Effects of cooling rate on the atomic structure of Cu64Zr36 binary metallic glass

Abstract

In this study, molecular dynamics simulations based on the embedded atom model (EAM) potentials were carried out to investigate influences of cooling rate on the ordered atomic structure, especially icosahedral short- and medium-range orders (ISRO and IMRO) in the Cu64Zr36 metallic glass (MG). It is found that potential energy of the system is strongly dependent on the cooling rate during the rapid solidification, and so does the glass transition temperature (Tg) which rises with increasing cooling rate. Both Honeycutt-Anderson bond pair and Voronoi polyhedra analyses indicate that icosahedral clusters are prominent in the Cu64Zr36 MG and the population of icosahedral polyhedra increases with decreasing cooling rate. The size of IMROs constructed by ISROs via the linkage of vertex-, edge-, face-, and intercrossed-shared atoms becomes larger as the cooling rate and temperature descend. The structural evolution with temperature manifests that the development of icosahedral ordering is the structural origin of the glass transition of the modeled alloy. Moreover, we found that the major structural units in the Cu64Zr36 MG are Cu8Zr5 and Zr6Cu10 polyhedra for Cu- and Zr-centered clusters, respectively, which are different from the main competing crystalline phase upon cooling. The good glass-forming ability of the modeled alloy is originated from the chemical and structural discrepancy between these main clusters and the competing phase, which effectively retards the crystal nucleation in the Cu64Zr36 alloy during rapid solidification.