Advanced Materials Research Vols. 79-82

Abstract: SEM experimental system was employed to investigate the fracture behavior of particle reinforced metal matrix composites (91%wt tungsten alloys) by in-situ experiments. The fracture patterns of tungsten alloys under tensile loading were examined. Multi-particle unit cell models containing some important microstructure characteristics of tungsten alloys were established. By using fixed point iteration method, the displacement constraint conditions were applied on the multi-particle unit cell and the mechanical properties of tungsten alloys under tensile loadings were simulated. Comparison of the experimental results and the numerical predictions shows a good agreement between them, verifying the rationality of the FE models using the fixed point iteration method.

Abstract: A novel rotating-die system was proposed to moderate the elastic swelling for molten polypropylene (PP) and wood/polypropylene (WPP) composite. The results suggested that the neat PP and WPP melts followed the psuedoplastic non-Newtonian pattern. The rotation of the die could moderate the extrusion load and entrance pressure drop. The die rotation effect appeared to be very pronounced for the PP with high wood contents and high extrusion rates. The decreases in extrusion load and entrance pressure drop were related with reductions of melt viscosity due to shear heating effect. The results practically implied that use of the rotating die system could increase the productivity in the extrusion process. In terms of elastic swelling, in all cases, it was found that the swelling ratio of neat PP and WPP melt composite increased with increasing shear rate, but for any given shear rates, the addition of wood particles and the use of rotating die caused decreases in swell ratio of the melts, the wood content being more well-defined than the die rotating speed.

Abstract: With the assistance of diethylenetriamine(DETA), well-crystalline PbSe cuboidal structures with different concave faces in each plane have been successfully prepared through a hydrothermal process using Na2SeO3 as selenium source at 180 °C for 48 h. The products have been characterized by means of X-ray diffraction, field-emission scanning electron microscopy and luminescence spectroscopy. The field emission scanning electron microscopy showed that the edge lengths of these cuboidal crystals ranged from 1.5 to 2.5 µm, and the edges of a cube crystal extend outwards from its core with a tiny cubic center leaving step-like faces. The shape evolution of PbSe crystal from eight-dendritic structure to cuboidal structure was observed and the possible growth mechanism was proposed. Results revealed that the temperature played a crucial role in the final morphology of PbSe microstructures, and other factors such as the solvent composition and the molar ratio of metal/chalcogen were also discussed. The photoluminescence (PL) spectrum of as-prepared PbSe crystals shows the photoluminescence emission spectrum consists of a main intense peak at 435 nm and a shoulder at 420 nm. This synthesis method could be extended to the morphogenesis of other inorganic crystals with complex forms.

Abstract: Carbon fiber reinforced silicon carbonitride ceramic composite (C/SiCN) was prepared by rapid electro-thermal pyrolysis chemical vapor deposition using liquid hexamethyldisilazane as precursor. The density of C/SiCN is 1.75g/cm3 and with 15% porosity. Microstructure characteristics of C/SiCN were examined by transmission electron microscopy and scanning electron microscope equipped with energy dispersive spectrometer. The mechanical properties were characterized by three-point bending test. Microstructure observation displays a high degree of coalescence between SiCN matrix and fiber filaments, but there also exist plenty of micro-pores within fiber bundle. It is different from that of C/SiC composite made by chemical vapor infiltration. Mechanical test exhibits a mostly obvious nonlinear fracture behavior, which can be explained by typical toughening mechanism of long fiber-reinforced ceramic matrix composite.

Abstract: The influences of Fe2O3 doping on crystallization characteristics and microstructural morphology in the SiO2-Al2O3-MgO-K2O-ZrO2-F glass were investigated by using differential scanning calorimeter, X-ray diffraction and scanning electron microscopy techniques. The results indicate that the addtions of Fe2O3 shift the crystallization peaks to higher temperatures and the crystallization peaks increases in magnitude and the gap values between two crystallization peak temperatures boarden with the increment of Fe2O3 contents.The star-shaped crystals of cordietite by dendritic-manner growths are homogeneously precipitated in the rusidual glass. The mica phases, which are precipitated at interdendritic cordietite phases and formed the plate shapes at the elevated temperatures. The mica crystals grow at the expense of cordietite phases and finally form the composites of mica/cordietite uniformly distributed.

Abstract: The effects of different extent of cold rolling on the aging properties in Cu-Cr-Sn-Zn alloy are investigated by hardness and electrical conductivity analysis and microstructure TME (transmission electron microscopy) observation of the alloy. The results shows that dislocations provide nucleation site for precipitation during aging treatment, and result in the precipitation hardening effect from a finer size of precipitates. At 60% ratio of cold rolling and aged at 450°Cfor 1h, the hardness and electrical conductivity can reach 171.3HV and 71.5%IACS respectively.

Abstract: An attempt was made to prepare hollow silica microspheres by an oil-in-water emulsion which proposed to use waste polystyrene organic solution as oil phase. Effects of the kinds and amounts of surfactants and the concentration of waste polystyrene solution on the nanosized hollow silica microspheres were studied. The prepared hollow silica microspheres were characterized by TEM, XRD, TG-DTA and particle size distribution analyzer. The experimental results showed that the waste polystyrene organic solution was successfully treated as oil core and the cores could be removed at about 350°C. Meanwhile, the obtained hollow microspheres were amorphous with an average particle size of 40nm. The hollow silica microspheres could be obtained with the selected surfactant.

Abstract: Corrosion properties of magnesium alloys coupled with foreign metals impose much influence on the life of the parts. In this paper, the corrosion properties of AZ31 magnesium alloy coupled with nitrided 40Cr steel were investigated through immersion test in saline solution and weight loss test combining with optical microscope (OM) and scanning electronic microscope (SEM) analysis. The results indicate that the anticorrosion properties of the AZ31 magnesium alloy coupled with nitrided 40Cr steel are higher than those of the AZ31 magnesium alloy coupled with unnitrided 40Cr steel. The mechanism is attributed to the resultant nitrided layer which reduces the conductive properties.

Abstract: In this paper, using piezoelectric patches bounded or embedded in composite material structures as actuators and sensors, the system for exciting the structure and sensing its dynamic response can be established. Extracting damage information from the response and monitoring the perturbations of structural dynamics can be implemented using wavelet analysis. This will conduce to the capture of the accurate time of damage occurrence. The method developed in this paper can help to build the system of online damage detection and health monitoring of composite material structures when they cannot be directly observed or measured.

Abstract: The influences of ultrasonic vibration (USV) treatment on the refining effects of primary Si particles and acicular five-element compounds with rich RE in high silicon Al-Si alloy with complex modification of P and RE were studied. The primary Si particles in this alloy was about 20 μm in size under direct USV for 2 min in the semi-solid temperature range, compared to about 30 μm in the alloy without USV. The primary Si particles in the former distributed more homogeneously and in regular shape, but had lower volume fraction of primary Si than that of the alloy without USV for the solid solubility of Si in α-Al matrix increased with USV. The eutectic Si of this alloy was modified moderately with 0.6% RE and long acicular compounds with rich RE formed which decrease the mechanical properties of alloy for the effect of cutting the matrix. Short rod-like compounds with rich RE about 10~15 μm in length were obtained with the combined effects of USV and T6 heat treatment.