Sputter-deposited epitaxial (111) and (110) Ag films have high-density nanotwins with respective twin boundary orientations perpendicular and angled to the growth direction. Twin density in as-deposited (111) Ag films is much greater than in (110) films, leading to higher hardness in the (111) films. Annealing up to 800 °C (homologous temperature of 0.85 Tm) leads to increased twin thickness, although the average twin thickness remains < 100 nm in both systems. Twinned volume fraction falls dramatically in annealed (110) films but remains constant at ~50% in (111) films. The mechanisms leading to the elimination of nanotwins in (110) films and their remarkable stability in (111) films at elevated temperatures are discussed. Coarsening and elimination of twins result in hardness reduction after annealing. The variety of microstructures achieved via annealing allows for the introduction of a strengthening model considering both twin and grain boundaries.
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We acknowledge financial support by NSF-DMR metallic materials and nanostructures program under grant no 0644835. Access to the microscopes at the Microscopy and Imaging Center at Texas A&M University is also acknowledged.
This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr-editor-manuscripts/.
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Bufford, D., Wang, H. & Zhang, X. Thermal stability of twins and strengthening mechanisms in differently oriented epitaxial nanotwinned Ag films. Journal of Materials Research 28, 1729–1739 (2013). https://doi.org/10.1557/jmr.2013.50