Evolution of the Mechanical Properties of Ti-Based Metallic Glass During Depth-Sensing Load–Unload Nanoindentation Cycles

The mechanical behaviour of Ti-based bulk metallic glass during consecutive load–unload nanoin-dentation cycles, using progressively larger forces, is investigated. Indentation cycles allow eval-uating the contact stiffness and, therefore, the hardness and Young’s modulus as a function of the penetration depth. The indentation hardness shows a gradual decrease as the applied load increases, evidencing the occurrence of an indentation size effect. An increase of contact stiffness is also observed during the indentation cycling process, an effect which is accompanied with a slight reduction of the Young’s modulus. These observations are consistent with the presumption that metallic glasses become structurally modified during the course of nanoindentation experi-ments. In particular, a deformation-induced increase in the amount of free volume occurs within the amorphous structure, leading to a concomitant mechanical softening.