Metallic elements having negative enthalpies of mixing tend to form characteristic local atomic clusters. In this review, we use the structural information in the first nearest neighbour shell level, or first-shell atomic cluster, to derive the composition rules of two types of complex alloy phases, quasicrystals and bulk metallic glasses, both being composed of elements with negative enthalpies of mixing. We first show the composition phenomena in quasicrystal-forming systems, where major composition rules such as cluster line, electron concentration and atomic size criteria are derived. Then we analyse the composition rules of bulk metallic glasses using the very same approaches. Finally, we summarize their common composition rules into more general rules and basic theories.
Composition optimization for the largest glass-forming ability has been performed in the Zr-Al-Ni(Co) systems in this investigation. Two guiding criteria, termed respectively the e/a-constant criterion and the e/a-variant criterion, are applied. They are incarnated into the e/a = 1.5 composition line and the Zr 9 Ni(Co) 4 -Al composition line. Bulk metallic glasses are obtained by suction casting alloy melts of compositions within an e/a span of 1:3$1:5, with their thermal stabilities and glass forming abilities being increased with increasing e/a. The intersecting point of the two lines gives the composition Zr 53 Al 23:5 Ni(Co) 23:5 with the largest glass-forming ability.
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