Size-dependent He-irradiated tolerance and plastic deformation of crystalline/amorphous Cu/Cu-Zr nanolaminates

Nanoindentation methodology was used to measure the hardness, strain rate sensitivity (SRS) and activation volume of Cu/Cu-Zr crystalline/amorphous nanolaminates (C/ANLs) with layer thickness (h) spanning from 2.5 to 150 nm before and after He ion-implantation at room temperature. It is interestingly to uncover that the ion radiation-induced devitrification (RID) occurs in the glassy Cu-Zr nanolayers, in which the nanocrystallites transit from the Cu₁₀Zr₇ intermetallics at large h to the fcc Cu-Zr solid solution at small h. Compared with the as-deposited Cu/Cu-Zr C/ANLs associated with monotonic increase in hardness and SRS (or a monotonic decrease in activation volume) with reducing h, the irradiated Cu/Cu-Zr manifested enhanced hardness in the form of two hardness plateau and an unexpected non-monotonic variation in SRS (similarly in activation volume). It was clearly unveiled that the SRS of irradiated Cu/Cu-Zr firstly decreased with reducing h down to a critical size of ∼50 nm and subsequently increased with further reducing h to ∼10 nm, below which a SRS m plateau emerges (The activation volume of irradiated Cu/Cu-Zr had exactly an opposite variation). These phenomena are rationalized by considering a competition between dislocation-interface and dislocation-bubble interactions. A thermally activated model based on the depinning process of bowed-out dislocations pinned by obstacles was employed to quantitatively account for the variation of SRS with h in Cu/Cu-Zr C/ANLs before and after radiation. Our findings not only provide fundamental understanding of the effects of radiation-induced defects on plastic characteristics of C/ANLs, but also offer guidance for their microstructure sensitive design for performance optimization at extremes.