Mechanism of local hardening in metallic glass during He ion irradiation

When exposed to He radiation, metallic glasses (MGs) often undergo a unique transformation and mechanical evolution, unlike their crystalline counterparts. However, the relationship between He bubble evolution and the mechanical response is largely unknown. Here, a localized hardness change along ion irradiation direction was discovered under the condition that He ion irradiation does not induced nanocrystallizaiton. The location of the localized hardening peak shifted to the right, and this was accompanied by nucleation and growth of the He bubbles as the fluence increased. Besides, coalescence and overlap of the He bubbles were observed in the central of the bubble layer at the highest fluence. The localized hardness change was quantified by a model based on the He bubbles size and density. The results of this study provide insights into the effect of He bubbles on mechanical evolution and pave the way for designing MGs suitable for the nuclear industry.