Surface flaws control strain localization in the deformation of CuAu nanolaminate pillars
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Research Letter
Surface flaws control strain localization in the deformation of Cu|Au nanolaminate pillars Adrien Gola, Department of Microsystems Engineering, University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg, Germany; Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), Straße am Forum 4, 76131 Karlsruhe, Germany Guang-Ping Zhang , Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, P.R. China Lars Pastewka , Department of Microsystems Engineering, University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg, Germany; Freiburg Materials Research Center, University of Freiburg, 79104 Freiburg, Germany Ruth Schwaiger , Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 EggensteinLeopoldshafen, Germany Address all correspondence to Lars Pastewka at [email protected] (Received 5 June 2019; accepted 28 June 2019)
Abstract The authors carried out matched experiments and molecular dynamics simulations of the compression of nanopillars prepared from Cu|Au nanolaminates with up to 25 nm layer thickness. The stress–strain behaviors obtained from both techniques are in excellent agreement. Variation in the layer thickness reveals an increase in the strength with a decreasing layer thickness. Pillars fail through the formation of shear bands whose nucleation they trace back to the existence of surface flaws. This combined approach demonstrates the crucial role of contact geometry in controlling the deformation mode and suggests that modulus-matched nanolaminates should be able to suppress strain localization while maintaining controllable strength.
Mechanical properties of materials deviate from bulk behavior when characteristic dimensions become small. Such deviations may occur when either microstructural features, e.g., the grain size, or object dimensions approach the length scale of the process that controls the deformation. As a result, the mechanical strength of micro- or nanoscale pure metallic materials has been found to be an order of magnitude higher than of their bulk counterparts.[1–3] A special class of nanostructured materials are metallic nanolaminates with nanoscale layers of two different materials. They not only exhibit enhanced strength and hardness,[4–8] wear resistance,[9,10] or toughness,[11] but also offer the possibility to tailor those properties by choosing material combinations.[12] Nanolaminates exhibit a range of different deformation behaviors, which depend on the combination of materials, the type of interfaces,[13] and the thickness of the laminate layers.[8] Reducing the thickness λ of the layer increases the flow strength σ of the material, with Hall–Petch-like behavior, σ ∝ λ −1/2 at large thickness transitioning to the confined layer slip σ ∝ ln(λ)/λ at smaller thickness. Shear band instabilities were observed for several crystalline systems and attributed to a reduced strain hardening
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