Comparison of size dependent strengthening mechanisms in Ag/Fe and Ag/Ni multilayers

Nanostructured metallic multilayers have attracted substantial attention as they often possess high mechanical strength. Here we report on the microstructure and mechanical strength of sputtered Ag/Fe multilayers with individual layer thicknesses (h) varying from 1 to 200 nm. Phase transformation of Fe from body-centered-cubic (bcc) to face-centered-cubic (fcc) structure occurs when h < 5 nm. Nanotwins form in fine Ag/Fe multilayers. Although modulus mismatch is similar between Ag/Fe and Ag/Ni multilayers, the peak hardnesses of Ag/Fe multilayers is much lower than that of Ag/Ni system. Comparison of mechanical strength of several Ag based multilayers reveals that this drastic difference may arise from chemical stress due to the difference in stacking fault energy of the layer constituents. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.