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

Published online by Cambridge University Press:  07 October 2014

Tarang Mungole ,
Praveen Kumar ,
Megumi Kawasaki  and
Terence G. Langdon
Tarang Mungole
Affiliation:
Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India
Praveen Kumar*
Affiliation:
Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India
Megumi Kawasaki
Affiliation:
Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, South Korea; and Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA
Terence G. Langdon
Affiliation:
Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA; and Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK
*
a)Address all correspondence to this author. e-mail: praveenk@materials.iisc.ernet.in
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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.

Keywords

Al–Si alloyductilityhigh-pressure torsionstrengthultrafine grains
Type
Articles
Information
Journal of Materials Research , Volume 29 , Issue 21 , 14 November 2014 , pp. 2534 - 2546
Copyright
Copyright © Materials Research Society 2014 

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References

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