New Bulk Metallic Glasses for Applications as Magnetic-Sensing, Chemical, and Structural Materials
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Glasses for Applications as Magnetic-Sensing, Chemical, and Structural Materials
Akihisa Inoue and Nobuyuki Nishiyama Abstract Since 1988, it has been demonstrated that metallic glasses can be made in bulk form with diameters larger than several millimeters. At present, several alloy systems with maximum diameters for glass formation exceeding 1 cm are known. As a result, Zr-, Ti-, Fe-, Co-, Ni-, and Cu-based bulk metallic glasses (BMGs) are already in use for magnetic-sensing, chemical, and structural applications. In this article, recently developed BMGs with critical diameters of more than 1 cm are summarized, and some of their industrial applications are reviewed.
Introduction At least since 1988, it has been known that metallic glasses can be directly made in bulk form by solidifying the melt at relatively low cooling rates. Unfortunately, such alloys with high glass-forming ability (GFA) were limited to La-,1 Mg-,2 Zr-,3,4 or Pd-based5,6 systems. Recently, the critical diameter Dc for glass formation (i.e., the maximum diameter of a rod that can be cast fully glassy) has exceeded 1 cm for a wider variety of alloy systems such as those based on Fe,7 Co,8 Ni,9 or Cu,10 resulting in significantly increased engineering importance for bulk metallic glasses (BMGs). The recently developed BMGs exhibit not only high GFA but also unique engineering characteristics11,12 and consequently are expected to be applied much more widely than the BMGs developed earlier. Typical industrial applications are: (1) magnetic applications such as linear actuators, magnetic cores, choke coils, and high-frequency magnetic-shielding sheets;
(2) chemical applications such as fuel-cell separators; and (3) structural applications such as sporting goods, precision optical parts, precision gears for micromotors, diaphragms for pressure sensors, tubes for Coriolis mass flowmeters, aircraft parts, automobile valve springs, and so on. In this article, recently developed BMGs with Dc > 1 cm are summarized, and a review is given of their industrial applications, some of which are under development for commercialization in the near future.
Recent Progress in Developing Fe- and Co-Based BMGs Adding a small amount of niobium increases the stability of the supercooled liquid for conventional glassy (Fe, Co, Ni)(B, Si) alloys, leading to BMG formation with diameters of up to 5 mm by coppermold casting.13 Furthermore, the same alloy, when treated with a B2O3 flux, provides a BMG with a diameter of 7.7 mm.14 This BMG exhibits good soft-magnetic
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properties: saturation magnetization Js = 1.13 T; coercivity Hc < 20 A/m at room temperature; and Curie temperature Tc = 732 K.14 An Fe65.5Cr4Mo4Ga4P12B5.5C5 BMG with a diameter of 4 mm, prepared by flux-melting and water-quenching,15 exhibits Hc = 0.4 A/m and maximum relative permeability µmax = 280,000.15 Recently, a small addition of lanthanide metal to the Fe-Cr-Mo-metalloid system enhanced its GFA; Fe48Cr16Mo14C15B6Er2 bulk metallic glass ha
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