Materials Science Forum Vols. 539-543

Abstract: An attempt to prepare Fe2VAl deposited film and the thermoelectric module using RF sputtering has been made. Sputtering target has been prepared using mechanical alloying of metallic powders and the subsequent pulse current sintering process. The obtained deposited film has had a lack of aluminum content compared to the composition of the starting material. Controlling of aluminum content for the preparation of Fe2VAl sputtering target has made it possible to obtain the desired material composition. The film has had the experimental thermoelectric force being similar to the one estimated from the measured thermoelectric data of the materials. Fe2VAl thermoelectric module of eight pairs with a film thickness of 4 μm has had an electric force of 31mV and 5.6μW.

Abstract: Creatures have evolved extremely intelligent and complex adaptive systems for conducting their movements. They are protein motors with typical sizes of a few tens of nanometers. Protein motors include three major protein families, myosin, kinesin and dynein, which participate in a wide range of cellular processes, using energy from the hydrolysis of adenosinetriphosphate ATP. To harness these protein motors to power nanometer-scale devices, we have investigated effective and non-destructive methods for immobilizing protein motors on surfaces and to arrange the output of these motors, e.g. force and movement, to be in a defined direction. We found NEB-22 to be useful for retaining the abilities of protein motors to support the movement of protein filaments. We fabricated various patterns of tracks of NEB-22 on coverslips and protein motors were introduced and immobilized on glass surface. The trajectories of protein polymers were confined to these tracks. Simple patterns readily biased and guide polymer movement confining it to be unidirectional. In addition, having used dynein c purified from Chlamydomonas flagellar axoneme, we showed that microtubules driven by surface-bound dynein were self-organized into dynamic streams through collisions between the microtubules and their subsequent joining.

Abstract: Both bulk and thin film amorphous carbon were irradiated using a nitrogen ion beam and changes in surface roughness and composition after ion beam irradiation have been studied. Amorphous carbon thin films were prepared from toluene vapor using plasma enhanced chemical vapor deposition. Ion irradiation was performed at room temperature using a nitrogen ion beam and the ion beam energy was varied from 0.2 to 1.5 keV under the constant ion current density. Surface morphology was observed with atomic force microscopy (AFM). Depth profiles of nitrogen in the irradiated specimens were analyzed by X-ray photoelectron spectroscopy (XPS). AFM observations reveal that after the ion beam irradiation the surface of the bulk amorphous carbon becomes rough, while the surface of the amorphous carbon films becomes smooth. However, the notable difference in the surface roughness is hardly observed between low- and high-energy ion irradiation. From XPS studies, it is found that the nitrogen concentration near the surface increases after the ion irradiation for both bulk and thin films and irradiated nitrogen ions are combined with carbon, resulting in formation of carbon nitride layers. Depth profiles of nitrogen show that for the bulk specimen low-energy ion irradiation is more effective for the carbon nitride formation than high-energy ion irradiation, while for the thin films high-energy ions are implanted more deeply than low-energy ions.

Abstract: A new kind of nanocomposite rare-earth magnets of Nd2Fe14B/ α-Fe were prepared by melt-spinning method. Effects of alloying element and processing parameter on the microstructure and magnetic properties of nanocomposite materials have been investigated. Zr is effective to enhance coercivity of alloys because of a refinement of grains, so that in alloy of Zr content with 1.0 at% (Zr1.0) has the smallest grain size of 17 nm and therefore causes the highest intrinsic coercivity . Addition of Zr can also enhance the ability of amorphous-forming. The combination of adding of Zr and using a smaller diameter of the nozzle in the melt-spinning method is effective for the forming of amorphous structure. According to the MFM study, the length of the magnetic contrast in the alloy is much larger than the mean grain size. The large length corresponds to that of interaction domains(ID), which is related to the exchange coupling effect.

Abstract: Ba8Al16Si30 type I clathrate was produced by arc melting and thermoelectric properties were investigated. The phase transformation behavior of arc-melted type I Ba8Al16Si30 was examined by thermogravimetric analysis, differential scanning calorimetry, hardness test, density measurement, X-ray diffraction and scanning electron microscope analyses. Homogenization was carried out to induce the transformation to a thermoelectric phase at 773K to 973K for 5 hours and 24 hours in the vacuum furnace. Thermoelectric properties in the temperature range between 300K and 600K were measured and evaluated. Electrical conductivity was decreased and Seebeck coefficient was increased with increasing homogenization temperature and time. The arc-melted and the homogenized specimens represented n-type conduction at temperatures examined, and they showed reliable thermoelectric behaviors with increasing homogenization temperature and time.

