Size- and ion-dose-dependent microstructural evolution and hardening in He-irradiated miscible Cu/Zr crystalline/crystalline nanolaminates

The microstructural features and hardness of He-irradiated miscible Cu/Zr crystalline/crystalline nanolaminates with a negative enthalpy of mixing were investigated at room temperature. The distribution of He bubbles within the Cu layers exhibits a high dependence on both layer thickness (h) and ion dose (Φ), while that at the Cu-Zr interfaces is only affected by ion dose. Compared with their as-deposited counterparts, the He-irradiated Cu/Zr nanolaminates tend to manifest radiation-induced solid-state amorphization (RSA), which was induced by ion beam mixing and initiated from crystalline interfaces. The size-dependent hardness of the as-deposited Cu/Zr nanolaminates is elucidated by a transition in the strengthening mechanism from the interfacial barrier strengthening mechanism to the confined layer slip of partials when h is increased. In the He-irradiated Cu/Zr samples, however, the size-dependent hardness is highly related to Φ. Under lower Φ a nonmonotonically h-dependent irradiation hardening is evident and is associated with a transition from irradiation hardening at large h (≥10 nm) to softening at small h (<10 nm), and the maximum hardening occurs at a critical value of h ≈ 25 nm. In contrast, under higher Φ the Cu/Zr nanolaminates merely display irradiation softening behavior, with the minimum softening at the critical value of h ≈ 25 nm. The underlying mechanisms are highlighted in terms of dislocation-bubble interactions and RSA. These findings indicate the effects of He ion dose and layer thickness on the He bubble distribution and the interface-mixing of Cu/Zr nanolaminates as well as provide thorough insight into how to tune the He ion dose to manipulate the mechanical response of nanolaminated FCC/HCP materials on a small scale.