Papers by Author: Yusuke Iguchi

Abstract: The purpose of the present study is to evaluate the processing property of Mg96Zn2Y2 of casting material. Mg96Zn2Y2 is a high strength magnesium alloy material newly developed by Mr. Kawamura in Japan. The name of this alloy is called as 'Kumadai Goukin'. For this purpose, cylinder upsetting tests were performed. In addition, the marketing community of AZ31 magnesium alloy collates the information with the new material. We examined and compared the deformation resistance and ductility of the two materials. Furthermore, the dependence of deformation resistance and ductility of these materials to processing temperature and speed was evaluated [1].

Abstract: Ultracentrifuge experiments were performed on the twinned Y1Ba2Cu3O7-x (Y123) single crystal at much lower temperatures than the melting point. Two layers structure with slightly different compositions was observed in the sample ultracentrifuged at 250°C(380,000 G), which might be due to the sedimentation of atoms. In the strong gravity layer, it was found that the Y123 phase disappeared, and unknown XRD peaks appeared. Decomposition occurred in the sample ultracentrifuged at 400°C.

Abstract: A visible four-layers structure with anomalous nano-sturucture was formed from a homogeneous -phase Bi3Pb7 intermetallic compound under a strong gravitational field (1.02x106 G, 130°C, 100 hours). In the 4th layer (lowest-gravity region), pure Bi particles precipitate. In the 2nd 3rd layers, composition graded structures, where Pb content increased along the gravity direction, were formed. It was found that the very broad XRD peak appeared in the 2nd layer, which indicated that an amorphous structure was contained.

Abstract: An atomic-scale graded structure has been formed by sedimentation of substitutional atoms under an ultra-strong gravitational field of 1 million G level in alloys and compounds. In this study, we investigate the sedimentation of impurity atoms in semiconductor materials under a strong gravitational field. High-temperature ultracentrifuge experiments (0.59×106 G, 400°C, 60 hours) have been performed on an InSb single crystal wafer which surface was coated with Ge by means of Physical Vapor Deposition (PVD). It was observed that the penetration depth of diffused Ge atoms under the gravitational field was several times larger than under terrestrial field at the same temperatures.

Abstract: The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 x 106 g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). 206Pb/208Pb and 207Pb/208Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy 208Pb isotope abundance increased and the light 206Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of 206Pb/208Pb versus 207Pb/208Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.

Abstract: In this study, we investigate the crystalline states and conditions for the grain-refinement of Bi70Sb30 (at.%) alloy. It was considered under an ultra strong gravity field, the crystals were fine-grained from the primary grain sizes of several mm to several tens of mm, and the crystal growth followed with formation of graded-composition structure due to sedimentation of atoms along the direction of gravity. It was found that for the crystal-grain refinement in Bi70Sb30 alloy the minimum gravitational field and the minimum time duration were at least 160,000 G and 10 hours, respectively at about 200 °C.