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.
Bibliographical noteFunding Information:
This material is based upon work supported as part of the Center for Materials at Irradiation and Mechanical Extremes, an Energy Frontier Research Center funded by the US Department of Energy, Office of Basic Energy Sciences. The ion implantation and analysis work was supported by the LANL Laboratory Directed Research and Development (LDRD) program. This work was performed, in part, at the Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences user facility. 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. We thank J. Wang, X.Y. Liu, M.J. Demkowicz, R.G. Hoagland, and J.P. Hirth for insightful discussion.
- Transmission electron microscopy