Materials Science Forum Vols. 620-622

Abstract: The cement-fly ash stabilized crushed-stones are prepared with different cements, which SO3 contents are 1.8%,2.6%,3.4%,4.2%,5.0%,5.8% and 8.8%，and their 28d splitting strengths, 28d resilient modulus’s, expansion -shrinkage and dry shrink anti cracking coefficients are studied. On these bases, the influence of SO3 content of cement on shrinkage cracking resistance is analyzed. The mechanism of compensating shrinkage by micro expansion in pavement base and the function of SO3 on cement-fly ash binder are also explored in paper. It is proved that the increase of SO3 content in a suitable scope (1.8%-5.8%) can improve the drying shrinkage cracking resistance of cement-fly ash stabilized crushed-stones when the content of fly ash is 10%。But the structure and the performance of materials will be destroyed if the SO3 content of cement increases excessively (>8.8%).

Abstract: One fiber stain measure and control system has been designed to meet the problem that the magnitude and uniformity of the fiber strain directly determine the properties and longevity of the carbon fiber continuous sucker rod during the pultrusion process. In this system, there are 2 key technologies. The first one is the sensor that is used to measure the micro bend strain of the carbon fiber during the pultrusion process, designed base on fiber micro-bend principle, using silicon film as sensitive element and fabricated by silicon integrated circuit technology and three dimensional processes. Another is the executive unit of the system: Magneto-rheological Fluids torsional damper, which is designed base on one type of intelligent material named Magneto Rheological Fluids which can change its viscosity in millisecond according to the magnetic strength around it. So this paper provides a technical means to ensure the quality of the pultrusion process applied in fabricating the carbon fiber continuous sucker rod.

Abstract: The effects of the process parameters on the deformation behavior of Ti14 alloy have been investigated by compressive tests, at temperature between 1000°C and 1150°C and with strain rates from 5×10-3 S-1 to 5S-1. The results revealed that deformation temperature and strain rate have significant effect on the peak flow stress, the flow stress decreases. The response time required by deformation was affected by the strain rates and liquid fraction was done by the temperature. At higher temperature, transforms deformation mechanism was changed from sliding between solid particles to flow of liquid incorporating solid particles by the change of the liquid fraction.

Abstract: The microstructure, hardness and tensile properties of Mg-3Al, Mg-3Al-1.2Ca(AX31), Mg-3Al-1.2CaO(AO31), Mg-9Al, Mg-9Al-1.2Ca(AX91) and Mg-9Al-1.2CaO(AO91) alloys were investigated to identify the effect of CaO addition compared with Ca addition. The results show that the alloy element CaO has a good effect on high temperature tensile properties and CaO added alloys have superior high temperature performance compared with Ca added alloys. Addition of CaO results in the precipitation of Al2Ca phase (C15 phase) on the grain boundaries. This phase precipitated by the reduction of CaO leads to the refinement of a microstructure and improvement of tensile properties at elevated temperature similar to the Ca added Mg alloys. When added into molten Mg Ca makes solid solution in the Mg matrix up to 0.8wt %. But in case of CaO addition the thermally stable compound is precipitated directly without making solid solution with Mg matrix. Therefore, the high temperature tensile properties of CaO added Mg casting alloys are better than Ca added one at the same adding contents (1.2wt.%).

Abstract: Phase equilibrium of the Mg-Al-Sn alloy system was calculated in detail by utilizing phase diagram calculation commercial package and other thermodynamic data for Mg alloys. The calculated phase diagrams were compared with the DSC results for the alloys of Mg-3wt%Al-3wt%Sn. The solidification and precipitation process of Mg-3wt%Al-Xwt%Sn were analyzed. The detailed comparison strongly supports the reliability of the selected thermodynamic description based on the results of thermodynamic calculation. It is clarified that when the Mg-Al-Sn alloy ends its solidification and cools down continuously, the phase Mg2Sn precipitated first from solid solution of magnesium, and then the Mg17Al12 phase precipitated at relative lower temperature. This is shown that the calculation phase diagram method considerably reduces the effort of alloy design and that the reliability of the results is high.

