Microstructure evolution of pure copper during a single pass of simple shear extrusion (SSE): role of shear reversal E. Bagherpour a,b,n , F. Qods a , R. Ebrahimi c , H. Miyamoto b a Faculty of Metallurgical and Materials Engineering, Semnan University, Semnan, Iran b Department of Mechanical Engineering, Doshisha University, Kyotanabe, Kyoto 610–0394, Japan c Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran article info Article history: Received 7 March 2016 Received in revised form 23 April 2016 Accepted 25 April 2016 Available online 26 April 2016 Keywords: Severe plastic deformation (SPD) Simple shear extrusion (SSE) technique Microstructure evolution Strain reversal Dislocation density abstract In the present paper the role of shear reversal on microstructure, texture and mechanical properties of pure copper during a single pass of the simple shear extrusion (SSE) process was investigated. For SSE processing an appropriate die with a linear die profile was designed and constructed, which imposes forward shear in the first half and reverse shear in the second half channels. Electron back-scattering diffraction (EBSD), transmission electron microscopy (TEM) and scanning transmission electron micro- scopy (STEM) were used to evaluate the microstructure of the deformed samples. The geometrical nature of this process imposes a distribution of strain results in the inhomogeneous microstructure and the hardness throughout the plane perpendicular to the extrusion direction. Strain reversal during the process results in a slight reduction in dislocation density, the hardness and mean disorientation angle of the samples, and an increase in the grain size. After a complete pass of SSE, dislocation density decreased by 14% if compared to the middle of the process. This suggests that the dislocation annihilation oc- curred by the reversal of the shear strain. The simple shear textures were formed gradually and the strongest simple shear textures were observed on the middle of the SSE channel. The degree of the simple shear textures decreases with the distance from the middle plane where the shear is reversed, but the simple shear textures are still the major components after exit of the channel. Hardness variation was modeled by contributions from dislocation strengthening and grain boundary strengthening, where dislocation density is approximated by the misorientation angle of LAGBs which are regarded as dis- location cell boundaries. As a result, the hardness can be predicted successfully by the microstructural features, i.e. the low-angle boundaries, the mean misorientation angle and the fraction of high-angle grain boundaries. & 2016 Elsevier B.V. All rights reserved. 1. Introduction The simple shear extrusion (SSE) technique is one of the severe plastic deformation (SPD) methods, which press the material through a specially designed direct extrusion channel [1]. By SPD methods, ultrafine-grained (UFG) metals and alloys with a grain size below 1 mm are produced. High strength but only very limited ductility in room temperature testing is the general characteristic of UFG materials [2]. Thereby these materials have extraordinary fundamental properties that could be exploited to make super- strong metals and wear-free materials [3]. Compare to the basic and familiar SPD techniques such as high pressure torsion (HPT), equal channel angular pressing (ECAP) [4] and accumulative roll bonding (ARB) [5], SSE can be very easily installed in conventional mass production systems with low cost due to the straight movement of billets or bars. A schematic representation of the SSE channel is shown in Fig. 1(a). Passing through the SSE channel the shear strain is ap- plied to the material gradually while its cross-sectional area re- mains constant. The direction of the shear is reversed after the maximum distortion with maximum distortion angle of α max at the middle plane. Another parameter of SSE processing is inclination angle (β) which has a significant effect on the deformation zone, strain rate and the load of the process [6]. The detail of the SSE process can be found in [1,7,8]. The microstructural development and mechanical behavior of commercially pure aluminum (AA1050) [1,8,9], twinning induced plasticity (TWIP) steel [10] and pure magnesium [11] after SSE processing was studied previously. The SSE process was simulated by finite element analysis to study Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2016.04.080 0921-5093/& 2016 Elsevier B.V. All rights reserved. n Corresponding author at: Department of Mechanical Engineering, Doshisha University, Kyotanabe, Kyoto 610–0394, Japan. E-mail addresses: e.bagherpour@semnan.ac.ir, gup9999@mail4.doshisha.ac.jp (E. Bagherpour), qods@semnan.ac.ir (F. Qods), ebrahimy@shirazu.ac.ir (R. Ebrahimi), hmiyamot@mail.doshisha.ac.jp (H. Miyamoto). Materials Science & Engineering A 666 (2016) 324–338