On the subsurface deformation of two different Fe-based bulk metallic glasses indented by Vickers micro hardness

Bonded interface technique was employed to examine the nature of subsurface deformation during Vickers micro indentation in two iron-base bulk metallic glasses, (Fe0.9Ni0.1)77Mo5P9C7.5B1.5 (BMG-1) and Fe40Co8Cr15Mo13Y2C16B6 (BMG-2). Quantitative information such as the subsurface deformation zone size was recorded for indentation loads ranging from 200 to 5000 gr. The results showed that the BMG-2 specimens had an average hardness value higher than those observed in the BMG-1 specimens. The trends of the hardness vs. indentation load in the BMG-1 specimens were found to be related to the pressure sensitive index, while in the BMG-2 specimens, the cracking events and deformation-induced creation of free volume were responsible for the hardness tendency change. Observations of the deformation zones indicated that they deformed noticeably through two types of semi-circular and radial shear bands and the density of the radial shear bands was much more in the annealed specimens compared to the as-cast specimens. The relaxed and partially crystallized BMG-2 specimens exhibited cracking, ripple-like pattern as well as cracking and fragmentation, respectively. A simplified R = CP0.5 model was used to analyze the shear band zone size in the subsurface and specimens brittleness.