Interatomic potential to predict the binary metallic glass formation
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Interatomic potentials are constructed for eight representative binary metal systems covering various structural combinations and thermodynamic characteristics. On the basis of the constructed interatomic potentials, molecular dynamics simulations reveal that the physical origin of metallic glass formation is the crystalline lattice collapsing while solute atoms are exceeding the critical value, thus determining two critical solid solubilities for the system. For a binary metal system, the composition range bounded by the two determined critical solid solubilities is therefore defined as its intrinsic glass-forming range, or quantitative glass-forming ability. I. INTRODUCTION
The first Au75Si25 amorphous alloy, namely metallic glass, was obtained by Duwez et al. in 1959 by liquid melt quenching (LMQ),1 and since then, LMQ has been used to produce a great number of metallic glasses in the binary metal systems.2,3 Since the late 1980s, researchers have found some multicomponent metal systems (3–5 elements), in which LMQ could readily produce the socalled bulk metallic glasses (BMGs), e.g., with a cooling speed of 100 K/s, the size of the obtained metallic glasses could be in a magnitude of centimeter.4–6 Consequently, BMG has become a hot objective due to its scientific significance as well as to its great potential for hi-tech applications.7,8 Naturally, one of the most important scientific issues in the field of metallic glasses is to establish a relevant theory capable of predicting the glass-forming ability (GFA) of an alloy system, i.e., predicting in which system and in which exact composition range(s), metallic glasses could likely be obtained. In the early stage, much attention was focused on the binary metal systems and, based on LMQ data, some empirical and thermodynamic criteria/rules have been proposed, e.g., the well-known deep eutectic criterion, atomic size difference criterion, etc. Accordingly, the binary metal systems have been classified, depending on obtainable or not by LMQ, into glass-forming and nonglass-forming systems, respectively.9–14 It is known that in the LMQ, the initial state is a liquid melt of an alloy and its corresponding liquid state (or disordered state) of the alloy is frozen on a fast liquid-to-solid transition, resulting in forming the metallic glass. Apparently, comelting of the constituent metals is a prerequested condition for LMQ to produce metallic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0109
976
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 5, May 2010 Downloaded: 25 Mar 2015
glasses. It follows that those equilibrium miscible binary metal systems, which are frequently characterized by negative heat of formation (DHf),15 could possibly be of glass-forming systems, whereas those equilibrium immiscible binary metal systems frequently characterized by positive DHf are definitely nonglass-forming systems, because the immiscible metals could not be comelted to form any alloy. In fact, the equilibriu
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