Available online at www.sciencedirect.com SciVerse ScienceDirect Cta MATERIALIA ELSEVIER Acta Materialia 61 (2013)782-817 www.elsevier.com/locate/actamat Extreme grain refinement by severe plastic deformation:A wealth of challenging science Y.Estrin4,A.Vinogradovb.I Centre for Advanced Hybrid Materials,Department of Materials Engineering.Monash University.Clayton,VIC3800.Australia Laboratory for the Physics of Strength of Materials and Intelligent Diagnostic Systems.Togliatti State University.Togliatti 445667.Russia Abstract This article presents our take on the area of bulk ultrafine-grained materials produced by severe plastic deformation(SPD).Over the last decades,research activities in this area have grown enormously and have produced interesting results,which we summarise in this concise review.This paper is intended as an introduction to the field for the "uninitiated",while at the same time highlighting some polemic issues that may be of interest to those specialising in bulk nanomaterials produced by SPD.A brief overview of the available SPD technologies is given,along with a summary of unusual mechanical,physical and other properties achievable by SPD processing. The challenges this research is facing-some of them generic and some specific to the nanoSPD area-are identified and discussed. 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved. Keywords:Severe plastic deformation;Ultrafine-grained materials;Modelling;Properties 1.Historical overview developed the scientific grounds and techniques for materi- als processing through a combination of high hydrostatic Grain size can be regarded as a key microstructural fac- pressure and shear deformation [5,6],which today are at tor affecting nearly all aspects of the physical and mechan- the core of SPD methods.Bridgman effectively introduced ical behaviour of polycrystalline metals as well as their the defining characteristics of SPD processing in the early chemical and biochemical response to the surrounding 1950s.In a strict sense generally accepted in the materials media.Hence,control over grain size has long been recog- engineering community,an SPD process is currently nized as a way to design materials with desired properties. defined as"any method of metal forming under an exten- Most of the mentioned properties benefit greatly from sive hydrostatic pressure that may be used to impose a very grain size reduction.As the race for better materials perfor- high strain on a bulk solid without the introduction of any mance is never ending,attempts to develop viable tech- significant change in the overall dimensions of the sample niques for microstructure refinement continue.A possible and having the ability to produce exceptional grain refine- avenue for microstructure refinement of metals is the use ment"[7].In this Diamond Jubilee issue of Acta Materialia of severe plastic deformation (SPD)a principle that is it is appropriate to mention that many of the modern ideas as old as metalworking itself.Recent essays [1-4]tell a fas- of thermomechanical processing involved in virtually all cinating story of the art of ancient swordmaking through SPD schemes were already addressed in the first volume SPD.The modern-day history of SPD technology has its of Acta Metallurgica in 1953.Carreker and Hibbard [8] beginnings in the seminal work by P.W.Bridgman who pointed out that the yield strength of high-purity copper benefits substantially from grain refinement and this effect Corresponding author.Tel:+61 420822164. is more pronounced at low temperatures.They also noticed E-mail address:yuri.estrin@monash.edu (Y.Estrin). that the effect of the initial grain size vanishes at strains lar- On leave from the Department of Intelligent Materials Engineering. ger than 0.1 and for that reason the grain size has little or Osaka City University,Osaka 558-8585,Japan. no influence on the strength under monotonic loading.A 1359-6454/S36.00 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved. http://dx.doi.org/10.1016/j.actamat.2012.10.038Extreme grain refinement by severe plastic deformation: A wealth of challenging science Y. Estrin a,⇑ , A. Vinogradov b,1 a Centre for Advanced Hybrid Materials, Department of Materials Engineering, Monash University, Clayton, VIC 3800, Australia bLaboratory for the Physics of Strength of Materials and Intelligent Diagnostic Systems, Togliatti State University, Togliatti 445667, Russia Abstract This article presents our take on the area of bulk ultrafine-grained materials produced by severe plastic deformation (SPD). Over the last decades, research activities in this area have grown enormously and have produced interesting results, which we summarise in this concise review. This paper is intended as an introduction to the field for the “uninitiated”, while at the same time highlighting some polemic issues that may be of interest to those specialising in bulk nanomaterials produced by SPD. A brief overview of the available SPD technologies is given, along with a summary of unusual mechanical, physical and other properties achievable by SPD processing. The challenges this research is facing—some of them generic and some specific to the nanoSPD area—are identified and discussed. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Severe plastic deformation; Ultrafine-grained materials; Modelling; Properties 1. Historical overview Grain size can be regarded as a key microstructural fac￾tor affecting nearly all aspects of the physical and mechan￾ical behaviour of polycrystalline metals as well as their chemical and biochemical response to the surrounding media. Hence, control over grain size has long been recog￾nized as a way to design materials with desired properties. Most of the mentioned properties benefit greatly from grain size reduction. As the race for better materials perfor￾mance is never ending, attempts to develop viable tech￾niques for microstructure refinement continue. A possible avenue for microstructure refinement of metals is the use of severe plastic deformation (SPD)—a principle that is as old as metalworking itself. Recent essays [1–4] tell a fas￾cinating story of the art of ancient swordmaking through SPD. The modern-day history of SPD technology has its beginnings in the seminal work by P.W. Bridgman who developed the scientific grounds and techniques for materi￾als processing through a combination of high hydrostatic pressure and shear deformation [5,6], which today are at the core of SPD methods. Bridgman effectively introduced the defining characteristics of SPD processing in the early 1950s. In a strict sense generally accepted in the materials engineering community, an SPD process is currently defined as “any method of metal forming under an exten￾sive hydrostatic pressure that may be used to impose a very high strain on a bulk solid without the introduction of any significant change in the overall dimensions of the sample and having the ability to produce exceptional grain refine￾ment” [7]. In this Diamond Jubilee issue of Acta Materialia it is appropriate to mention that many of the modern ideas of thermomechanical processing involved in virtually all SPD schemes were already addressed in the first volume of Acta Metallurgica in 1953. Carreker and Hibbard [8] pointed out that the yield strength of high-purity copper benefits substantially from grain refinement and this effect is more pronounced at low temperatures. They also noticed that the effect of the initial grain size vanishes at strains lar￾ger than 0.1 and for that reason the grain size has little or no influence on the strength under monotonic loading. A 1359-6454/$36.00 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actamat.2012.10.038 ⇑ Corresponding author. Tel.: +61 420822164. E-mail address: yuri.estrin@monash.edu (Y. Estrin). 1 On leave from the Department of Intelligent Materials Engineering, Osaka City University, Osaka 558–8585, Japan. www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 61 (2013) 782–817