Unusual He-ion irradiation strengthening and inverse layer thickness-dependent strain rate sensitivity in transformable high-entropy alloy/metal nanolaminates: A comparison of Fe50Mn30Co10Cr10/Cu vs Fe50Mn30Co10Ni10/Cu.

• The Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs exhibit better irradiation resistance due to duplex HEA layers. • The irradiation hardening trend of Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs is contrary to conventional bimetal nanolaminates. • The characters of He bubbles strongly influence the mechanical response of both Fe 50 Mn 30 Co 10 Cr 10 /Cu and Fe 50 Mn 30 Co 10 Ni 10 /Cu NLs. • The irradiated Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs display unusual size-dependent SRS m which is attributed to He bubbles on dislocation nucleation and motion. In this work, we prepare transformable HEA/Cu nanolaminates (NLs) with equal individual layer thickness (h) by the magnetron sputtering technique, i.e., Fe 50 Mn 30 Co 10 Cr 10 /Cu and Fe 50 Mn 30 Co 10 Ni 10 /Cu, and comparatively study He-ion irradiation effects on their microstructure and mechanical properties. It appears that the as-deposited HEA/Cu NLs manifest two size h -dependent hardness regimes (i.e., increased hardness at small h and hardness plateau at large h), while the He-implanted ones exhibit monotonically increased hardness. Contrary to the fashion that smaller h renders less irradiation hardening in bimetal NLs, the Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs manifest the trend that smaller h leads to greater irradiation hardening. By contrast, the Fe 50 Mn 30 Co 10 Ni 10 /Cu NLs exhibit the maximum irradiation hardening at a critical h = 50 nm. Below this critical size, smaller h results in lower radiation hardening (similar to bimetal NLs), while above this size, smaller h results in greater radiation hardening (similar to Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs). Moreover, these transformable HEA/Cu NLs display inverse h -dependent strain rate sensitivity (SRS m) before and after He-ion irradiation. Nevertheless, compared with as-deposited samples, the irradiated Fe 50 Mn 30 Co 10 Cr 10 /Cu NLs display reduced SRS, while the irradiated Fe 50 Mn 30 Co 10 Ni 10 /Cu NLs display enhanced SRS. Such unusual size-dependent irradiation strengthening and inverse h effect on SRS in irradiated samples were rationalized by considering the blocking effects of He bubbles on dislocation nucleation and motion, i.e., dislocations shearing or bypassing He bubbles. [ABSTRACT FROM AUTHOR]