Prior studies on He ion irradiation-induced damage in several immiscible metallic nanolayer systems with incoherent interfaces show a prominent size effect on mitigation of radiation damage frequently. In general, the magnitude of radiation hardening and defect cluster density are both lower in smaller individual layer thickness (h) than in larger h, as interfaces can effectively reduce the density of radiation-induced defect clusters. This research shows, however, an opposite size-dependent strengthening behavior in He ion-irradiated immiscible coherent Cu/Co multilayers, i.e. films with smaller h have greater radiation hardening. Such unusual size-dependent strengthening could be explained via a transition of strengthening mechanisms from partial dislocation (before radiation) to full dislocation transmission (after radiation) across layer interfaces as a result of the formation of He bubbles at the layer interfaces. Furthermore, it is shown that, similarly to incoherent immiscible systems, a coherent interface in the immiscible system can also effectively reduce the population of radiation-induced defect clusters.
Bibliographical noteFunding Information:
X.Z. acknowledges financial support by NSF DMR-1304101. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the US Department of Energy under contract DE-AC52-06NA25396. Access to the microscopy and imaging center (MIC) at Texas A&M University is also acknowledged.
© 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
- He bubbles
- He ion irradiation
- Immiscible multilayers
- Radiation hardening
- Size effect