Composition-dependent stability of the medium-range order responsible for metallic glass formation
The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. We focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. Our results show that a Bergman-type motif with crystallization-resisting icosahedral symmetry is energetically most favorable in the composition range 0.63 < xCu < 0.68, and is the underlying motif for one of the three optimal glass-forming ranges observed experimentally for this binary system (Li et al., 2008). This work establishes an energy-based methodology to evaluate specific medium-range structural motifs which compete with stable crystalline nuclei in deeply undercooled liquids.
This is a manuscript of an article published as Zhang, Feng, Min Ji, Xiao-Wei Fang, Yang Sun, Cai-Zhuang Wang, Mikhail I. Mendelev, M. J. Kramer, Ralph E. Napolitano, and Kai-Ming Ho. "Composition-dependent stability of the medium-range order responsible for metallic glass formation." Acta Materialia 81 (2014): 337-344. DOI: 10.1016/j.actamat.2014.08.041. Posted with permission.