Interface-controlled mechanical properties and irradiation hardening in nanostructured Cr₇₅Al₂₅/Zr multilayers

As an efficient strategy to design accident-tolerant fuel (ATF) materials, nanostructured metallic multilayers (NMMs) have attracted significant research interest. In this work, Cr₇₅Al₂₅/Zr (CA/Zr) NMMs were prepared with equal individual layer thickness h spanning from 5 to 75 nm, and subjected to He⁺ implantation with a total fluence of 1 × 10¹⁷ ions cm⁻² at room temperature. With decreasing h, the interface changed from crystalline/crystalline to crystalline/amorphous along with size-driven strengthening to softening behavior of CA/Zr NMMs at the critical thickness h = 25 nm. The size-dependent hardness consists well with the evolution of the back stress with respect to h, which is elucidated by the statistical dislocation absorption propensity by the interface. Moreover, notable irradiation hardening emerges in the CA/Zr NMMs, which is caused by He bubble-dislocation interactions at large h and by the cooperation of He bubble hardening and increased back-stress hardening at small h. The hardness of both as-deposited and irradiated CA/Zr NMMs was quantitatively explained by dislocation models operative at different length scales.