Act MATERIALIA Pergamon Acta mater.49(2001)1497-1505 www.elsevier.com/locate/actamat MICROSTRUCTURES AND DISLOCATION CONFIGURATIONS IN NANOSTRUCTURED Cu PROCESSED BY REPETITIVE CORRUGATION AND STRAIGHTENING J.Y.HUANGi,Y.T.ZHU,H.JIANG and T.C.LOWE Materials Science and Technology Division,MS G 755,Los Alamos National Laboratory,Los Alamos, NM 87545.USA Received 6 November 2000:accepted 5 February 2001 Abstract-The microstructures and dislocation configurations in nanostructured Cu processed by a new tech- nique,repetitive corrugation and straightening (RCS),were studied using transmission electron microcopy (TEM)and high resolution TEM.Most dislocations belong to 60 type and tend to pile up along the (111] slip planes.Microstructural features including low-angle grain boundaries(GBs),high-angle GBs,and equilib- rium and non-equilibrium GBs and subgrain boundaries were observed.Dislocation structures at an intermedi- ate deformation strain were studied to investigate the microstructural evolutions,which revealed some unique microstructural features such as isolated dislocation cell (IDC),dislocation tangle zones (DTZs),and uncon- densed dislocation walls (UDWs).2001 Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved. Keywords:Repetitive corrugation straightening;Microstructure;Transmission electron microscopy (TEM): Copper 1.INTRODUCTION has been paid to alternative procedures of introducing ultrafine grains in materials by severe plastic defor- Many methods have been used to synthesize materials mation (SPD)[9-121. with ultrafine grain sizes (10-1000 nm),including inert gas condensation [1],high-energy ball milling One of the SPD variants,equal-channel angular pressing (ECAP),has been used to refine bulk, [2],sliding wear [3],etc.These techniques are attract- ive for producing powders with grain sizes below coarse-grained metals and alloys to grain sizes rang- 100 nm,but cannot be used to make bulk samples. ing from <0.I to I um [9-12].However,ECAP is To consolidate the nanometer-sized powders into bulk difficult to scale up to process volumes of materials materials,high pressure and moderate temperature are much larger than the 20x20x100 mm3 samples that usually needed.Grains might grow during consoli- are typically produced today.Furthermore,current dation,making the bulk materials partially or com- implementations of ECAP are discontinuous,requir- pletely lose the nanocharacteristics.It is usually ing labor intensive handling of the work-piece impossible to completely eliminate porosity,even in between process steps.These difficulties in fabricat- materials consolidated under very high pressure and ing bulk,nanostructured materials have been substan- temperature.In addition,nanopowders are very sus- tial road-blocks to the structural applications of nano- ceptible to oxidation and absorb large quantities of structured materials.Other SPD techniques that have impurities such as O2.H2 and N2,making it difficult been reported in the literature include multipass-coin- to obtain clean bulk materials.The porosity as well forge (MCF)[13]and multi-axis deformation [14]. as impurities significantly affect the mechanical Both of them have certain advantages over the ECAP properties of the bulk materials,often making them process.However,they also employ batch processing, brittle [4-8].These problems prevent us from study- which is not efficient for large-scale production. ing the intrinsic properties of bulk nanomaterials.As Recently,we have developed a new technique, a consequence of these difficulties,much attention repetitive corrugation and straightening (RCS),that can not only create bulk nanostructured materials free of contamination and porosity,but can also be easily To whom all correspondence should be addressed.Tel.: adapted to large-scale industrial production [15].In +1-505-665-0835:fax:+1-505-667-2264. the RCS process,a work-piece is repetitively bent and E-mail address:jyhuang@lanl.gov (J.Huang) straightened without significantly changing the cross- 1359-6454/01/$20.00 2001 Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved. P:S1359-6454(01)00069-6Acta mater. 49 (2001) 1497–1505 www.elsevier.com/locate/actamat MICROSTRUCTURES AND DISLOCATION CONFIGURATIONS IN NANOSTRUCTURED Cu PROCESSED BY REPETITIVE CORRUGATION AND STRAIGHTENING J. Y. HUANG†, Y. T. ZHU, H. JIANG and T. C. LOWE Materials Science and Technology Division, MS G 755, Los Alamos National Laboratory, Los Alamos, NM 87545, USA ( Received 6 November 2000; accepted 5 February 2001 ) Abstract—The microstructures and dislocation configurations in nanostructured Cu processed by a new tech￾nique, repetitive corrugation and straightening (RCS), were studied using transmission electron microcopy (TEM) and high resolution TEM. Most dislocations belong to 60° type and tend to pile up along the {111} slip planes. Microstructural features including low-angle grain boundaries (GBs), high-angle GBs, and equilib￾rium and non-equilibrium GBs and subgrain boundaries were observed. Dislocation structures at an intermedi￾ate deformation strain were studied to investigate the microstructural evolutions, which revealed some unique microstructural features such as isolated dislocation cell (IDC), dislocation tangle zones (DTZs), and uncon￾densed dislocation walls (UDWs).  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. Keywords: Repetitive corrugation straightening; Microstructure; Transmission electron microscopy (TEM); Copper 1. INTRODUCTION Many methods have been used to synthesize materials with ultrafine grain sizes (10–1000 nm), including inert gas condensation [1], high-energy ball milling [2], sliding wear [3], etc. These techniques are attract￾ive for producing powders with grain sizes below 100 nm, but cannot be used to make bulk samples. To consolidate the nanometer-sized powders into bulk materials, high pressure and moderate temperature are usually needed. Grains might grow during consoli￾dation, making the bulk materials partially or com￾pletely lose the nanocharacteristics. It is usually impossible to completely eliminate porosity, even in materials consolidated under very high pressure and temperature. In addition, nanopowders are very sus￾ceptible to oxidation and absorb large quantities of impurities such as O2, H2 and N2, making it difficult to obtain clean bulk materials. The porosity as well as impurities significantly affect the mechanical properties of the bulk materials, often making them brittle [4–8]. These problems prevent us from study￾ing the intrinsic properties of bulk nanomaterials. As a consequence of these difficulties, much attention † To whom all correspondence should be addressed. Tel.: +1-505-665-0835; fax: +1-505-667-2264. E-mail address: jyhuang@lanl.gov (J. Huang) 1359-6454/01/$20.00  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S13 59-6454(01)00069-6 has been paid to alternative procedures of introducing ultrafine grains in materials by severe plastic defor￾mation (SPD) [9–12]. One of the SPD variants, equal-channel angular pressing (ECAP), has been used to refine bulk, coarse-grained metals and alloys to grain sizes rang￾ing from
0.1 to 1 µm [9–12]. However, ECAP is difficult to scale up to process volumes of materials much larger than the 20×20×100 mm3 samples that are typically produced today. Furthermore, current implementations of ECAP are discontinuous, requir￾ing labor intensive handling of the work-piece between process steps. These difficulties in fabricat￾ing bulk, nanostructured materials have been substan￾tial road-blocks to the structural applications of nano￾structured materials. Other SPD techniques that have been reported in the literature include multipass-coin￾forge (MCF) [13] and multi-axis deformation [14]. Both of them have certain advantages over the ECAP process. However, they also employ batch processing, which is not efficient for large-scale production. Recently, we have developed a new technique, repetitive corrugation and straightening (RCS), that can not only create bulk nanostructured materials free of contamination and porosity, but can also be easily adapted to large-scale industrial production [15]. In the RCS process, a work-piece is repetitively bent and straightened without significantly changing the cross-