Papers by Author: Akihisa Inoue

Abstract: We investigated the effects of addition elements (Sn, Al, Si, Ag, Fe, Cr) with a small amount on the glass-forming ability, thermal stability and mechanical properties of the Ti-Zr-Cu-Pd glassy alloy system. The results revealed that minor Sn addition improved the glass-forming ability, thermal stability and plasticity, Si addition enlarged the supercooled liquid region, and Fe addition improved the plasticity, while minor additions of Si, Ag, Fe, and Cr lowered the glass-forming ability, and Al and Cr additions were harmful to the plasticity of the Ti-Zr-Cu-Pd glassy alloy system.

Abstract: We Successfully Prepared the Rod Glassy Samples of (Fe_1-xCo_x)₇₆Si₉B₁₀P₅ (x = 0~0.4) Bulk Metallic Glass (BMG) with the Diameters up to 3.0 mm by Substituting Fe for a Small Amount of Co Element. A Certain Amount of Co Substitution for Fe Contributes to the Increase of the Glass-Forming Ability (GFA) while Maintaining Good Mechanical Properties (the Fracture Strength up to 3700 MPa). This Co-Added Ferromagnetic Bulk Glassy Alloy System Also Exhibits a Higher Saturation Magnetization of 1.49 T and Lower Coercive Force (H_c, 1.2 A/m). The Fe-Based BMGs with Alloying a Small Amount of Co Element Demonstrate Excellent Combination of High GFA, Good Soft-Magnetic Properties as Well as High Strength.

Abstract: The crystal structure of the phase precipitated in a Zr-Cu-Al ternary alloy during quenching was investigated. The crystal structure is constructed by stacking several atomic layers periodically and is similar to that of the Laves phases. The reason why a Zr-Cu-Al alloy tends to crystallize into Laves-like periodic stacking order structure is discussed.

Abstract: Molecular dynamics (MD) simulations were performed for a Zr₂Ni alloy by referring to crystallographic features of a metastable Zr₂Ni phase. Simulation method was identical to our previous studies named plastic crystal model (PCM), which includes crystallographic operations for an intermetallic compound in terms of the random rotations of hypothetical clusters around their center of gravity and subsequent annealing at a low temperature. On the basis of MD-PCM, the present study considers an additional refinement named united atom scheme (UAS) on the motions of atoms in the hypothetical clusters. In MD-PCM-UAS, Dreiding potential was assigned for atomic bonds in a cluster whereas Generalized Embedded Atom Method potential for the other atomic pairs. The simulation results by MD-PCM-UAS yield a liquid-like structure. However, annealing did not cause subsequent structural relaxation, which differs from the results by MD-PCM and conventional MD simulations. Further simulations based on MD-PCM-UAS were performed for a nanostructure comprising clusters and glue atoms, leading to the best fit with the experimental data.

Abstract: Ti-based bulk metallic glasses with minor addition of Ag, Au or Pt elements were prepared by copper mold casting. The Microstructure of the as-cast samples was examined by TEM. Nanoparticles identified as cubic Pd3Ti with crystal planes of (111), (200), (220) and (311) are observed in all the alloys modified by the minor addition of Ag, Au or Pt. The results revealed that the glassy/nanoparticle composited alloys exhibited high strength about 2000 MPa and plastic strain between 1.5-10% due to the inhibition of propagation of shear band.

Abstract: With the aid of the atomic-cluster-plus-glue-atom model (ACPGA model) proposed by Dong et al [1] for bulk metallic glasses (BMGs), the formation and characteristic of Ni-Ta binary BMGs were investigated in this work. Binary glass-forming compositions containing 56.3–62.5 at.%-Ni were obtained by a composition formula [M-Ni₆Ta₆]Ni₃ based on the ACPGA model. It was found that Ni-Ta BMGs with a diameter of 2 mm was obtained over a composition range of 59 ~ 62 at.%-Ni by copper mold casting method, which are in good agreement with our model prediction. Newly-developed Ni–Ta BMGs are a kind of extreme materials, which exhibit superior thermal stability (T_g = 993K) and a ultrahigh fracture strength of about 3.5 GPa.

Abstract: Large-size Ni-based bulk metallic glass (BMG) composite samples exhibiting simultaneously high strength, enhanced plasticity and improved conductivity were produced by spark plasma sintering of mixed glassy powder blended with high-conductive Cu particulates. This opens new possibilities for the applications of the BMG composites as functional and structural materials.

Abstract: The inductor for a power supply is expected to have higher efficiency and capability of dealing satisfactorily with large current. Additionally, high corrosion resistance characteristics are also required for commercial inductors in practical use of. Thereby, we focused on Fe-based glassy metal alloys with both high magnetization and low magnetic anisotropy ［1］, and developed the novel glassy metal alloys with a chemical composition Fe97-x-yPxByNb2Cr1. In this glassy metal alloy, 1 at % Cr is the optimum composition for the realization of higher corrosion resistance as well as a high magnetic flux density. The glassy Fe97-x-yPxByNb2Cr1 (x=5-13, y=7-15) alloy exhibits the high glass-forming ability leading to the large thickness of 110-150 μm and low coercive force of 2.5-3.1 A/m due to higher structural homogeneity in wide range of composition. The large critical thickness of this alloy should be caused by the high glass-forming ability (GFA) due to the existence of the super cooled liquid region (Tx) of roughly 30 K. Therefore a Fe77P7B13Nb2Cr1 powder/resin composite core displays a much lower core loss of 650 W/m3 than the conventional amorphous Fe75Si10B12Cr3 powder/resin composite core by approximately 1/3.

Abstract: We investigated consolidation behavior of gas-atomized Cu50Zr45Al5 metallic glassy alloy powders by a spark plasma sintering (SPS) process. Density of the sintered samples increased with an increase in sintering temperature. The nearly full density samples without crystallization could be attained by the SPS process at sintering temperature of 693 K under pressure of 600 MPa. The produced samples exhibited high-strength and met large-size requirement. The SPS process makes it possible to fabricate the large-size bulk metallic glasses without limitation of dimensions and alloy system.

Abstract: Viscous flow behaviour of supercooled liquids and mechanical properties in Zr55+XCu30-XNi5Al10 (X=0, 5 and 10 at. %) and Zr65Cu18Ni7Al10 bulk metallic glasses (BMGs) have been examined. Viscosity has been measured by using a penetration viscometer at a high-speed heating rate of 400 K/min. With increasing Zr-content, Tg tended to decrease and Tx tended to increase, resulting Tx (=Tx-Tg) increaseing up to about 170 K under a heating rate of 400 K/min by the DSC analysis. The viscosity lowered about one order of magnitude, e.g., minimum value of the viscosity decreased from 3~4x106 Pa-s for the Zr55Cu30Ni5Al10 and Zr60Cu25Ni5Al10 BMGs down to 5~6x105 Pa-s for the Zr65Cu20Ni5Al10 and Zr65Cu18Ni7Al10 BMGs under the same heating condition. Compression tests were also carried out at a slow strain rate of about 1 x 10-4 s-1 at room temperature. With increasing Zr-content, the apparent yield stress was decreased but the total strain at fracture was increased significantly, suggesting that there is a strong relationship between viscosity and the mechanical properties in these BMGs.