Icosahedral coordination and atomic rearrangements in deformed metallic glasses

Numerical simulations were employed to explore local atomic rearrangements taking place in metallic glasses undergoing shear deformation. The study focuses in particular on icosahedrally coordinated atoms. The number of such atoms starts decreasing during the elastic deformation stage, undergoes a definite drop at yield and then slightly decreases in the flow regime. The atoms with icosahedral coordination are shown to form fractal clusters. Their number, size and fractal dimension depend on the quenching rate and vary with the degree of deformation. All of these quantities exhibit different behaviours in the different elastic deformation, yield and plastic deformation stages. The analysis of their behaviour indicates that the cluster size affects the probability of a given cluster being involved in local rearrangements. In particular, icosahedrally coordinated atoms belonging to large clusters are preferentially involved in rearrangements taking place during the elastic deformation stage.