© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim pss current topics in solid state physics c status solidi www.pss-c.com physica Phys. Status Solidi C 7, No. 5, 1351– 1354 (2010) / DOI 10.1002/pssc.200983392 Structure and properties of copper after large strain deformation Kinga Rodak *,1 , Rafal M. Molak 2 , and Zbigniew Pakiela 2 1 Department of Materials Science, Silesian University of Technology, Krasinskiego 8, 40-019 Katowice, Poland 2 Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland Received 2 October 2009, revised 9 December 2009, accepted 14 December 2009 Published online 15 April 2010 Keywords Cu, structure, mechanical properties, deformation, plasticity * Corresponding author: e-mail Kinga.Rodak@polsl.pl, Phone: +48 33 603 44 08, Fax: +48 32 603 44 00, http://knom.polsl.pl © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction The consequence of severe plastic de- formation (SPD) is the crystal fragmentation of the mate- rial to an ultrafine or even nanograined dimension with large misorientation between grains. The changes in a spe- cific defect structure are responsible for unusual physical and mechanical properties of ultrafine-grained (UFG) ma- terials, which are very often controlled by relaxation proc- esses as dynamic recrystallization for example, that ac- company the SPD processes of Cu. In many experiments such as [1,2], have showed that in copper, discontinuous (or migration) dynamic recrystallization has occurred after large plastic strain at low temperatures as a results of lower stacking fault energy (SFE) and lower homologous tem- perature. Consequently, as mentioned in [3], the size of the structure elements and the mechanical properties change upon deformation nonmonotonously. Degtyrev and co- workers [4] showed that structure formation in Cu will be controlled by the temperature and the rate of deformation rather than the true strain. The microstructure in copper formed by severe plastic deformation is of special interest by reason of relaxation processes, which have rarely been taken into consideration in study mechanisms of grain re- finement. The present work was aimed to obtain a better understand- ing of the flow behavior and the evolution of microstruc- ture in copper during plastic deformation imposed by multi-axis compression methods. The multi-axis compres- sion is know in literature technique to impose cyclic com- pression in two orthogonal direction [5,6]. The knowledge of characteristic features of multi-axis compression materi- als will prove the usefulness of the employed method to produce materials having the desirable functional proper- ties. The evolution of misorientation distribution and crys- tallite size of the deformed samples were observed by us- ing the electron back scattered diffraction (EBSD) tech- nique, which is the only possible tool for analysis of rela- tively large areas [7]. 2 Experiment Investigations have been performed by use multi-axial compression techniques for refining Cu structure. Average strain in a single pass was 0.2, and 1-32 passes were applied. For samples deformed at 14.9, the av- erage strain in a single pass was 0.5 and 32 passes were applied. The samples were deformed with strain rate 0.5 s -1 . One can find more information about multi-axial compres- sion techniques in [5,6]. Commercial Cu (M1E) was used Structure and properties of Cu in dependence on strain (from ε~ 0.9 to ε~ 15) during multi-axial compression processing at room temperature was investigated. The evolution of disloca- tion structure, misorientation distribution and crystallite size were observed by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipment with electron back scattered diffraction (EBSD) facility. The mechanical properties of yield strength (YS), ultimate tensile strength (UTS) and uniform elongation was performed on MTS QTest/10 machine equipped with digital image correla- tion method (DIC). The structure–flow stress relationship of multi-axial compres- sion processing material at strains ε~ 3.5 and ε~ 5.5 is dis- cussed. It is found that processing does not produce any dras- tic changes in deformation structure and the microstructural refinement is slow. These results indicate that dynamic re- crystallization plays an important role during multi-axial compression process in this range of deformation.