Abstract: In this research, we investigated the fabrication conditions of Ti-Ni alloy powder by MA process and the shape memory characteristics of the sintered alloy by a pulse-current sintering equipment using mechanically alloyed powder (MA powder). The microstructure of the sintered alloy of the MA powder was more homogeneous than that of the alloy of the elemental powders. The application of the MA powder makes the width between transformation temperatures of the shape memory treated alloy of the MA powder became narrower, that is, it improves the temperature response of the compact. The tensile strength and elongation of the shape memory compact of the MA powder were approximately 780 MPa and 7.5 %, respectively. This is one of the superior tensile properties of SMA compact fabricated by powder metallurgy process. The superelastic behavior took place in the alloy of the MA powder. Thus, the MA process in short process time resulted in lower contamination of the MA powder and the application of the MA powder resulted in superior shape memory characteristics of the sintered alloy.

Abstract: The electromechanical properties of a newly proposed 3-dimensional piezoelectric transformer have been investigated. Especially, the effects of 3-dimensional geometry on the maximum tip displacement were carefully investigated. As a result, it was found that the maximum strain of the 3-dimensional piezoelectric device was significantly enhanced up to 4.5 times higher than that of a disk shape device. This data were in good agreement with the finite element model analysis of strains and vibration modes. Moreover, a very high voltage step-up ratio of 290 (10 times higher than the Rosen type), sustaining efficiency more than 96%, were achieved.

Abstract: CuAlNi shape memory alloy with Cu-13.5Al-4.5Ni(wt%) composition was prepared by cross-rolling method and the aging effect, phase transformation characteristics, microstructural variation were investigated. Transformation temperature was greatly increased in aged specimens at 250°C. Transformation temperature was not changed after the second reversed transformation, and Ms point was same in most specimens with third reversed transformation cycle. The variation of Ms point was not seen with aging at 100°C, but it was decreased with aging at 250°C. Transformation temperatures appear to be constant, to an measurable extent, in specimens prepared by both hotrolling and cross-rolling at 900°C. Plate shaped-specimen with the thickness of about 1mm was prepared by cross-rolling treatment at 350°C. The transformation temperatures did not change after the second transformation-reverse transformation cycling, and specially transformation start temperature was the same in most specimens experiencing third thermal cycle and thereafter. Undesirable tweed-like structure was observed in 250°C-aged specimen after a cross-rolling at 350°C. On aging the specimen prepared by cross-rolling, G.P zone was formed easier than that of γ2 phase. This phase was transformed to plate-like θ phase during aging.

Abstract: Stored energy plays a crucial role in recrystallization process. One can distinguish two contributions to this energy. The first one is the elastic energy, connected with residual stresses, i.e., with grain-grain interaction. Another part of the stored energy is due to dislocation density, which is mainly localized inside grains. The latter one is considered as a main driving force of recrystallization. However, the stored energy connected with residual stresses can also have some influence on this process. Both types of energy can be determined experimentally and predicted by deformation models. Taking into account both types of the stored energy, some features of recrystallization textures can be explained.

Abstract: Crystallographic texture has an important effect on the magnetic quality of electrical steel: a specific texture parameter A is defined and used to estimate the magnetic quality of texture components. It is shown that obtaining the best possible texture in non oriented electrical steel can reduce the losses with 1,5 W/kg. Two production schemes for high silicon electrical steel are described: a conventional processing through hot and cold rolling with adequate temperatures and cooling rates and an immersion-diffusion process by hot dipping in a Si- and Al-rich bath followed by diffusion annealing. The texture evolution in these experimental materials is under study and first results are reported for conventional alloys (rolling procedure) and for immersion-diffusion alloys, which are annealed after dipping in order to obtain a controlled concentration gradient with high Si and/or Al at the surface or a homogeneous Si and/or Al-content over the thickness.