Papers by Author: Hisamichi Kimura

Abstract: The Fe-based bulk metallic glass (Fe43Cr16Mo16C15B10) sprayed coating with the thickness about 220%m was successfully deposited on an aluminum alloy (A5052) metal substrate using an HVOF (High Velocity Oxygen Fuel) spraying process. All sprayed coating has still kept the amorphous state after spraying. The Fe-based bulk metallic glass coating shows good adhesion to the aluminum alloy metal substrate, and has a high hardness with HMV 913~1120. It has been found that better properties can be obtained in the sprayed coating by using finer powder.

Abstract: Micro flash butt welding of super duplex stainless steel with Zr-based metallic glass insert was carried out using the temperature controlling system. Zr55Cu30Ni5Al10 of Zr-based metallic glass with thickness of 0.05mm and Zr metal with thickness of 0.1mm and 0.5 mm were used as the insert materials, in order to improve weldability. The specimens were mounted on the dies using a Gleeble thermal simulator, and then, flash butt welding was made. After welding, Zrbased metallic glass insert became much thinner than Zr metal insert. The super-cooled liquid in the interface protruded outside due to the superplastic deformation. The formation of the protrusion discharged the oxide films on the butting surfaces and contact surface; resulting in metallurgical bonding through the fresh surfaces. The Fe-Zr metallic compound for Zr-based metallic glass insert was hardly observed. The micro flash butt welding with metallic glass insert was successfully accomplished for super duplex stainless steel.

Abstract: We started investigation of new Ti-based bulk metallic glass (BMG) alloys with higher glass forming ability (GFA) for dental implants for medical market. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, cylindrical rod specimens of newly designed Ti-based BMG alloys with produced by copper mold casting exhibit compressive strength of above 1800 MPa. Ti-based BMG alloys also have high corrosion resistance that is passivated at the lower passive current densities of approximately 10-2Am-2 in 1 mass% lactic acid, 10-2~10-3Am-2 in PBS (-) at 310K which are lower than those of pure Titanium and Ti-6Al-4V alloy. These BMG alloys have high potentials to be applied as biomaterials in various forms, such as melt spun ribbons and cylindrical rods.

Abstract: Bulk metallic glass (BMG) exhibits remarkable properties such as high strength, good stiffness and good corrosion resistance. However, the wear resistance of amorphous metals is not excellent as expected their high strength. It is thought that large local shear bands easily change into cracks for debris formation. The effective obstruction of shear band formation might be applied to improve the wear resistance of BMG. In this study, we tried to suppress shear band deformation by fine crystalline phase dispersion formed by semi-conductor laser irradiation. The microstructures of irradiated Zr-based BMG specimens were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The fine dispersions of crystalline phases are observed in the amorphous matrix. The optimum condition for laser irradiation was discussed.

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: Microstructure and mechanical properties in friction stir processed (FSPed) Zr-based bulk metallic glass were investigated. The microstructure in the friction zone (FZ) exhibits an amorphous “band-like” structure with a small number of nanoscale crystalline particles. On the other hand, the microstructure in the FZ near the finish point of the process exhibits a large number of nanocrystalline particles in size of less than 20nm and amorphous phase. The difference of the microstructure in each FSP region is explained from the difference of the heat input by FSP. The hardness in each FSPed region shows higher value compared with that of other Zr-based balk metallic glasses with almost the same volume fraction of crystalline phase.

Abstract: In this work, we prepared the melt-spun (Ni0.6Nb0.4)70Zr30 amorphous alloy membrane and designed a catalytic reactor for methanol steam reforming combined with the amorphous membrane. Comparing the permeated gas with the evaporated gas, it was found that carbon dioxide (CO2) and carbon monoxide (CO) gases were removed from the permeated gas by using the amorphous membrane. Therefore, purified hydrogen gas was obtained in the reactor. We successfully produced pure hydrogen by using the amorphous membrane.

Abstract: Spark plasma sintering (SPS), as a developed rapid sintering technique, has a great potential for producing larger metallic glassy alloy specimens in a variety of shapes than those fabricated by casting methods, and can readily produce composites by dispersing crystalline particles in the glassy matrix. In this study, the Ni52.5Nb10Zr15Ti15Pt7.5 bulk metallic glassy matrix composites dispersed homogeneously with ceramics ZrO2 particulates were fabricated by the SPS process. The plastic ductility of the Ni52.5Nb10Zr15Ti15Pt7.5 glassy matrix composites was improved by adding ZrO2 particulates into the glassy alloy. The matrix of the fabricated composites maintained a glassy phase after the SPS process.

Abstract: Viscous flow behavior in supercooled liquid region of as-cast and pre-annealed Zr55Cu30Al10Ni5 bulk metallic glasses has been examined by using a penetration viscometer under high-speed heating rate of 20, 200 and 400 °C/min. Applied load for the cylindrical-shaped penetration indenter with a diameter of 1 mm was varied from 0.049 N to 0.294 N. Viscosity was quite independent of these applied loads. By pre-annealing the bulk metallic glasses at 400 °C, the density of the glasses increased, while the viscosity and the activation energy for viscous flow in their soopercooled liquid decreased with the pre-annealing treatments. Corresponding measurements of the differential thermal calorimetry (DSC) have been also done.

Abstract: Characterization of heat-treated CaTiO3 thin films of 10, 20, 30 and 50 nm in thickness and their change after immersion in a simulated body fluid were investigated by grazing incident angle X-ray diffractometry and Auger electron spectroscopy (AES). The CaTiO3 films were prepared on titanium substrate by sputter-deposition of CaTiO3 target followed by heating in an electric furnace at 873 K in air for 7.2 ks. The CaTiO3 films were immersed in 0.8% NaCl solution for 14 d. All the films before heat treatment were non-crystallized films and after heat treatment, only the 50-nm film was crystallized to perovskite-type CaTiO3. In AES in-depth profiles after heating, Ca diffusion was not observed in the 50-nm film, whereas Ca diffusion toward the Ti substrate was observed in the 10-, 20- and 30-nm films. After immersion for 14 d, the vicinity of surface of the 10, 20 and 30 nm thick CaTiO3 films were dissolved into the NaCl solution, while the 50-nm thick CaTiO3 film was scarcely dissolved. Since dissolution from biomaterials in a human body has possibility to harm, the CaTiO3 film should be deposited more than 50 nm in thickness and heat-treated at 873 K.