On simultaneous enhancement in local yield strength and plasticity of short-term annealed bulk metallic glasses

• Both local strength and plasticity of a BMG increase with increasing fictive temperature. • Plasticity of BMG examined using number of pop-ins and shear bands. • Statistics of pop-in is analyzed to get activation parameters for STZs. • STZ to shear band transition is modeled considering evolving free volume. The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at different fictive temperatures ( T f ) are studied. To probe the size and distribution of microscopic carriers of plasticity, spherical-tip nanoindentation and microindentation are employed. With nanoindentation, events signifying the departure from Hertzian elastic contact, which manifest as pop-ins in the load-displacement response and correspond to incipient plasticity, are recorded and analyzed. Results indicate that with increasing T f , the incipient plastic event and the number of subsequent pop-ins increases. Using statistical analysis of the scatter in strength, the activation parameters for shear transformation zones (STZs) in all specimens are determined. By considering the linear accumulation of STZs to form a shear band, the increase in shear yield strength along with plasticity, with increasing T f , is explained.