《金属材料强韧化与组织调控》教学资源（参考文献）Extreme grain refinement by severe plastic deformation：A wealth of challenging science

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.2012.10.038

Extreme 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

Y.Estrin,A.Vinogradov/Acta Materialia 61 (2013)782-817 783 similar effect is well known in fatigue where the grain size the reviews [21,22]and special issues of Advanced Engineer- of wavy-slip materials has no bearing on the fatigue limit. ing Materials [23],Materials Science and Engineering A [24] These observations can be associated with the vital role and Materials Transactions [25,26]. of the dislocation substructure,which forms during defor- What makes SPD processing techniques so popular is mation(be it monotonic or cyclic),and it is the size of the the possibility of using them to enhance the strength char- substructure which determines the strength characteristics acteristics of conventional metallic materials in a quite of metallic materials.Gow and Cahn [9]emphasized the spectacular way:by a factor of up to eight for pure metals significance of crystallographic texture for the deformation such as copper and by some 30-50%for alloys [7,27]. and recrystallization behaviour of metals and the effect of Despite the impressive property improvement achievable evolving texture on the resultant properties.Bell and Cahn with SPD techniques,their uptake by industry has been [10]outlined many fine features of mechanical twinning, rather sluggish.However,things are now starting to which play an important part in plastic deformation when change,and there is a common feeling in the nanoSPD accommodation by dislocation slip is hindered.Beck [11] community that major breakthroughs in terms of indus- highlighted the possibility of relieving the work-hardening try-scale applications of SPD-based technologies are immi- effects by post-processing recovery.As will be seen in the nent.We have been working in this area for more than a following sections,these ideas have had a great impact decade and have followed its developments closely.In this on the development of the SPD processing and are pivotal article we present our views on what has been achieved, to the modern concepts underlying these techniques.Now- what is possibly achievable,and what future trends are to adays,the subject of SPD processing is represented very be expected from SPD processing technologies.This article prominently on the pages of Acta,as illustrated by the does not represent a full review of the SPD area (one could analysis in Ref.[4].Its revival is due to the work of Segal almost say the discipline of SPD,considering the firm place et al.[12]in the Soviet Union in the mid-1970s.These this group of material processing techniques has taken in authors developed the method of equal-channel angular literature).Rather,it is our personal take on the SPD area pressing (ECAP),which later evolved into what is now and an attempt to foretell its future development.Empha- the most popular SPD technique.It should be mentioned, sis is placed on the scientifically challenging aspects of however,that in the time between the publication of Bridg- SPD,and not so much on technological issues,although man's studies and the reintroduction of this subject in the some insights into the promises and limitations of SPD metal science literature,exploration of the possibilities of technologies will also be given. changing the properties of materials through combined high pressure and shear deformation went on both in the 2.SPD methods Soviet Union and in the West.This less known work has been reviewed in Ref.[13].In particular,credit should be Among the procedures devised for grain refinement. given to the work by the group of N.S.Enikolopian con- SPD techniques are of particular interest and are the ducted mainly on polymers. focus of the present review.These techniques enjoy great A real appreciation for the new possibilities for improv- popularity owing to their ability to produce considerable ing the properties of metallic materials provided by SPD grain refinement in fully dense.bulk-scale work-pieces. techniques came with the work of the group of Valiev thus giving promise for structural applications.The [14,15],which demonstrated the relation between the achievable grain sizes lie within the submicrometer(100- enhanced strength and the extreme grain refinement 1000 nm)and nanometer (<100 nm)ranges.SPD-pro- imparted by SPD processing to a range of metals and cessed materials with such grain sizes are generally alloys.The seminal work of this group,emphasizing the referred to as nanoSPD materials [7],although only the great potential of SPD processing with regard to property latter ones can be regarded as being nanostructured improvement through grain structure modification,has according to the conventional definition.Several compre- heralded what has been described as the "microstructural hensive reviews have focused on various nanoSPD pro- age"of SPD research [4].Over the last decade,the nano- cessing techniques [22,28-33].We refer the reader to the SPD community (www.nanospd.org)has grown to an original works for specific details and only briefly outline impressive group of researchers,and thousands of publica- the general SPD methodology underlining the common tions on ultrafine-grained (UFG)and nanostructured features and the most important differences between the materials produced by SPD have been published.It is nanoSPD processes.By no means do we claim that our probably not surprising that in the year of the Diamond list of currently available manufacturing schemes is Jubilee of this journal,the Acta Materialia Gold Medal exhaustive. goes to Professor Terry Langdon-one of the world leaders After the landmark work by Bridgman mentioned above in the area of nanoSPD materials.A representative collec- [6.341.Langford and Cohen [35]and Rack and Cohen [36] tion of the relevant articles on the subject can be found in demonstrated in the 1960s that the microstructure of Fe- the proceedings of symposia on UFG materials [16,18]and 0.003%C subjected to high strains by wire drawing was nanoSPD conferences [19,20]the most recent ones in a refined to subgrain sizes in the 200-500 nm range.These series of five such forums.Further useful sources include microstructures could not be regarded as UFG proper in

