Enhanced ductility in Cu64Zr36 metallic glasses induced by prolonged low-energy ion irradiation: A molecular dynamics study

摘要

The irradiation induced variations in microstructure and mechanical properties of the Cu64Zr36 metallic glasses (MGs) are investigated via large-scale molecular dynamics simulations. The irradiation condition is modeled by sequential and prolonged collision cascades. The simulation results show a simultaneous decrease of the density and the fraction of Cu-centered full icosahedron (CCFI) clusters in the irradiated samples. This microstructural evolution induced by the prolonged irradiation is proposed to be responsible for the change of deformation mode of tested samples under uniaxial tensile loading. When increasing the irradiation dose, the ultimate tensile strength of MG samples decreases gradually, while their deformation mechanism switches from localized shear banding to ductile necking and finally to ideally plastic flow, enhancing the MG ductility. Careful atomic-scale examinations on the initiation and development of shear transformation zones (STZs) are carried out for a better understanding of the irradiation-induced ductility enhancement in MGs. Two related effects of the irradiation are unveiled. On the one hand, the irradiation releases the stored strain energy by promoting the STZ activation within the MG matrix. On the other hand, the irradiation damages restrain the propagation of shear band through the innovatively proposed two-unit "STZ-vortex" mechanism. Under the combined effect of these two mechanisms, the low-temperature ductility of irradiated MGs is improved and the brittle-like failure driven by single shear banding is prevented. (C) 2021 Elsevier B.V. All rights reserved.