Effect of topologically close-packed clusters on glass-forming ability of rapidly supercooled MgCuY alloy

Abstract

The glass-forming ability (GFA) of metallic glasses can be enhanced by adding trace elements, but it is difficult to explain the reasons from microcosmic viewpoint due to the limitation of experimental conditions. Therefore, in order to reveal the effects of trace elements on GFA, the rapid solidification process of Mg65Cu(35-x)Yx (x = 5,10,15,20,25) ternary alloys are simulated by molecular dynamics (MD) in this paper, then the short- and medium-range order, thermodynamics and dynamics are investigated. The average atomic potential energy shows that the GFA becomes stronger monotonically with the increase of Y element. S433 and S544 can evolve into S555 with higher fivefold symmetry and packing density during solidification, which the topologically close-packed (TCP) clusters are mainly composed of S555. And the higher TCP clusters system has stronger GFA, because TCP clusters are easy to connect with each other to form large-sized nanoclusters, and the larger size nanoclusters have a smaller average displacement, which hinders the crystallization. As TCP atoms with slower dynamic characteristics than other atoms, the dynamics with higher Y element becomes slower with the increase of TCP clusters, and thus adding Y element plays a promoting role for GFA.