similar effect is well known in fatigue where the grain size of wavy-slip materials has no bearing on the fatigue limit. These observations can be associated with the vital role of the dislocation substructure, which forms during defor￾mation (be it monotonic or cyclic), and it is the size of the substructure which determines the strength characteristics of metallic materials. Gow and Cahn [9] emphasized the significance of crystallographic texture for the deformation and recrystallization behaviour of metals and the effect of evolving texture on the resultant properties. Bell and Cahn [10] outlined many fine features of mechanical twinning, which play an important part in plastic deformation when accommodation by dislocation slip is hindered. Beck [11] highlighted the possibility of relieving the work-hardening effects by post-processing recovery. As will be seen in the following sections, these ideas have had a great impact on the development of the SPD processing and are pivotal to the modern concepts underlying these techniques. Now￾adays, the subject of SPD processing is represented very prominently on the pages of Acta, as illustrated by the analysis in Ref. [4]. Its revival is due to the work of Segal et al. [12] in the Soviet Union in the mid-1970s. These authors developed the method of equal-channel angular pressing (ECAP), which later evolved into what is now the most popular SPD technique. It should be mentioned, however, that in the time between the publication of Bridg￾man’s studies and the reintroduction of this subject in the metal science literature, exploration of the possibilities of changing the properties of materials through combined high pressure and shear deformation went on both in the Soviet Union and in the West. This less known work has been reviewed in Ref. [13]. In particular, credit should be given to the work by the group of N.S. Enikolopian con￾ducted mainly on polymers. A real appreciation for the new possibilities for improv￾ing the properties of metallic materials provided by SPD techniques came with the work of the group of Valiev [14,15], which demonstrated the relation between the enhanced strength and the extreme grain refinement imparted by SPD processing to a range of metals and alloys. The seminal work of this group, emphasizing the great potential of SPD processing with regard to property improvement through grain structure modification, has heralded what has been described as the “microstructural age” of SPD research [4]. Over the last decade, the nano￾SPD community (www.nanospd.org) has grown to an impressive group of researchers, and thousands of publica￾tions on ultrafine-grained (UFG) and nanostructured materials produced by SPD have been published. It is probably not surprising that in the year of the Diamond Jubilee of this journal, the Acta Materialia Gold Medal goes to Professor Terry Langdon—one of the world leaders in the area of nanoSPD materials. A representative collec￾tion of the relevant articles on the subject can be found in the proceedings of symposia on UFG materials [16,18] and nanoSPD conferences [19,20]—the most recent ones in a series of five such forums. Further useful sources include the reviews [21,22] and special issues of Advanced Engineer￾ing Materials [23], Materials Science and Engineering A [24] and Materials Transactions [25,26]. What makes SPD processing techniques so popular is the possibility of using them to enhance the strength char￾acteristics of conventional metallic materials in a quite spectacular way: by a factor of up to eight for pure metals such as copper and by some 30–50% for alloys [7,27]. Despite the impressive property improvement achievable with SPD techniques, their uptake by industry has been rather sluggish. However, things are now starting to change, and there is a common feeling in the nanoSPD community that major breakthroughs in terms of indus￾try-scale applications of SPD-based technologies are immi￾nent. We have been working in this area for more than a decade and have followed its developments closely. In this article we present our views on what has been achieved, what is possibly achievable, and what future trends are to be expected from SPD processing technologies. This article does not represent a full review of the SPD area (one could almost say the discipline of SPD, considering the firm place this group of material processing techniques has taken in literature). Rather, it is our personal take on the SPD area and an attempt to foretell its future development. Empha￾sis is placed on the scientifically challenging aspects of SPD, and not so much on technological issues, although some insights into the promises and limitations of SPD technologies will also be given. 2. SPD methods Among the procedures devised for grain refinement, SPD techniques are of particular interest and are the focus of the present review. These techniques enjoy great popularity owing to their ability to produce considerable grain refinement in fully dense, bulk-scale work-pieces, thus giving promise for structural applications. The achievable grain sizes lie within the submicrometer (100– 1000 nm) and nanometer (<100 nm) ranges. SPD-pro￾cessed materials with such grain sizes are generally referred to as nanoSPD materials [7], although only the latter ones can be regarded as being nanostructured according to the conventional definition. Several compre￾hensive reviews have focused on various nanoSPD pro￾cessing techniques [22,28–33]. We refer the reader to the original works for specific details and only briefly outline the general SPD methodology underlining the common features and the most important differences between the nanoSPD processes. By no means do we claim that our list of currently available manufacturing schemes is exhaustive. After the landmark work by Bridgman mentioned above [6,34], Langford and Cohen [35] and Rack and Cohen [36] demonstrated in the 1960s that the microstructure of Fe– 0.003% C subjected to high strains by wire drawing was refined to subgrain sizes in the 200–500 nm range. These microstructures could not be regarded as UFG proper in Y. Estrin, A. Vinogradov / Acta Materialia 61 (2013) 782–817 783

