Indentation creep dynamics in metallic glasses under different structural states

Abstract

In this study, the effects of the structural energy states (as-cast and relaxed) of Zr50Cu40Al10 metallic glass were investigated using depth-sensing nanoindentation. In terms of cooperative shear model, we performed experimental characterization of shear transformation zone for plastic flow of metallic glass. The shear transformation zone volume of the relaxed metallic glass is larger than that of as-cast one, while the strain rates sensitivity displays the opposite tendency. The plastic deformation in the creep stage of nanoindentation originates from the “delayed plasticity” inherited from the loading process. The creep depth shows strain rates and microstructural states dependence. The characteristic relaxation time and creep depth limit were determined by fitting the displacement versus time curves with Kelvin model are employed to characterize the creep dynamics of metallic glasses. It was found that the softening effects in the plastic deformation originates from the collective movements of the deformation carriers (shear transformation zones). The different softening behaviors were discussed from the perspective of soft zones in the framework of the free volume model. Our experimental as well as the theoretical analysis deepens the fundamental understanding of plasticity deformation mechanism in metallic glasses.