Advanced Materials Research Vols. 146-147

Abstract: The effect of Sr on the microstructures and mechanical properties of Al-20 wt% Si alloys were investigated. The results show that with increasing of the Sr content, the primary silicon firstly changes from polygonal block or large plate to small block, then to large polygonal block, and a large number of honeycomb-like on the primary silicon block. The eutectic silicon firstly changes into a fine start with a long needle-like fibrous or branched further to a short stubby dendrite or worm-like, continuously columnar dendrite α of quantity increase. In addition, with increasing the Sr content, the elongation of alloy increases, but there are ups and downs, the tensile strength changes little after the first sharp increases in hardness is parabola. When the Sr content is between 0.04 wt% and 0.06 wt%, the morphology and mechanical properties is the most ideal.

Abstract: The stability is one most important product performance index, which can directly determine the quality of the partially stabilized zirconia (PSZ), and the stability of PSZ is always fluctuating in the commercial process, so how to accurately, quickly and easily predict the stability of PSZ in the preparation process is very important. In the present paper, a new mathematical model to predict the stability of PSZ was proposed, based on statistical theory (SLT) and support vector machine (SVM) theory, which relates the stability of PSZ and the influence factors, such as the holding temperature, rising rate of temperature, holding time, decreasing rate of temperature and hardening temperature. Typical data collected from commercial process were collected for the training samples and test samples. Then testing and analyzing was done. The results showed that the max relative error was 1.80%, the least relative error was 0%, and the average relative error was 0.58%. It is accurate and reliable to predict the stability of PSZ by SVM model. Besides, multiple influence factors can be comprehensively considered in the SVM model, thus a new highly effective method for predicting the stability of PSZ is provided for commercial application.

Abstract: Iron doped TiO2 nanoparticles with different doping amounts were prepared using sol–gel method and characterized. These materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). Photocatalytic activities of the supported catalysts were examined for decolorization processes of methyl orange (MO) solution under UV irradiation. The results showed that doping of Fe3+ enhanced the photocatalytic activity of TiO2/HZSM-5, and the optimum Fe3+ doping of Fe/Ti mole ratio for TiO2/HZSM-5 was 0.07%. Doping of Fe3+ did not change the surface morphology of TiO2/HZSM-5. The Fe3+-doped TiO2/HZSM-5 possessed the anatase structures and Ti-O-Si bonds did not form between the HZSM-5 bulk and the supported TiO2.

Abstract: By means of HAAKE RS105L cone and plate rheometer the rheological behavior of heterocyclic aramid concentrated solution, including viscous flow activation energy, non-Newtonian index, structural viscosity index of the heterocyclic aramid solution were studied. The effect of concentration and temperature of the solution and molecular weight of the polymer on its non-Newtonian behavior was investigated. The results showed that heterocyclic aramid concentrated solution prepared via low temperature condensation was non-Newtonian fluid. With the decrease of temperature, increase of solution concentration and heterocyclic aramid molecular weight, the deviation of the solution from Newtonian behavior decreased. The molecular weight of the polymer and the concentration of the solution affected the non-Newtonian behavior more intensively.

Abstract: Using ludwigite as raw material, the phase transformation and mass loss rate of ludwigite in the process of oxidizing roasting are investigated by DTA, isothermal TG, scanning electron microscopy (SEM), X-ray diffraction (XRD) techniques. The results showed that magnetite is transformed into hematite, serpentine is decomposed into forsterite at lower temperature (T＜700°C). The weight of ludwigite has a small loss below 600°C. The decomposed of szaibelyite dehydrated and formed into suanite about 700°Cis the main reason of causing ludwigite mass losses. By comparing the curves of ludwigite at different temperature from 700 to 900°C, the process of oxidizing roasting can be divided into three phases: characterized by a period of fast weight loss, and then followed by a mass gain. Finally, weight of sample is no longer change with prolongation of time. The final weight loss is 6.062%, 6.658% and 7.442% respectively for test temperature. Suanite can not be decomposed to form B2O3 and volatilized when the temperature of oxidizing roasting is below 1142 °C. It is found by XRD that paigeite and magnoferrite are the most stable composition without deterioration on oxidizing roasting. The experiment results can provide theoretical references for agglomeration and blast furnace smelting of ludwigite.

Abstract: This paper aims to study the effects of rare earth Cerium addition on mobility, solidification shrinkage, casting microstructure and hot tearing tendency of Al-4.5Cu alloy. Results show that by adding appropriate rare earth Cerium into the Al-4.5Cu alloy, the viscosity of liquid metals can be reduced, the mobility of alloy can be increased, and the shrinkage during the solidification of liquid metal can be reduced. Further more, as the tendency of alloy dendrite is inhibited and the microstructure of the casting alloy is improved, the alloy can be purified, its thermal conductivity can be enhanced, and the hot tearing tendency of it can be decreased remarkably. It proves that when rare earth Ceriumaddition in Al-4.5Cu alloy is 4w%, the mobility of Al-4.5Cu alloy will be the maximum, and its volume shrinkage will be the least. Meanwhile, the grains of alloy are refined and round. The alloy also shows the lowest hot tearing tendency.

Abstract: Lead-free solder is meeting the requirement of environmental protection, but the property performance of existing lead-free solder is hardly comparable to those of lead solder. In this paper, 0.6% Bi was added into SnXCuNi solder alloy to produce lead-free solder at low cost and high performance. Microstructure, phase composition, melting point, wettability and characteristics of weld interface have been studied and analyzed. The results show that SnXCuNiBi solder alloy are mainly composed of βSn, SnX, Cu6Sn5 and SnBi. The addition of Bi reduces the melting point and improves the wettability of the solder. The main component of the joint interface of SnXCuNiBi/Cu system is Cu6Sn5, which has shown the capability to keep relatively high shear strength at the joint interface.

Abstract: For nanoscale devices and structures, interface phenomena often dominate their overall thermal behavior. The feature scale of material interfaces usually originate from nanometer length and present a hierarchical nature. Considering to the limitations of the continuum mechanics on the characterization of nano-scale, the multiscale model featuring the interface could be very important in materials design. The purpose of this review is to discuss the applications of multiscale modeling and simulation techniques to study the mechanical properties at materials interface. It is concluded that a multi-scale scheme is needed for this study due to the hierarchical characteristics of interface.

Abstract: The tensile performance of the woven membrane materials shows three characters: nonlinear, anisotropic and non-elastic. Besides, when suffering from the bi-axial loads, the tensile property of the woven membrane material is more complicated. These features make the analysis of the tensile performance of woven membrane materials more difficult. The analysis methods including the elastic matrix method, the mathematical function method, and the mechanical model method have been discussed in details.

Abstract: In this paper, a preparation method concerning ceramic moulds with zirconia coating used for the investment casting of TiAl alloys has been described. The processing technology of ceramic moulds was verified successfully using the ceramic moulds with zirconia coating prepared by recommended processing parameters. Interfacial reactions between ceramic moulds and TiAl alloys examined by OM (optical microscope), SEM (scanning electron microscopy) and XRD (X-ray diffraction) are presented in this paper. The results reveal that the thickness of interfacial reactions layer was about 20 μm.