High entropy state of orientationally-disordered clusters in Zr-based bulk metallic glass

Akira Takeuchi, Makoto Ogata, Akihisa Inoue

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

A phase transformation of a metastable Zr2Ni intermetallic crystalline phase to vitrify was studied with molecular dynamics (MD) simulations based on a plastic crystal model (PCM), which utilizes the orientational disorder of molecules of plastic crystals in a class of soft matter. The simulation results showed that computational operations in MD-PCM for the random rotations of the clusters in the crystalline phase around their center of gravity and subsequent annealing lead to form a dense random packing structure from the metastable Zr2Ni phase. These randomly-rotated clusters provide high degrees of freedom in terms of atomic positions, which results in enhancing the glass-forming ability of the alloy. The critical fraction of the number of rotated clusters for forming the glassy phase (fc R) is evaluated to be 0.75-0.80. Thus, the critical fraction of the number of un-rotated clusters (fc U=1-fc R) is close to the critical concentration of site percolation for metallic materials. The mechanism of the metastable Zr2Ni phase to vitrify with increasing f R was analyzed with a concept of communal entropy in the free volume theory with solid- and liquid-like cells proposed by Cohen and Grest. The MD-PCM for the metastable Zr2Ni phase suggests that Zr-based bulk metallic glass (BMG) can be regarded as an alloy in a high rotation entropy state of clusters and that glass transition takes place by percolation of the nuclei of a liquid-like glassy phase.

Original languageEnglish
Pages (from-to)87-96
Number of pages10
JournalProgress in Natural Science: Materials International
Volume20
Issue number1
DOIs
Publication statusPublished - 2010 Nov

Keywords

  • Communal entropy
  • Metallic glass
  • Molecular dynamics simulation
  • Percolation
  • Plastic crystal

ASJC Scopus subject areas

  • Materials Science(all)

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