784 Y.Estrin,A.Vinogradov/Acta Materialia 61 (2013)782-817 Table 1 Schematic illustration of some basic and modern SPD techniques. Process Schematic illustration Equivalent strain Ref. Basic processes (a)Equal-channel angular pressing ef=N头cot(p) [39 (ECAP) N,the number of ECAP passes m⊙ → (b)High-pressure torsion (HPT) ei=N头g 34 r.the distance from the axis,t,the thickness of the sample,N,the number of revolutions (c)Accumulative roll bonding (ARB) e=N孟ln(》) [54 to.the initial thickness of the sample..the thickness of the sample after rolling,N.the number of passes (d)Multi-axial forging ew=N孟ln(g [57 Strain is non-uniform.N,the number of processing steps (e)Twist extrusion (TE) ≈0.4+0.1iar:时≈N1amm [61] y is the twist line slope:N is the number of passes. Deformation is non-uniform Dericative processes (f)Repetitive side extrusion ECAP equivalent [65] (continued on next page)

Table 1 Schematic illustration of some basic and modern SPD techniques. Process Schematic illustration Equivalent strain Ref. Basic processes (a) Equal-channel angular pressing (ECAP) eeff ¼ N 2ffiffi 3 p cotð/Þ N, the number of ECAP passes [39] (b)High-pressure torsion (HPT) eeff ¼ N 2ffiffi 3 p pr t r, the distance from the axis, t, the thickness of the sample, N, the number of revolutions [34] (c) Accumulative roll bonding (ARB) eeff ¼ N 2ffiffi 3 p lnð t0 tÞ t0, the initial thickness of the sample, t, the thickness of the sample after rolling, N, the number of passes [54] (d) Multi-axial forging eeff ¼ N 2ffiffi 3 p lnða bÞ Strain is non-uniform. N, the number of processing steps [57] (e) Twist extrusion (TE) emin eff 0:4 þ 0:1tanc; emax eff N 2ffiffi 3 p tanc c is the twist line slope; N is the number of passes. Deformation is non-uniform [61] Derivative processes (f) Repetitive side extrusion ECAP equivalent [65] (continued on next page) 784 Y. Estrin, A. Vinogradov / Acta Materialia 61 (2013) 782–817