Abstract: This paper investigated the use of electrostrictive polymers with compliant electrodes as a means of actuator. In many electrostrictive materials, especially polyurethane (PU) can produce large deformation and force because of its low elastic modulus.The electromechanical response is mainly due to Maxwell stress effect and electrostriction effect. When a thin film of dielectric elastomer is applied to an electric field, it will experience Maxwell stress caused by interactions of free charge between the electrodes and electrostriction caused by the reorientation of polar phase in the material. In this work, PU was composed of the soft segment with poly(dimethyl siloxane) (PDMS) and the hard segment with 4, 4’-diphenylmethane diisocyanate. Also the hard segment content of synthesized PU was controlled at 20, 25, 30, and 35wt%. To conclude, mechanical properties increased with the increase in hard segment contents. However actuation test showed that the deformation was decreased as hard segment contents increased.

Abstract: Silicon-based materials have been widely applied in industrial fields, such as microelectronic and solar power, for the specific electronic properties. In the present work, free-standing thick silicon coatings were fabricated by air plasma spraying (APS) and vacuum plasma spraying (VPS) technologies. The microstructure and electrical property of the coatings were characterized. It was found that the electrical resistance of APS-Si coating was higher than that of VPS-Si coating. The impedance spectroscopy results showed there was significant difference in impedance curves of APS-Si and VPS-Si coatings. The grain boundary semicircle appeared in the plot of VPS-Si coating, while did not appeared in that of APS-Si coating. It was thought that the electrical property difference of the two kind coatings was related with the oxidation and microstructure difference of the coatings.

Abstract: Failure of dental implant is often caused by specific pathogenic bacteria. In this paper, antibacterial HA coating was prepared by vacuum plasma spraying with silver loaded zirconium phosphate containing HA as feedstock. The antibacterial activity against Aa，Fn and Pg was evaluated using a film covering method. MTT colorimetric assay was used to measure cytotoxic effect of the antibacterial HA coatings. Results show that the HA coatings displayed significant antibacterial activity against Aa，Fn, Pg and no cytotoxicity to L929 murine cell lines when the content of silver-loaded zirconium phosphate antimicrobial is between 5wt% to 10wt%. The sensitivity of the bacteria to the antibacterial HA coating is in sequence of Pg >Fn >Aa.

Abstract: Fillers play important roles in the performances of silicone rubber, such as mechanical and physical properties. In this paper, the silicone rubber filled with silica in a wide volume range was measured in order to study the effects of filler loading on the mechanical properties of silicone rubber. The composites samples added with surface treated silica filler was characterized by Scanning Electron Microscopy (SEM) and fluorescent microscope with that reinforced by the unmodified filler as a comparison. The results showed that the surface treated filler are more easily diffused without agglomerate in the polymer network compared to the unmodifiedd filler. Incorporation of modified filler loading leads to the increase in both tensile strength and the elongation at break, but along with further increase in filler content, mechanical properties of silicone rubber decreased due to the filler particles aggregate state, which can be observed by SEM images. The tack-free time and the hardness of the silicone rubber decrease as the filler loading increases.

Abstract: New composite binder systems have been developed to improve strength of shell mold and to decrease processing time, as functions of dipping time and binder composition, which is compared with the conventional binder system. The new binder systems were prepared by mixing tetraethyl orthosilicate (TEOS) and polydimethyl siloxane (PDMS) as precursor of SiO2 and sodium methoxide (NaOMe) as precursor of NaO2. The samples of shell mold were dipped into the prepared binder systems, and then heat-treated at 1000°C for 1 hr. The fracture strength is sharply enhanced in the new binder system owing to the increase of penetration depth with the dipping time, whereas the conventional binder system is modestly increased even in the dipping time of 2 hr. The new binder system with 7.6 wt% PDMS shows the highest nominal strength, showing a nominal value of 16 GPa. When only PDMS as precursor of SiO2 was used in the new binder system, the increase of viscosity by PDMS causes a larger scattering in the strength value. The strength could be controlled with the dipping time and molecular weight, showing the lower nominal strength values at the dipping time of 0.5 hr and in the low molecular weight of TEOS/NaOMe. The relationship between strength and binder composition is discussed, based on the microstructures before and after heat-treatment.