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Author

Hisato Koshiba

Other affiliations: Alps Electric
Bio: Hisato Koshiba is an academic researcher from Tohoku University. The author has contributed to research in topics: Amorphous metal & Amorphous solid. The author has an hindex of 19, co-authored 56 publications receiving 1836 citations. Previous affiliations of Hisato Koshiba include Alps Electric.


Papers
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TL;DR: A Co43Fe20Ta5.5B31.5 glassy alloy exhibiting ultrahigh fracture strength, strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys.
Abstract: Bulk metallic glasses—formed by supercooling the liquid state of certain metallic alloys—have potentially superior mechanical properties to crystalline materials. Here, we report a Co43Fe20Ta5.5B31.5 glassy alloy exhibiting ultrahigh fracture strength of 5,185 MPa, high Young's modulus of 268 GPa, high specific strength of 6.0 × 105 Nm kg−1 and high specific Young's modulus of 31 × 106 Nm kg−1. The strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys1,2,3. Excellent formability is manifested by large tensile elongation of 1,400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultrahigh-strength alloy also exhibited soft magnetic properties with extremely high permeability of 550,000. This alloy is promising as a new ultrahigh-strength material with good deformability and soft magnetic properties.

512 citations

Journal ArticleDOI
TL;DR: The glassy alloy rods exhibit ultra-high fracture strength of 5185 MPa, high Young's modulus of 268 GPa and high specific strength of 6.5B31.

218 citations

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TL;DR: In this article, it was shown that an amorphous phase with a wide supercooled liquid region reaching 85 K before crystallization is formed in Fe−(Co, Ni)−(Zr, Nb, Ta) and Co−Fe−Zr−B systems.
Abstract: We have found that an amorphous phase with a wide supercooled liquid region reaching 85 K before crystallization is formed in Fe–(Co, Ni)–(Zr, Nb, Ta)–B, Fe–Co–(Zr, Nb)–(Mo, W)–B and Co–Fe–Zr–B systems. The high stability of the supercooled liquid enabled the production of bulk amorphous alloys with diameters up to 5 mm by copper mold casting. These amorphous Fe–(Co, Ni)–M–B alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.95 to 1.1 T, low coercivity of 1 to 8 A/m, Curie temperature of 560 to 590 K and low magnetostriction of 8–14×10−6. The effective permeability of the Co–based alloys exceeds 25 000 at 1 kHz and keeps high values above 5000 at the high frequency of 1 MHz. The permeability at 1 MHz is much higher than those for any kinds of soft magnetic materials. The frequency at which the imaginary part of permeability shows a maximum is also about 1 MHz. The success of synthesis of new Fe- and Co-based amorphous alloys with good soft magnetic properties and high glass-...

144 citations

Journal ArticleDOI
TL;DR: A new Co-based bulk glassy alloy Co 43 Fe 20 Ta 5.5 B 31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method.
Abstract: A new Co-based bulk glassy alloy Co 43 Fe 20 Ta 5.5 B 31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method. The glass transition temperature (T g ) is 910K and the supercooled liquid region (ΔT x ) reaches 70 K. The high thermal stability of the supercooled liquid enabled us to produce bulk glassy alloys with diameters up to 2 mm. These bulk glassy alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.5 T, very low coercivity of 0.9 A/m and very high permeability of 40000 at 1 kHz. It is noticed that the diameter of 2 mm is the largest value for Co-based bulk glassy alloys reported up to now. The success of forming the large-scale size Co-based bulk glassy alloy with high thermal stability of supercooled liquid and good soft magnetic properties is encouraging for future uses of bulk amorphous soft magnetic materials.

104 citations


Cited by
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Journal ArticleDOI
Akihisa Inoue1
TL;DR: In this article, the authors investigated the stabilization properties of the supercooled liquid for a number of alloys in the Mg-, lanthanide-, Zr-, Ti-, Fe-, Co-, Pd-Cu- and Ni-based systems.

5,173 citations

Journal ArticleDOI
TL;DR: The concept of high entropy introduces a new path of developing advanced materials with unique properties, which cannot be achieved by the conventional micro-alloying approach based on only one dominant element as mentioned in this paper.

4,394 citations

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the recent development of new alloy systems of bulk metallic glasses and the properties and processing technologies relevant to the industrial applications of these alloys are also discussed.
Abstract: Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

3,089 citations

Journal ArticleDOI
TL;DR: In this paper, the atomic size difference, heat of mixing (H mix), and period of the constituent elements in the periodic table were classified according to the atomic sizes of the BMGs discovered to date.
Abstract: Bulk metallic glasses (BMGs) have been classified according to the atomic size difference, heat of mixing (� H mix ) and period of the constituent elements in the periodic table. The BMGs discovered to date are classified into seven groups on the basis of a previous result by Inoue. The seven groups are as follows: (G-I) ETM/Ln-LTM/BM-Al/Ga, (G-II) ETM/Ln-LTM/BM-Metalloid, (G-III) Al/Ga-LTM/BMMetalloid, (G-IV) IIA-ETM/Ln-LTM/BM, (G-V) LTM/BM-Metalloid, (G-VI) ETM/Ln-LTM/BM and (G-VII) IIA-LTM/BM, where ETM, Ln, LTM, BM and IIA refer to early transition, lanthanide, late transition, group IIIB–IVB and group IIA-group metals, respectively. The main alloying element of ternary G-I, G-V and G-VII, ternary G-II and G-IV, and ternary G-VI BMGs is the largest, intermediate and smallest atomic radius compared to the other alloying elements, respectively. The main alloying element of ternary BMGs belonging to G-I, G-V, G-VI and G

2,983 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarize the recent developments in the synthesis, structural characterization, properties, and applications of amorphous and nanocrystalline soft magnetic materials, including: kinetics and thermodynamics, structure, microstructure, and intrinsic and extrinsic magnetic properties.

1,453 citations