Development and Characterization of Low-Density Ca-Based Bulk Metallic Glasses: An Overview
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INTRODUCTION: CLASSIFICATION AND MAIN FEATURES OF Ca-BASED BULK METALLIC GLASSES
NEW metallic alloys with exceptional glass forming ability (GFA), which can remain amorphous after solidification at relatively low cooling rates typical of conventional metal mold casting, open new opportunities both for fundamental studies and technological advances. High thermal stability, exceptional mechanical and physical properties, as well as the ability to be plastically formed in the supercooled liquid state make bulk metallic glasses (BMGs) attractive for engineering applications. Over the last two decades, a number of BMGs based on Pd, Zr, rare earth metals, Fe, Cu, Ni, Mg, and some other elements have been produced, and different methods have been proposed to guide the discovery of new glasses with better GFA.[1–4] The Ca-based BMGs are a relatively new class of amorphous alloys. The first Ca-based BMGs were reported by Amiya and Inoue in 2002.[5,6] They produced two ternary glasses, Ca57Mg19Cu24 and Ca60Mg20Ag20, with a maximum diameter of 4 mm and a quaternary Ca60Mg20Ag10Cu10 with a maximum diameter of 7 mm. During the following years, a number of Ca-Mg-Zn, Ca-Mg-Cu, Ca-Mg-Al, Ca-Al-Cu, Ca-Mg-
O.N. SENKOV, Senior Scientist, is with UES, Inc., Dayton, OH 45432. Contact e-mail: [email protected] D.B. MIRACLE, Senior Scientist, is with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433. V. KEPPENS, Associate Professor, and P.K. LIAW, Professor, are with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA. This article is based on a presentation given in the symposium entitled ‘‘Bulk Metallic Glasses IV,’’ which occurred February 25– March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee. Article published online October 19, 2007 1888—VOLUME 39A, AUGUST 2008
Zn-Cu, Ca-Mg-Al-Zn, Ca-Mg-Al-Cu, Ca-Y-Mg-Cu, Ca-Mg-Al-Zn-Cu, Ca-Y-Mg-Zn-Cu, and Ca-Mg-AlAg-Cu BMGs with thicknesses up to 10 mm were reported by Senkov et al.[4,7–12] Approximately, at the same time, Park and Kim[13] produced a Ca65Mg15Zn20 alloy, which was fully amorphous in up to 15-mm diameter cross sections. They also developed several other Ca-Mg-Zn amorphous alloys.[14] Guo et al.[15] reported on Ca-Al-Cu, Ca-Al-Ag, and Ca-Al-Mg amorphous alloys with a maximum diameter of 2 mm and Ca-Mg-Al-Cu and Ca-Mg-Al-Ag glasses with a maximum diameter of 4 mm. All of these Ca-based BMGs can be described by the formula[4,7] CaA ðY,LnÞB ðMg,SnÞC ðAl,Ag; Ga,ZnÞD ðCu,NiÞE
½1
with A = 40 to 70, B = 0 to 30, C = 0 to 30, D = 0 to 35, E = 0 to 35, and A + B + C + D + E = 100. A strong topological basis[4,16–20] exists for the compositions represented in Eq. [1], and a structural model has recently been developed following these background developments.[21] The breadth of Eq. [1] and the results just cited indicate that many Ca-based alloys are good glass formers. A graphical pres
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