Influence of the loading rate on the indentation response of Ti-based metallic glass

The mechanical behavior of Ti-based metallic glass has been investigated by means of indentation experiments at different loading rates. Contrary to many crystalline materials, an increase of the loading rate causes a reduction of hardness, i.e., a mechanical softening. This effect is ascribed to deformation-induced creation of excess free volume, which is more pronounced for higher strain rates. The decrease of hardness is accompanied with an increase of the contact stiffness and a reduction of the reduced elastic modulus. Finite element simulations reveal that the mechanical response of this material can be described using the Mohr-Coulomb yield criterion. The changes in the nanoindentation curves with the increase of loading rate are well reproduced by decreasing the value of the Mohr-Coulomb cohesive stress. This result is consistent with the presumed enhancement of free volume.