Extreme rejuvenation of a bulk metallic glass at the nanoscale by swift heavy ion irradiation

Abstract

Swift heavy ions can be used as a tool to tune material properties by generating high aspect ratio, nanometric trails of defects, or new disordered phases. This work explores different aspects of using this tool for rejuvenating and enhancing plasticity in bulk metallic glasses. An amorphous alloy with a nominal composition of Pd40Ni40P20 was irradiated with GeV-accelerated Au ions. Irradiation-induced out-of-plane swelling steps up to approximately 100 nm in height are measured at the boundary between irradiated and non-irradiated areas. Changes of the relaxation enthalpy have been investigated using differential scanning calorimetry. Low-temperature heat capacity measurements substantiate an irradiation-induced increase of the boson peak height with increasing fluences. Accompanying transport measurements using radioactive Ag atoms as tracer also revealed increased diffusion rates in the irradiated samples dependent on the total fluence. Nano-indentation measurements show enhanced plasticity in the ion-irradiated glass which can be correlated with an increased heterogeneity as indicated by variable resolution fluctuation electron microscopy. The whole volume of the derived data substantiates a prominent enhancement of the excess volume in the solidified ion tracks and the irradiation-induced modifications are discussed and analyzed in the framework of strong glass rejuvenation within the nanometric ion tracks.