Y.Estrin,A.Vinogradov/Acta Materialia 61 (2013)782-817 785 Table 1 (continued) Process Schematic illustration Equivalent strain Ref. (g)Rotary-die ECAP ECAP equivalent [66 (h)Cyclic extrusion-compression terr N4In() [75] (CEC) N,number of cycles (i)Cyclic close-die forging (CCDF) teff =Nn(#) [76) N,number of cycles (k)Repetitive corrugation and teff =Nn(ts) [72] straightening(RCS) N.number of cycles Integrated processes (1)Integrated extrusion+ECAP [110,11 (m)Parallel channel ECAP (PC. ECAP equivalent [67] ECAP) Continuous processes (n)ECAP-Conform [37][120]

Table 1 (continued) Process Schematic illustration Equivalent strain Ref. (g) Rotary-die ECAP ECAP equivalent [66] (h) Cyclic extrusion–compression (CEC) eeff ¼ N4 lnðD d Þ N, number of cycles [75] (i) Cyclic close-die forging (CCDF) eeff ¼ N 2ffiffi 3 p lnðH W Þ N, number of cycles [76] (k) Repetitive corrugation and straightening (RCS) eeff ¼ N 4ffiffi 3 p lnð rþt rþ0:5t Þ N, number of cycles [72] Integrated processes (l) Integrated extrusion + ECAP [110,111] (m) Parallel channel ECAP (PC￾ECAP) ECAP equivalent [67] Continuous processes (n) ECAP- Conform [37] [120] Y. Estrin, A. Vinogradov / Acta Materialia 61 (2013) 782–817 785

786 Y.Estrin.A.Vinogradov/Acta Materialia 61 (2013)782-817 Table 1 (continued) Process Schematic illustration Equivalent strain Ref. (o)Con-shearing [121] (p)Continuous confined strip [122] shearing (C2S2) (q)Continuous repetitive corrugating [73) and straightening (RCS) (r)Incremental ECAP(I-ECAP) [126 (s)Continuous high-pressure torsion [127] (t)Continuous manufacturing [129] of bolts the sense of the commonly accepted definitions [7],because between nanoSPD materials and more conventional mate- most of the sub-boundaries were low angle.Indeed,it is the rials with subgrain structures produced by cold rolling or prevalence of high-angle grain boundaries that is com- other common metal forming techniques.This distinction monly believed to be a signature of UFG materials manu- notwithstanding,these works opened the gates for micro- factured by SPD.This constitutes a clear demarcation line structure refinement by deformation to gigantic strains

the sense of the commonly accepted definitions [7], because most of the sub-boundaries were low angle. Indeed, it is the prevalence of high-angle grain boundaries that is com￾monly believed to be a signature of UFG materials manu￾factured by SPD. This constitutes a clear demarcation line between nanoSPD materials and more conventional mate￾rials with subgrain structures produced by cold rolling or other common metal forming techniques. This distinction notwithstanding, these works opened the gates for micro￾structure refinement by deformation to gigantic strains. Table 1 (continued) Process Schematic illustration Equivalent strain Ref. (o) Con-shearing [121] (p) Continuous confined strip shearing (C2S2) [122] (q) Continuous repetitive corrugating and straightening (RCS) [73] (r) Incremental ECAP (I-ECAP) [126] (s) Continuous high-pressure torsion [127] (t) Continuous manufacturing of bolts [129] 786 Y. Estrin, A. Vinogradov / Acta Materialia 61 (2013) 782–817