Test environments and mechanical properties of Zr-base bulk amorphous alloys
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TRODUCTION
METALLIC glasses with amorphous structures were first synthesized in 1960.[1] In order to achieve an amorphous state, extremely high cooling rates (.106 K/s) were required at that time; as a result, only thin-section materials (,,0.1 mm) could be produced. Since metallic glasses possess many attractive properties for structural and functional uses, considerable efforts have been devoted for the past 3 decades to the synthesis of metallic glasses with higher glass-forming ability and lower critical cooling rates. The synthesis of metallic glasses in a bulk form (with thickness .1 mm) was successfully achieved in Ni40Pd40P20 alloys by Chen[2] in 1976. Substantial progress on the development of new bulk amorphous alloys (BAA) containing no noblemetal elements (such as Pd, Pt) with a high glass-forming ability has been made only in recent years. Since 1989, the year when BAAs based on La-Al-TM (where TM 5 transition-metal elements such as Ni, Cu, and C.T. LIU, Group Leader, L. HEATHERLY and J.A. HORTON, Research Staff Members, D.S. EASTON, Consultant, C.A. CARMICHAEL and J.L. WRIGHT, Technologists, and J.H. SCHNEIBEL and M.H. YOO, Senior Staff Members, are with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115. C.H. CHEN, Group Leader, is with the Life Sciences Division, Oak Ridge National Laboratory. A. INOUE, Professor, is with the Institute for Materials Research, Tohoku University, Sendai, 980-8577 Japan. This article is based on a presentation made at the ‘‘Structure and Properties of Bulk Amorphous Alloys’’ Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory. METALLURGICAL AND MATERIALS TRANSACTIONS A
Fe) were first discovered,[3] a number of BAAs with critical cooling rates ,103 K/s have been synthesized in multicomponent alloy systems. The stable metallic glass alloy systems bearing no noble-metal elements include La-Al-TM,[3,4] ZrAl-TM,[5] Zr-Ti-Al-TM,[6] Ti-Zr-TM,[7,8] Ti-Zr-TM-Be,[9,10] and Fe-(Al,Ga)-(P, B, C, Si) compositions.[11,12] Characterization of the atomic arrangement and physical and thermal properties of these BAAs reveals that their high glass-forming ability is related to several metallurgical factors.[8,13–16] First, these BAAs usually contain many elements, ≥3 elements, which results in increased glass-forming ability by increasing the configurational entropy of supercooled liquid phases. Second, the constituent elements have a large difference in atomic size, usually ≥12 pct, thus limiting the solubility of these elements in crystalline states and packing atoms, efficiently resulting in a lowering of the ground-state energy of supercooled liquid phases. Third, BAAs should possess negative heats of mixing, but no single intermetallic
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