Incipient Plasticity and Shear Band Formation in Bulk Metallic Glass Studied Using Indentation

This study focuses on investigating certain aspects of deformation in bulk metallic glasses (BMGs) based on nanoindentaion and microindentation studies. Using a Berkovich indenter in nanoindentation, the incipient plasticity or early stages of deformation have been studied for a typical BMG, Vitreloy 1. From a critical analysis of the load-displacement curves, the initial displacement burst, often associated with the initiation of shear bands, was found to occur at a value close to the theoretical shear stress of the material. The deformation behavior below these indents, including the formation of shear bands, has been investigated by transmission electron microscopy. The evidence suggests structural changes associated with possible expansion of free volume within the shear bands, especially in the case of deformation under higher loads. Furthermore, while the possibility of nanocrystallization within the shear bands cannot be ruled out, the experimental results do not conclusively indicate the occurrence of such a phenomenon.