitude, the die-cast alloy shows the higher cyclic deformation resistance than the permanent-mold cast alloy. Compared with the permanent-mold cast alloy, the die-cast alloy possesses the longer fatigue life at the lower total strain amplitudes. The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior for both permanent-mold cast and die-cast Al-Si-Cu-Mg-Sc alloys

Abstract: The cyano-bridged complexes [MA(en)x]y[Fe(CN)6]z·nH2O(MA=Co2+、Gu2+) have been synthesized. In the multi-metal compound [Co(en)3] [Fe(CN)6] ·6.1H2O was prepared. Infrared spectra with stretching vibration CN = 2117.27 cm-1 illustrates that there exists the bridged cyanide on the compound; the Curie temperature Ө is -8.23117 K, indicating the magnetic interaction between the metal ions in the compound is very weak.In the multi-metal compound CuII3[FeIII(CN)6]2·3NH3·6H2O, we shows firstly the coexistence of ferromagnetic order and spin-glass order.The irreversibility in the MFC/MZFC and the relaxation of MZFC suggest that the magnetic system can be visualized as containing a ferromagnetic cluster of spin below Tc, mixed with small spin-glass clusters formed below temperature Tg less than Tc. The observed magnetic properties are explained with a ferromagnetic-spin-glass phase model.

Abstract: Cold-drawn pearlitic steel wires are widely used in numerous engineering fields. One of the most powerful analysis methods on determining the dislocation character of this heavily cold worked material is to investigate the X–ray diffraction line-profile broadening. Fourier line–broadening analysis in steel wires with near eutectoid composition indicates that with cumulative true strains, the initial dislocation density of 6×10¹⁴m^-2 in the rods increases at least one magnitude in wires. Up to 1.5×10¹⁶m^-2 of dislocation density is found in the ferrite lamella of wires with a true strain of 2.77.