Papers by Author: Akihisa Inoue

Abstract: A new series of bulk metallic glasses were developed by addition of Fe into the ternary Zr60Cu30Al10 alloy. Although Fe-Cu element pair shows distinct immiscibility with a large positive heat of mixing, substitution of Fe for Cu significantly improves the glass-forming ability of the ternary Zr60Cu30Al10 alloy. The critical diameter for glass-formation increases from 8 mm for Zr60Cu30Al10 alloy to 20 mm for Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys. As compared with the ternary Zr60Cu30Al10 alloy, the new quaternary Zr-Cu-Fe-Al alloys show lower liquidus temperatures. The Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys, the best BMG-formers in this alloy system, are found to locate very near a Zr-Cu-Fe-Al eutectic point. The new Zr-Fe-Cu-Al bulk metallic glasses exhibit high strength of about 1700 MPa. The plastic strain increases from 7.8% to 11.3% with increasing the content of Fe from 0 to 12.5%. The finding of a Ni-free Zr-based bulk glassy alloy with the extremely high glass-forming ability is expected to extend the future application of bulk metallic glasses.

Abstract: Molecular dynamics (MD) simulations based on a plastic crystal model (PCM) were performed for a Pd0.4Ni0.4P0.2 alloy in Metal-Metalloid (M-MLD) type of bulk metallic glass (BMG). Two kinds of clusters of cubeoctahedron capped with four half-octahedra and trigonal prism were used as initial atomic arrangements of the Pd0.4Ni0.4P0.2 alloy. Random rotations of clusters around their centers of gravity and subsequent structural relaxation vitrified the alloy. The high glass-forming ability of the Pd0.4Ni0.4P0.2 alloy is due to the critically-percolated, cluster-packed structure that is a universal feature for both M-MLD and M-M types of BMGs.

Abstract: . It is known that bulk metallic samples reflect microwaves (MWs) while metallic powdered samples can absorb such radiation and be heated efficiently. The present paper shows a direct evidence of penetration of MW radiation into and through a layer of metallic powder and contains theoretical explanation of such behavior.

Abstract: Recently, Ti-based metallic glasses aim at biomaterials with their high specific strength and superior corrosion resistance. Their high workability also shows a good performance for mass production under the energy saving environment. In this study, we started investigation of the design of Ti-based metallic glasses with the restricted alloying elements for biocompatibility and characteristic evaluation of the optimized Ti-based metallic glasses with higher glass forming ability for dental implants. These Ti-based metallic glasses do not contain Al, V and Ni elements which are well known to be neurotoxicity and cytotoxicity for human body. Current medical reports of impracticability by these elements have been a hot issue in biomaterials science. Newly designed Ti-based metallic glasses exhibit good performances. Especially, the optimized Ti-based metallic glass has high corrosion resistance with better passivity in a wide passivation range in simulated body fluids at 310K. In addition, biocompatibility of Ti-based metallic glass was also evaluated by cell culture in vitro. Excellent biocompatibility of Ti-based metallic glass show high potentials to be applied as biomaterials that necrosis of osteoblast (SaOS2) was not detected in this study.

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: Apatite forming and bonding ability of Ti based bulk metallic glass ((Ti0.40Zr0.10Cu0.36Pd0.14)99Ca1: BMG) were investigated as a new type of biomaterials. Powder mixture of CaHPO4･2H2O and Ca(OH)2 and the BMG disks were treated with autoclave for hydrothermal hot-pressing simultaneously (150°C, 40MPa). And then the BMG disks were soaked in simulated body fluid (SBF, Kokubo solution). Apatite were deposited and covered on the surface of the BMG. It was firstly demonstrated that surface of Ti based bulk metallic glass could be revealed apatite forming ability.

Abstract: In this study, microwave (MW) heating of Fe powder in the separated electric (E-) and magnetic (H-) fields was performed first, and the heating behaviors on the field dependence were investigated. It was shown that they are heated better in H- field than in E- field. The MW heating mechanism of metals were briefly discussed. MW heating of soda-lime glass alone was not easy, however addition of iron powder enhanced the heating, depending on the volume fraction of the powder. Occurrence of deformation and melting of the glass spheres was observed. This technique is applicable to fabrication of glass-metal composites and vitrification of waste matters. MW heating of Ni-based metal glass was attempted with no external pressure and in an inert atmosphere, it was also shown that heating was better accomplished in H- field. Weakly sintered body was possibly obtained with retention of the amorphous phase.

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.