Advanced Materials Research Vols. 146-147

Abstract: Syntactic foams are widely used in many impact-absorbing applications and can be employed as sandwich core. To improve their mechanical performances, these composite sandwich structures have to be modelled. This approach requires the characterisation of the foam behaviour. Moreover, the microstructure of the syntactic foam has an influence on its macroscopic behaviour; the foam density, the diameter of the porosities, their distribution in the material have to be taken into account.

Abstract: A new method, covering slag technology combining rotating cylinder method, has been proposed in this paper for measuring the viscosity of the molten amorphous alloy, and the viscosity of molten Zr50Cu50 alloy was measured. Furthermore, the changes of viscous activation energy Ev were analyzed. The measurement results showed: the viscosity of molten Zr50Cu50 alloy increases with decreasing temperature in the range of 1373 to 1208K and there is an overall exponential relationship. Two discontinuous points on the curve of lnη ~1/T have been found. After analyzing the changes of viscous activation energy Ev , the microstructure of molten alloy could be changed. The viscosity of molten Zr50Cu50 alloy is three orders of magnitude higher than that of some other alloys which is closely related with the excellent GFA of Zr50Cu50 alloy.

Abstract: Stray current is one of the main reasons in pipeline failure. In pipeline design and maintenance, it is important to know the fundamentals influencing stray current corrosion. However, it is difficult to control stray currents because many factors can affect its inflow points, outflow points and current densities. Several fundamental aspects, such as soil resistivity, coating worn rate, buried depth and horizon distance have been studied in order to find useful information in pipeline design. The results show stray current can be influenced by soil resistivity, coating worn rate and buried depth. It is suitable to control stray current corrosion by increasing soil resistivity, buried depth, horizon distance and decreasing coating worn rate. However, there are boundary values in controlling stray current corrosion by increasing soil resistivity, buried depth and horizon distance. For example, in this laboratory study, the boundary horizon distance is 200mm.

Abstract: The Sr0.75La0.25Fe11.75-xCo0.25ZnxO19 hexaferrites are prepared by the ceramic process. Influences of the substitution of Zn2+ ions on crystallographic texture have systematically been investigated by pole figure analysis. The (008) and (107) pole figure shows that the pole intensities are axisymmetric at the center of c axis. With the increase of x, the lattice parameters a and c increase gradually till x=0.15. Excessive Zn2+ addition induces the much coarse grain. The easy-axis alignment of grains decreases from 77.5% to 75.5% for the substitution of Zn2+ ions from 0 to 0.25. When Zn2+ content was from 0 to 0.25, the magnetic properties of Br and (BH)max were increased, while Hcb and Hcj were decreased till x>0.2.

Abstract: The Al-20%Si alloy was prepared by mixing the high temperature melt of hypereutectic Al-30%Si alloy with the pre-crystallized low temperature hypoeutectic Al-10%Si alloy melt and then superheating the mixture, i.e., melts mixing and superheating (for short: MMS), combining with chemical metamorphism. The effect of pre-crystallized characteristic of the mixed melt on microstructure of Al-20%Si alloy was then investigated, The primary Si granules of the sample, poured by melt mixing with different composition and temperature, were well distributed with a grain size of less than 36μm. And after superheating, the primary Si phase of the mixed melt could be further refined and distributed more uniformly, which if adding the modificator into the mixed melt, the size of primary Si were been deceased and refined by less than 20μm. The analysis result shows that the decrease in the temperature of the mixed melt, from the average temperature of 740 °C for the mixture of Al-30%Si (900°C) and Al-10%Si (580°C) to 670°C for present alloy, leads to the increase in the degree of undercooling, and consequently to the refinement of primary Si. During the superheating, the growth, local melting, as well as the proliferation of primary Si occurred because of the unhomogeneous micro-distribution of the temperature and composition within the mixing melt, resulting in the further decrease in the grain size of primary Si. And adding the modificator could promote the effect of modification of primary Si of MMS process on the hypereutectic Al-Si alloy.

Abstract: Na0.5Bi4.5Ti4O15-based materials with A-site vacancy were synthesized using conventional solid state processing. The (Li,Ce) modification of Na0.5Bi4.5Ti4O15-based materials resulted in the obvious improvement of the piezoelectric activity and dielectric permittivity. The dielectric and piezoelectric properties of Na0.5Bi4.5Ti4O15-based ceramics exhibiting a very stable temperature behavior, together with its high TC ~641oC, excellent piezoelectric coefficient ~28pC/N and very low temperature coefficient of resonant frequency, making the (Li,Ce) modified Na0.5Bi4.5Ti4O15-based ceramics a promising candidate for high temperature applications.

Abstract: Lotus fiber is produced from lotus stalks with pool dipping，sodium hydroxide boil degum and hydrogen peroxide bleach methods. The spinning properties of specific gravity, linear density, relative strength, relative strength variation coefficient and break elongation were tested. The components and structure of the lotus fiber have been analyzed and indicated with chemical, infrared spectroscopy (IR), X-ray diffractometer (X-RD) and scanning electron microscope (SEM). The results show that the lotus fiber has similar components, properties and spinning performance with jute and belongs to natural cellulose fiber.

Abstract: In this study, we have used the FE method to investigate the effect of in-plane residual stress and strain-hardening exponent on the indenter load, indentation work and residual depth. Based on the reverse analysis, the 304 stainless steel’s residual stress and strain-hardening exponent can be measured fromone simple indentation test by using spherical indenter. The comparison between residual stress or strain-hardening predicted from reverse analysis and the input residual stress or strain-hardening used in numerical indentation experiments shows good agreement.

Abstract: Severe Plastic Deformation（SPD）methods are hot research techniques of preparation of bulk ultrafine-grained materials and strengthening the material properties currently .Among the various SPD methods, ECAPT that a new method of ECAP （Equal channel angular pressing） organic integrates with TE（Twist extrusion）was key introduced for the frist time ,and experimental study on ECAPT technology for deformation and densification of pure Al and Mo powder sintered materials were carried out and the results were compared with that of ECAP in this paper.The results show that there have more effective and more stronger severe plastic deformation during the process of ECAPT and it improves the ability of material’s plastic deformation and strengthens the material properties.In forming process of ECAPT after three passes,the grain size of powder sintering reduces the average 200%, and there has its nearly full density and comprehensive performance materials to improve overall performance significantly.It is confirmed that there have better comprehensive mechanical properties of strengthening materials and more stronger severe plastic deformation during the process of ECAPT contrast to the ECAP, too.

Abstract: The effect of electromagnetic stirring on the inner quality and solidification microstructure of the GH 3030 superalloy ingots was investigated by casting experiments. As we know from the experiments, the solidification microstructure of GH3030 is the single-phase of austenite. With the electromagnetic stirring (EMS) the grains of the GH3030 ingots become finer significantly and the average grain size decrease as the currents of EMS increase. The results also show that the macrostructure of the ingots was improved significantly. The length of the shrinkage cavity with EMS become smaller and the porosity disappeared while the ingots without EMS have much porosity. And yet the macrosegregation always exists whether with EMS or not, but the chromium in the ingots with EMS is better distributed, and consequently the macrosegregation of chromium is inhibited.