Advanced Materials Research Vols. 299-300

Abstract: The minimum switching field threshold and switching speed are important parameters for the magnetic recording in writing. This paper presents the dynamic precession of the moments of the grains based on LL equation, and that the impact of the volume of the grain on the switching speed is investigated under the condition of microwave assisted switching of magnetic moment.

Abstract: The 6061Al matrix composites reinforced with SnO₂-coated aluminum borate whisker were fabricated using squeeze casting method. The composite were extruded successfully at 350°Cwith different die angles. The experiment results illustrate that the die angle have important influences on the extrusion process. The surface quality of extruded composites was improved and the extrusion load was reduced with die angle increasing from 30 to 60 degree. The <111> and <100> textures for aluminum matrix were formed in all extruded composites. The dispersion degree of the <111> texture, the alignment degree and the average length of whiskers increases with die angle increasing. There is a suitable die angle for the optimization of the extrusion process of the present composite.

Abstract: The maximum thickness of the pure titanium metal coating by micro arc oxidation increases when current density increases, but the color isn’t even when the current density is too big. Thickness of the coating increases when voltage increases,but the color isn’t even when the voltage is too big. The better technical parameters are Na₂SiO3 100g/L, voltage 350V, current density 100A/dm², oxidation time 150 s, the thickness of the coating is 12 μm, the color is light-grey and even. The diameter of the holes of the coating increase when voltage or current density increases. The coating mainly contains O, Si and Ti elements. The coating’s micro hardness is 1000 HV.

Abstract: A new flexible polymer-cement mortar was prepared by adjusting the ratio of cement, polymer emulsion and solution. The effects of cement and different kinds of polymer emulsion on the construction performance of composite materials such as workability, anti-aging, flexibility and impact resistance were evaluated. It was indicted that the prepared flexible polymer-cement mortar possessed a good application prospect.

Abstract: Microstructure of creeper treads is inhomogeneous when they are produced by way of common casting, which lead to lower mechanical properties. Compound loading and feeding are introduced into the technology of liquid forging. Defects of filling incompletely, shrinkage porosities and cavities are usually appeared in raised part of creeper treads. With feeding amount increased above 5mm, plastic deformation also would be increased, so the microstructure and mechanical properties of raised part were improved and those defects disappeared meanwhile. SiC_P/2A50 composite materials were used in order to enhance abrasive resistance and extend their service life. Creeper tread produced by compound loading and feeding could obtain homogeneous and fine microstructure. Average tensile strength and hardness of specimen reached 360MPa and HV115.97 respectively after (500°C×3h) solution treatment, (20min) quenching and (160°C×10h) artificial aging. The results show that inhomogeneous character of microstructure and mechanical properties of creeper treads could be overcome by compound loading and feeding.

Abstract: A large number of specimens with different contents of cement mixed superfine tailings, which took superfine iron tailings as aggregate, were produced to carry out a series of experiments on the mechanical properties of different ages and freeze-thaw cycling tests. The strength, load -deformation curve, frost resistance and other performances of cement mixed superfine tailings were obtained. The experiment data were compared with cement mortar and cement-mixed soil ones under the same conditions. The results are listed as follows: on even ground, the strength of cement-superfine tailings can be 4-6 times higher than that of cement-mixed soil, and about 10% lower than that of cement mortar; the relation of load-deformation and the characteristics of freeze-thaw cycles are basically the same as cement mortar under the same conditions.

Abstract: Composites have achieved much attention because of their excellent qualities. Core-shell γ-Fe₂O₃/Au nanoparticles were prepared by chemical reduction. Their optical properties and morphology were characterized by UV-visible spectrum (UV-vis), X-ray diffraction (XRD) and Transmission Electronic Microscopy (TEM). Furthermore, the average particle size and interface structure were also analyzed using small angle X-ray scattering (SAXS).

Abstract: Wearability of SiC_p reinforced aluminum matrix composites creeper treads was studied. Wear resistance of these creeper treads was tested by sliding friction pin-disk tester at room temperature. Friction morphology was observed and the friction mechanism of these creeper treads was investigated. The experiment parameters such as SiC_p particle size, volume fraction, mixing temperature, mixing time were adjusted and the best parameters were found through the tests. The results showed that the creeper tread had the most excellent wearability, high strength and hardness with 875r/min mixing speed, 40min~60min mixing time, 660°C~700°C mixing temperature, 7μm SiC_p particle size and the 10vol% SiC_p volume fraction. There were no microscopic holes and other defects in these dense composite materials. The interface between SiC_p and Al matrix was clean and straight, where Al₄C₃ brittle phase wasn't observed.

Abstract: The effects of complex modification which mainly consisted of mixed rare earth oxides and CaCO₃ on microstructure and properties in Mg₂Si reinforced hypereutectic A1-Si composite were researched. The results indicated that the morphology of Mg₂Si particle changed from irregular or crosses to polygonal shape, and its size obviously decreased. The hardness and wear resistance of the composite were improved by the complex modification.

Abstract: Al₂O₃ coated polyhedral Fe nanocapsules were prepared by arc-discharging a Fe-Al(8at%Al) alloy. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy, and network analyzer were employed to investigate the microstructures, compositions and electromagnetic properties (2-18GHz). The reflection loss R(dB) of the nanocapsules reaches to -50.5dB at 7.9GHz with a 3mm thickness, and EM absorption properties(RL<-20dB) in the 5.2~16.1GHz range with thickness range of 1.67-4.7mm. The excellent Microwave-absorption properties of as-prepared nanocapsules are ascribed to shape anisotropy and core/shell structure.