In complex loading conditions (e.g., sliding contact), mechanical properties, such as strain hardening and initial hardness, will dictate the long-term performance of materials systems. With this in mind, the strain hardening behaviors of Cu/Nb nanoscale metallic multilayer systems were examined by performing nanoindentation tests within nanoscratch wear boxes and undeformed regions (as-deposited). Both the architecture and substrate influence were examined by utilizing three different individual layer thicknesses (2, 20, and 100 nm) and two total film thicknesses (1 and 10 µm). After nano-wear deformation, multilayer systems with thinner layers showed less volume loss as measured by laser scanning microscopy. Additionally, the hardness of the deformed regions significantly rose with respect to the as-deposited measurements, which further increased with greater wear loads. Strain hardening exponents for multilayers with thinner layers (2 and 20 nm, n ≈ 0.018 and n ≈ 0.022, respectively) were less than that determined for 100 nm systems (n ≈ 0.041). These results suggest that single-dislocation-based deformation mechanisms observed for the thinner systems limit the extent of achievable strain hardening. This conclusion indicates that impacts of both architecture strengthening and strain hardening must be considered to accurately predict multilayer performance during sliding contact across varying length scales.
|Original language||English (US)|
|Number of pages||13|
|Journal||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|State||Published - Mar 1 2016|
Bibliographical noteFunding Information:
This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. 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 U.S. Department of Energy under contract DE-AC52-06NA25396. Electron microscopy was conducted as part of a user proposal at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. The authors wish to thank the assistance of Dr. M.J. Cordill (Erich Schmidt Institute of Materials Science), Dr. J.E. Harriss (Clemson University), Dr. L.V. Saraf (Clemson University), Dr. J.L. Sharp (Clemson University), and Mr. L. Kuhn (Hysitron Co.) for their helpful discussions and guidance. The authors also wish to thank Mr. J.K. Baldwin for his efforts in film deposition and Ms. D.W. Coffey for her efforts in FIB-S/TEM specimen preparation. In addition, the authors thank Mr. G. Kimball at Clemson University for editorial assistance.
© 2016, The Minerals, Metals & Materials Society and ASM International.