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Cooling rates dependence of medium-range order development in Cu64.5Zr35.5 metallic glass

TitleCooling rates dependence of medium-range order development in Cu64.5Zr35.5 metallic glass
Publication TypeJournal Article
Year of Publication2015
AuthorsZhang, Y, Zhang, F, Wang, CZ, Mendelev, MI, Kramer, MJ, Ho, KM
JournalPhysical Review B
Date Published02
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000351774900004
Keywordsamorphous-alloys, cu-zr alloys, local order, model, packing, simulation, structural behavior, supercooled liquid, transition

The atomic structure of metallic glasses (MGs) plays an important role in their properties. Numerous molecular dynamics (MD) simulations have revealed icosahedral short-range order (ISRO) as a dominant motif in Cu-Zr metallic glasses. However, the cooling rates utilized in most of the MD simulations (usually on the order of 10(10-13) K/s) can be too high to allow the structure to relax into the actual structures. By performing a long sub-T-g annealing of the Cu64.5Zr35.5 alloy model at 700 K up to 2.0 mu s using MD simulations, we systematically address the evolution of medium-range order (MRO) as the cooling rates in MD simulations approach the experimental cooling rates (usually 10(3-6) K/s). By reducing the effective cooling rates to as low as 2.8 x 10(7) K/s, we found a significant enhancement of the ISRO and Bergman-type MRO. Comparing to the widely used face-, edge-, or vertex-sharing icosahedra, we propose that the Bergman-type MRO is a much more unambiguous metric to characterize the MRO in Cu-Zr MGs. By analyzing the network formed by interpenetrating icosahedra using the graphical theory, we show that the degree of interpenetration of the icosahedra centers increases with decreasing cooling rates. The network becomes aggressively assortative, indicating that higher degree nodes tend to cluster and form backbones in the MG. All these results show that the networks in the models prepared using lower cooling rates strongly deviate from a stringlike morphology.

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Structures and Dynamics