Strain hardening and recovery in a bulk metallic glass under nanoindentation

Hardening and recovery phenomena, which have not been recognized in amorphous materials at room temperature before, were observed in a bulk metallic glass (BMG) using an instrumented nanoindentation. From designed cyclic experiments, we observed the hardness of the BMG increased each time when the sample was reloaded immediately after unloading and then gradually reduced to a stable value before the next unloading. This phenomenon was explained using a free-volume model for amorphous structure.