Cu–Zr and Cu–Zr–Al clusters: Bonding characteristics and mechanical properties

We present density functional theory (DFT) calculations results on two representative clusters (Cu7Zr6 and Cu10Zr5) and their interconnections (touching and interpenetrating). The choice of these clusters and their combinations is dictated from previous molecular dynamics (MD) simulations results on the Cu60Zr40 model metallic glass (MG) in which they were found to be the most abundant microstructural units. In addition, aiming in gaining inside on the experimental findings referring to properties improvement upon small Al additions in the CuZr MGs, we performed calculations for the same systems in which Al substitutional atoms were incorporated into the clusters. In all cases the electronic structures were analyzed and the corresponding bonding characteristics were deduced. Moreover, in order to reveal the electronic modifications these systems subsist under mechanical deformation, we performed non-equilibrium calculations by applying tensile solicitations and we deduced the basic alterations that are responsible for the systems’ responses. It turns out that Al has elemental bonding preference; its presence in the clusters and in their interconnections alters significantly their electronic structure by introducing new low-energy states, while significant charge transfer occurs upon mechanical deformation. The present results are in line with the available experimental findings and provide inside on the fundamental issues that are related with the improvement of the glass forming ability and of the mechanical properties in the systems that contain small Al additions.