Akihisa INOUE

WPI, Advanced Institute for Materials Research, Tohoku University, Japan

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Title: Development and Applications of Bulk Metallic Glasses

In the late 1980's, we found a number of metallic glassy alloys exhibiting a large supercooled liquid region before crystallization in multi-component La-, Mg- and Zr-based systems. We also noticed that the stabilization phenomenon of their supercooled liquid enabled us to fabricate bulk metallic glasses (BMGs) with critical diameters above several millimeters by slow cooling processes. Following these pioneering developments, the fabrication of BMG was confirmed in another Zr-based alloy by Caltech group in 1993. Since then, much attention has been paid to BMGs because of their novelties in basic science and engineering aspects. At present, new materials science and engineering fields on BMGs have been established. Focusing on new achievements obtained for the past several years, we fabricated some new BMGs with unique characteristics based on technologically-important transition metals, such as Zr-, Ti-, Fe-, Co-, Ni- and Cu-based alloys. We have also succeeded in achieving the maximum diameter for glass formation as large as 30 mm for Zr- and Cu-based systems, 12 mm for Ti-based system, 18 mm for Fe-Co-based system and 20 mm for Ni-based system, even employing the copper mold casting technique. These large size BMGs possess nearly the same fundamental properties as those for the BMGs with diameters of millimeters. We have further reported that BMGs with diameters above 10 mm are formed in Zr-Al-Ni-Cu system with Zr compositions higher than 65 at% and these Zr-rich BMGs exhibit high Poisson's ratio, high ductility, high fracture toughness, high fatigue strength and high stability of mechanical properties to annealing-induced embrittlement. The new Ti-based BMGs without allergic and toxic elements also exhibit good compatibility to bio-tissues. Application stages of BMGs in Fe-, Co-, Ti- and Zr-based systems have been advanced in the following parts and devices, e.g., choke coil, power inductor, electro magnetic shielding, magnetic and position sensors, micro-geared motor, pressure sensor, Colliori flow meter, surface coating layer, precise polishing medium, magnetic and structural parts in electric magnetic control-type spring drive watches, medical operation instruments and so forth.