Structural Heterogeneity in Metallic Glasses—Dependence on Various Parameters and Effect on Plastic Flow

The ability to modify the atomic-scale structure of metallic glasses by processing allows to tailor their mechanical properties. To fully use this ability, it is important to understand local ordering and density fluctuations, both of which manifest as structural heterogeneity. For example, deformation mechanisms are strongly affected by the details of the structure, transforming from homogeneous deformation for small deformation volumes to inhomogeneous deformation with stress localization when larger deformation volumes are in play. This transformation is mainly driven by the ability of the material to localize stress, which is affected by both the degree of structural heterogeneity as well as by the free volume available to release externally applied stress. In this talk, we first study heterogeneity on the nanometer and micron scale in samples made from Pt_57.5Cu_14.7Ni_5.3P_22.5 by thermoplastic forming followed by an annealing procedure that sets their fictive temperatures <i>T</i>_f. Atomic force microscopy imaging revealed both topography as well as the sample’s stiffness, modulations of which reflect structural inhomogeneity. The results show that samples featuring <i>T</i>_f’s close to the material’s glass transition temperature <i>T</i>_g of 235 °C are more homogeneous than samples with <i>T</i>_f’s that are lower or higher, a trend that is markedly different from the one found for the absolute values of the average stiffness, which monotonically increases for lower<i> T</i>_f’s. The experimental results are then being discussed in the light of recent molecular dynamic simulations.