Mechanical properties and strengthening mechanism of Ni/Al nanolaminates: Role of dislocation strengthening and constraint in soft layers

This work focuses on the mechanical properties and strengthening mechanism of Ni/Al nanolaminates, where dislocation strengthening and constraint dominate in the soft Al nanolayers. Nanoindentation and micropillar compression experiments highlight a constrained plasticity of Al nanolayers, which endows Ni/Al nanolaminates with a strain hardened behavior. Plasticity of Ni/Al nanolaminate begins with yielding of Al, and the Al yield strength depends on the individual layer thickness. Based on an inverse methodology, the Al yield strength as a function of Al grain size is determined. The results evi-dence a significant strengthening in the Al nanolayers. Specially, when Al layer thickness decreases from X110 nm to X16 nm, its yield strength is increased for X68 %, from X0.69 GPa to X1.16 GPa. The strength-ening rule follows a confined layer slip model that is developed based on confining of single dislocation loops in nanolayers. Both the dislocation strengthening and the constraint effects in the Al layers con-tribute to a more sensitivity of Ni/Al strength with the variation of Al layer thickness, instead of Ni layer thickness. The work may forward the fundamental understanding in the strengthening mechanism and mechanical behavior of metallic nanolaminates with large elastoplastic mismatch.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study focuses on the mechanical properties and strengthening mechanism of Ni/Al nanolaminates, which are dominated by dislocation strengthening and constraint effects in the soft Al nanolayers. Nanoindentation and micropillar compression experiments reveal a constrained plasticity of Al nanolayers, resulting in a strain hardened behavior of Ni/Al nanolaminates. The strength of Al nanolayers is significantly increased with decreasing Al layer thickness, while the Ni layer thickness has less effect on the strength variation. The findings provide valuable insights into the strengthening mechanism and mechanical behavior of metallic nanolaminates with large elastoplastic mismatch.