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A critical examination of the paradox of strength and ductility in ultrafine-grained metals

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Abstract

The paradox of strength and ductility is now well established and denotes the difficulty of simultaneously achieving both high strength and high ductility. This paradox was critically examined using a cast Al–7%Si alloy processed by high-pressure torsion (HPT) for up to 10 turns at a temperature of either 298 or 445 K. This processing reduces the grain size to a minimum of ∼0.4 µm and also decreases the average size of the Si particles. The results show that samples processed to high numbers of HPT turns exhibit both high strength and high ductility when tested at relatively low strain rates and the strain rate sensitivity under these conditions is ∼0.14 which suggests that flow occurs by some limited grain boundary sliding and crystallographic slip. The results are also displayed on the traditional diagram for strength and ductility and they demonstrate the potential for achieving high strength and high ductility by increasing the number of turns in HPT.

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ACKNOWLEDGMENTS

The authors would like to acknowledge the help of Mr. Devi Lal and Mr. Amit Kumar in data analysis and microscopy of fractured surfaces, respectively, and they thank Dr. Sarath Menon of Naval Postgraduate School, Monterey, CA, USA, for providing the cast Al–7%Si samples. This work was partially funded by a Seed Grant (Indian Institute of Science, Bangalore) to PK. The work was supported in part by the National Science Foundation of the United States under Grant No. DMR-1160966 and in part by the European Research Council under ERC Grant Agreement No. 267464-SPDMETALS.

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Authors and Affiliations

  1. Department of Materials Engineering, Indian Institute of Science, Bangalore, 560012, India

    Tarang Mungole & Praveen Kumar

  2. Division of Materials Science and Engineering, Hanyang University, Seoul, 133-791, South Korea

    Megumi Kawasaki

  3. Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA, 90089-1453, USA

    Megumi Kawasaki & Terence G. Langdon

  4. Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, SO17 1BJ, UK

    Terence G. Langdon

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  1. Tarang Mungole
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Correspondence to Praveen Kumar.

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Mungole, T., Kumar, P., Kawasaki, M. et al. A critical examination of the paradox of strength and ductility in ultrafine-grained metals. Journal of Materials Research 29, 2534–2546 (2014). https://doi.org/10.1557/jmr.2014.272

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