Composition rule of bulk metallic glasses and quasicrystals using electron concentration criterion
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J.B. Qiang State Key Laboratory for Materials Modification and Department of Materials Engineering, Dalian University of Technology, Dalian 116024, People’s Republic of China
C.H. Wong and C.H. Shek Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong
C. Donga) State Key Laboratory for Materials Modification and Department of Materials Engineering, Dalian University of Technology, Dalian 116024, People’s Republic of China (Received 30 July 2002; accepted 11 December 2002)
This paper aims at establishing a number of electrons/atom (e/a)-based criterion for searching bulk metallic glasses (BMGs) and quasicrystals with large forming abilities in the Zr-based multicomponent alloy systems. After discussions on the diffraction characteristics corresponding to the Fermi surfaces–Brillouin zone interaction in the Zr-based Hume–Rothery phases, the Hume–Rothery matching rule is well explained when the effective e/a value of the matrix element Zr is taken as 1.5. The BMG- and quasicrystal-related phases are pointed out to be a family of nearly e/a-constant phases in a given alloy system. An e/a-constant criterion is then used to predict the ideal composition of the quasicrystals and BMGs in the Zr–Ti–Ni, Zr–Al–Ni, and Zr–Al–Ni–Cu systems, respectively. Nearly pure bulk Zr–Ti–Ni quasicrystals and a series of BMGs with glass-forming abilities greater than that of the known Zr65Al7.5Ni10Cu17.5 alloy are found.
I. INTRODUCTION
A Hume–Rothery phase is electronically stabilized when a pseudogap is formed across the Fermi level (EF). In such a case, the total kinetic energy of valence electrons would be reduced, thereby lowering the system energy. The Fermi surface–Brillouin zone (FS–BZ) interaction, denoted as 2kf ≈ kp, where kf is the momentum of electrons at the Fermi level and kp is the width of the Brillouin zone, is believed to be a mechanism directly related to the formation of the pseudogap at EF.1–3 The formation and stabilities of amorphous alloys as well as quasicrystals and their crystalline approximants follow a similar Hume–Rothery mechanism as discussed in the literature.4–8 The discovery of bulk metallic glasses (BMGs) and quasicrystals in the Zr-based and (Zr,Ti)-based multicomponent alloy systems9–13 evokes the investigation of a)
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J. Mater. Res., Vol. 18, No. 3, Mar 2003 Downloaded: 16 Mar 2015
the underlying principles governing the large forming abilities of these Hume–Rothery phases. On the basis of the aforementioned FS–BZ mechanism, their ideal compositions might correspond to specific electron/atom ratios (e/a). In ternary quasicrystal-forming systems, an e/a-constant phenomenon was revealed that the quasicrystal and its crystalline approximants share at nearly the same e/a values.14,15 An attempt has been subsequently carried out in the Al–Fe–Ni ternary system, and a precise prediction of the ideal compositions of ternary quasicrystals was reached.16 It is the
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