Nano Grained Pure Copper With High Strength Produced By Ecar Process

Journal of Materials Processing Technology 211 (2011) 1085–1090

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Journal of Materials Processing Technology
journal homepage: www.elsevier.com/locate/jmatprotec

Nano-grained pure copper with high-strength and high-conductivity produced by equal channel angular rolling process
Asiyeh Habibi ∗ , Mostafa Ketabchi, Mohammad Eskandarzadeh
Departmentof Mining and Metallurgical Engineering, Amirkabir University of Technology, Hafez Street, Enghelab Avenue, Tehran, Iran

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Equal channel angular rolling, based on the equal channel angular pressing, is a severe plastic deformation process which can develop the grains below 1 m in diameter. Microstructure, mechanical properties and electricalconductivity of commercial pure copper strips processed by equal channel angular rolling were investigated. Scanning electron microscopic micrographs of the strips produced by ten passes of equal channel angular rolling process showed nano-grains ∼70–200 nm in size. Also yield and tensile strengths and microhardness of samples increased with increasing the number of passes, whereas their ductilitydecreased. The electrical conductivity varied slightly. So via equal channel angular rolling process and by producing nano-grained pure copper, the strips can be strengthened with a little decrease in electrical conductivity but it has shortcomings of low elongation and strain hardening. © 2011 Elsevier B.V. All rights reserved.

Article history: Received 14 September 2010 Received in revised form 7December 2010 Accepted 10 January 2011 Available online 18 January 2011 Keywords: Nano-grained copper Equal channel angular rolling Severe plastic deformation

1. Introduction According to the fast developments in electronic industries, there is a great demand for high-strength and high-conductivity materials. The alloyed copper is the most widely used material in this respect. The electricalconductivity of these materials is inherently lower than unalloyed counterpart. To resolve this problem ultra-fine grains (UFG) or nanostructure commercial pure copper, can be used. This goal can be obtained by severe plastic deformation (SPD) processes (Hosseini and Daneshmanesh, 2009). Among these techniques, equal channel angular pressing (ECAP) is highly effective in fabricating various UFGmaterials. ECAP process involves the induction of severe shear deformation to materials by passing them through a die where two equal channels having the same cross-sectional area are intersected at a certain angle (Lee et al., 2003; Kim et al., 2009; Horita et al., 2001). The application of ECAP to bulk solid produces grain refinement to the sub-micrometer or nanometer level (Han and Langdon, 2005; Han etal., 2002). However, the obtained structures are usually kind of a cellular type with high-angle misorientations (Alexandrov et al., 1997). Under the appropriate die geometry, more than 100% of the shear strain can be induced to the material, even at a single pass through the ECAP die (Lee et al., 2001). Recently, the method of equal channel angular rolling (ECAR) which is based on ECAP, providesrepeated shear deformation on strip metals (Jin et al., 2004; Cheng et al., 2007). In this process, by

the use of feeding roll, the work piece is fed into the die. Using this process makes continuous operation achievable (Lee et al., 2003). This process leads to improvement in toughness as well as strength (Park et al., 2004). Dalla Torre et al. (2004) fabricated ultra-fine grained pure coppersof 200 nm in size by the equal channel angular extrusion (ECAE) and showed that the mechanical properties (ultimate tensile strength and yield strength) and hardness reach a maximum after four passes and then decrease with number of passes. Han et al. (2008) applied intermediate annealing to pure copper during cyclic ECAP and reported increasing in strength and achievement in nano-grained...