Abstract and subjects
Nanoindentation was used to measure hardness before and after room temperature He ion implantation on sputter-deposited V/Ag multilayers of different layer thickness as well as pure Ag and V. The radiation-induced hardening was found to decrease with decreasing individual layer thickness. No change in hardness after implantation was measured in multilayers with a layer thickness of less than 10 nm, which is of the order of the average spacing of He bubbles. The pure V films exhibit significant hardening due to a dense distribution of 0.8 nm diameter He bubbles, but in the nanocrystalline pure Ag films bubbles grow to a diameter of approximately 20 nm and become ineffective in causing hardening. A model describing layer-thickness-dependent radiation hardening in multilayers was developed by extending the Friedel model to take into account the layer thickness and the He bubble spacing. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.