How Can a Minor Element Added to a Binary Amorphous Alloy Simultaneously Improve the Plasticity and Glass Forming Ability

Hong-Kyu Kim, Mirim Lee, Kwang-Ryeol Lee, Jae-Chul Lee
 

Minor elements, when added to binary amorphous alloys in small percentages, can often lead to significant improvements in both the plasticity and glass-forming ability (GFA) of the alloys. Considering that plasticity and GFA are the two contrasting properties dependent on short-range orders (SROs) of differing degrees, this experimental observation at first seemed paradoxical when considered from an SRO viewpoint. In this study, comparative studies on the amorphous alloys, Cu₅₀Zr₅₀ and Cu_47.5Zr_47.5Al₅, were performed using experiments and simulations to elucidate how these two apparently mutually exclusive properties can be realized at the same time. Using molecular dynamics (MD) simulations, we resolved the local structures of Cu₅₀Zr₅₀ and Cu_47.5Zr_47.5Al₅ in terms of icosahedral medium-range orders (MROs). In addition, the role of the minor element (Al) on the formation of the icosahedra and their medium-range structures during cooling, as well as their disordering behavior during subsequent plastic relaxation, was clarified.