Tensile behavior of fully nanotwinned alloys with varying stacking fault energies

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Research Letter

Tensile behavior of fully nanotwinned alloys with varying stacking fault energies Nathan M. Heckman, Department of Aerospace and Mechanical Engineering, Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, CA 900089, USA Leonardo Velasco, Department of Aerospace and Mechanical Engineering, Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, CA 900089, USA; Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology, Hermann-vonHelmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany Andrea M. Hodge, Department of Aerospace and Mechanical Engineering, Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, CA 900089, USA Address all Correspondence to Andrea M. Hodge at [email protected] (Received 16 December 2016; accepted 28 April 2017)

Abstract In this study, a comparison of the tensile behavior of fully nanotwinned Cu–6 wt.%Al, Cu–2 wt.%Al, and Cu–10 wt.%Ni with stacking fault energies (SFEs) of 6, 37, and 60 mJ/m2, respectively is presented. The samples displayed yield strengths ranging from 830 to 1340 MPa, varying with both alloy content and microstructural parameters. All samples showed low ductility, even though there are tilted twin boundaries present in Cu–10 wt.%Ni. The influence of varying grain width is presented for each alloy and related to both the activation volume and SFE [Figs. 3(a)–3(c)].

There has been much interest in nanotwinned (NT) metals, largely due to the potential for simultaneous strength and ductility, corrosion resistance, and thermal stability in comparison with nanocrystalline metals.[1–5] Owing to these properties, efforts have been made to introduce nanotwins into common engineering alloys such as various steels and brass.[6–9] However, those studies only produced partially NT samples and therefore the impact of the alloy content cannot be isolated. Thus, in order to further advance and effectively utilize NT structures in alloys, it is important to first understand the behavior of fully NT systems of various compositions. The mechanical behavior of fully NT metals has been investigated primarily in single-element NT Cu focusing on how microstructural parameters such as twin thickness and grain size influence the properties.[10–13] It has been shown in equiaxed NT Cu that decreasing twin thickness leads to higher strength and ductility down to a ‘critical twin thickness’, typically of the order of nanometers, below which the ductility continues to increase but strength decreases.[10] Simulations on equiaxed NT Cu indicate that this ‘critical twin thickness’ decreases as grain size is reduced, and so it is possible to achieve higher strengths at smaller grain sizes.[12,13] There is also a potential loss of ductility with decreasing grain size, as indicated in some experimental results.[11] In the case of alloys, due to the lack of fully NT samples, mechanical results are s

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