Influence of indenter geometry on the nanoindentation-induced plasticity evolution in bulk metallic glasses

Abstract

Since bulk metallic glass (BMG) is known to exhibit deformation in an approximately elastic-perfectly-plastic way (without clear work-hardening) and possibly there is no indentation size effect (which is typically explained by the activities of crystalline defect, i.e. dislocations) due to the absence of long-range ordered structure, it can be considered as a good material for analyzing the influence of the indenter geometry on indentation behavior based on classical contact mechanics theories. With this in mind, here we explored systematically the influence of indenter geometry on the nanoindentation-induced elastic/plastic deformation of BMGs through nanoindentation experiments with a series of triangular pyramidal indenters having different centerline-to-face angles (in the range 35.3° to 70°) as well as various spherical indenters having different radii (in the range 550 nm to 100 micro-meter). The mechanical responses from spherical indentations (which can induce the sequential development of stresses and strains under the indenter during indentation) were carefully compared with those from geometrically self-similar sharp indentations (whose representative stress-strain field under the indenter is only dependent on indenter angle, if no indentation size effect). Results are discussed in terms of the evolution of the plasticity in the materials during nanoindentation.