Materials Science Forum Vols. 561-565

Abstract: Fe-based bulk metallic glasses with good soft magnetic softness, high strength and relatively low material cost should have greatest potential for wide variety of applications among many kinds of bulk metallic glasses (BMGs). However, the glass-forming metal elements such as Al, Ga, Nb, Mo and so forth in the Fe-based BMGs significantly decrease saturation magnetization (Js) which is a essential property as soft magnetic materials. Since the coexistence of high Js and high glass-forming ability (GFA) has been earnestly desired from academia to industry, however, has been left unrealized over many years. Here, we present a Fe76Si9B10P5 bulk glassy alloy exhibiting with unusual combination of high Js of 1.51 T comparable to the Fe-Si-B amorphous alloy ribbons with thickness of about 25 μm in now practical use, because of not-containing the glass-forming metal elements, and high GFA leading to a rod with a diameter of 2.5 mm. This alloy composed of familiar and low-priced elements also has extremely low coercivity which should enable ultra-high efficient transformers, therefore, has a great advantage for engineering and industry, and thus significantly improves energy saving, conservation of earth resources and environment.

Abstract: We prepared the Ni80-xCrxP16B4 (x = 3, 6, 9, 12, 15, 18, 21, 24, 27 and 30 at.%) alloy ingots in an Ar flow atmosphere without evacuation and then produced the alloy ribbons by melt-spinning in evacuation and air. Their thermal stability and other charasteristics were studied and the alloy composition was optimized. A supercooled liquid state appeared at Cr content of more than 9 at.%, and their Tg and Tx increased with increasing Cr content. The 2 Tx increases up to about 45 K with increasing Cr content up to 15 at.%, and then saturates in more higher Cr content. Thus we select the Ni65Cr15P16B4 alloy as an optimized composition for PEFC separator. Moreover, the precise grooves were successfully formed under viscous flow process. The groove-formed sample possessed a single glassy phase, and the Tg, Tx and 2Tx were not changed.It indicates that the sample was not thermally affected by hot-pressing in this experimental condition.

Abstract: Although a Ti47.4Zr5.3Ni5.3Cu42 glassy alloy does not occur precipitation of crystalline in annealing of prolonged time below glass transition temperature, it shows slightly embrittlement during passing through devitrification process. The embrittlment behavior may be connected to structural relaxation. Using ultrasonic, in this study, acoustic characteristics of the glassy alloy during progressive devitrification were examined in terms of structural relaxation. The structural changes are characterized by decreases in specific volume, bulk modulus, Lamè parameter and Poisson ratio, accompanied by structural relaxation.

Abstract: A 2mm-thick bulk amorphous Ni-W alloy is formed by applying a new electroforming process and its states are investigated by the XRD analyses and the EDS measurement. The homogeneities of the electroformed alloys are evaluated by the linear analyses on the cross sections of the sample. The fluctuation of the millimeter-scale W-concentration of the bulk amorphous alloy obtained in the present work is reduced to almost the same as that of the bulk nanocrystalline alloy reported in the previous work. Compared to the thin-film specimen produced by the conventional electroplating processes, the gradient of W-concentration of the bulk amorphous specimen can be reduced to two-fifth in the micrometer-scale profiles. Therefore new electroforming process can be successfully applied to the fabrication of the bulk amorphous Ni-W alloy.

Abstract: Nanocrystalline iron oxide powders were prepared by an inert gas condensation technique under various oxygen partial pressures. The as-prepared nanocrystalline iron oxide powders were further modified by electroless nickel plating. The as-prepared and modified nanocrystalline powders were characterized by X-ray diffraction, transmission electron microscopy, and synchrotron X-ray absorption techniques. In addition, magnetic properties of the iron oxide nanoparticles before and after electroless nickel plating were evaluated by vibrating sample magnetometer. The experimental results show that the as-prepared nanocrystalline iron oxide powders exhibited a mixture of iron and γ-Fe2O3 phases. TEM observations revealed that oxidation started from the surface of the gas-condensed iron nanoparticles. The amount of iron oxide increased with increasing oxygen partial pressure and was confirmed by synchrotron x-ray absorption examination. A decrease in saturated magnetization and coercivity of the nanocrystalline iron oxide powders was observed after electroless nickel plating.

Abstract: A simple method was reported for synthesis of carbon nanofibers. Ethanol burner was employed as the setup. Different morphological carbon nanofibers were synthesized by the decomposition of ethanol. As-grown carbon nanofibers were characterized. The results indicate that depending on the size of catalyst, carbon deposits with different morphologies were produced.

Abstract: Carbon nanofibers have been obtained by the interaction of ethanol with metal chloride over copper plate. Different metal chloride was used as the catalyst precursor. The products were characterized by the Raman spectroscopy for the degree of graphitization. The relative intensities and the amount of amorphous carbon were estimated. The results indicate that the catalyst precursor has effects on the degree of graphitization of carbon nanofibers.

Abstract: The structure, thermal stability and elasticity of Zr50Cu40Al10 bulk metallic glass (BMG) have been investigated with reference to Zr70Cu30 and Zr70Cu20Al10 amorphous alloys. The thermal stability of Zr50Cu40Al10 is significantly enhanced in comparison compared with those of the others. The large total coordination numbers more than 11 around all constituent elements are observed in Zr50Cu40Al10. A change of the bulk modulus in the crystallization is extremely small in Zr50Cu40Al10. The present experimental results indicate that atoms in the Zr50Cu40Al10 glass are closely packed and its microstructure is fairly uniform. This results in the much higher thermal stability of Zr50Cu40Al10.

Abstract: Owing to their exceptional stiffness, strength, thermal and electrical conductivity, carbon nanotubes have the potential for the development of nano composites materials for a wide variety of applications. In order to achieve the full potential of carbon nanotubes for structural, thermal and electrical multifunctional applications, both single wall carbon nanotubes (SWNTs), double wall nanotubes (DWNTs) and multi wall nanotubes (MWNTs) need to be developed into fully integrated carbon nanotube composites. Full integration of nanotubes requires their development beyond conventional composites so that the level of the non-nanotube material is designed to integrate fully with the amount of nanotubes and where the nanotubes are part of the matrix rather than a differing component, as in the case of conventional composites. In order to advance the development of multifunctional materials from nanotubes, this research is focused on the simultaneous control of structural properties, thermal and electrical conductivity of fully integrated carbon nanotube composites. These are hybrid material systems designed to surpass the limits of rule of mixtures engineering and composite design. The goals are to implement designs to fully mimic the properties of carbon nanotubes on larger scales for enhanced thermal and electrical management in addition to controlled strength and toughness. These new approaches involve, functionalization, dispersion, stabilization, alignment, polymerization and reaction bonding, in order to achieve full integration. Typical examples of polymeric and ceramic matrices, as well as other material systems are presented and discussed.

Abstract: Pinpoint nano-crystallization in Fe-based metallic glass was achieved by 2.0MV electron irradiation. Circular nano-crystalline structure regions with about 1μm in diameter were formed in the metallic glass and they were well dispersed in the amorphous matrix. In Fe77.5Nd4B18.5 alloy, micrometer order hard magnetic nano-composite region was formed in non-magnetic metallic glass matrix by electron irradiation. Electron irradiation induced crystallization is very effective for obtaining superior functional metallic materials with fine magnetic domains.