Full icosahedra dominate local order in Cu64Zr34 metallic glass and supercooled liquid

• Published in: Acta materialia 2014-05, Vol.69, p.343-354
• Main Authors: Ding, Jun, Cheng, Yong-Qiang, Ma, Evan
• Format: Article
• Language: English
• Subjects: Amorphous materials; Applied sciences; Copper base alloys; Cu–Zr; Evolution; Exact sciences and technology; Full icosahedra; Liquids; Metallic glasses; Metals. Metallurgy; Order disorder; Polyhedrons; Supercooled liquids; Zirconium
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2014.02.005

Extensive molecular dynamics simulations were carried out to monitor the development of icosahedral order in Cu64Zr34 liquid and metallic glass (MG). This study illustrates that at this Cu-rich Cu–Zr alloy composition, Cu-centered full icosahedra constitute the dominant and characteristic short-range-ordered coordination motif. The results for this model liquid/glass address five questions regarding the ordering of Cu-centered coordination polyhedral towards full icosahedra, including: (i) its evolution and extent during prolonged structural relaxation; (ii) the resulting reduction in potential energy and slowing-down of dynamics; (iii) the accompanying preference of a particular type of Zr-centered Kasper coordination polyhedra; (iv) the evolution and conversion of polyhedral connection schemes in the medium range; and (v) the formation and percolation of networks formed by interpenetrating connection of icosahedra to constitute a stiff backbone over extended range. Five related issues are also clarified, to: (i) differentiate full-icosahedra-based ordering from the generally favorable fivefold bonds; (ii) compare the Cu-based perspective with a Zr-centric view; (iii) systematically list the rationales behind focusing on icosahedral order for explaining the Cu64Zr34 MG/liquid properties; (iv) discuss other non-icosahedral ordering varieties; and (v) comment on the most liquid-like local environments. Taken together, the ten issues addressed set the stage for understanding structure–property relations in a category of amorphous alloys that can be characterized based on full-icosahedral ordering.