Softening in an ultrasonic-vibrated Pd-based metallic glass

Abstract

The mechanical behavior of the Pd40Cu30P20Ni10 metallic glass after ultrasonic vibration was systematically investigated by nanoindentation. A notable softening after ultrasonic treatment was demonstrated by about 25% and 40% reduction of hardness and elastic modulus, respectively. The Maxwell-Voigt model was utilized to characterize the structure evolution during ultrasonic-assistant plastic deformation. Combined with differential scanning calorimeter experiments, it is found that the flow defects with shorter characteristic relaxation time activated under ultrasonic-frequency cycling loading benefits fast atomic diffusion with a low energy barrier, which eventually leads to the pronounced creep displacement, and thereby the large moldability at ambient temperature. This work might enlighten the structural origin for the plastic flow of metallic glasses under stress-assisted molding, imprinting as well as cold joining, which may help us in deeply understanding the defect activation mechanism in disordered systems.