Influence of Intermediate Annealing on the Nanostructure and Mechanical Properties of Pure Copper Processed by Equal Cha
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rs, ultrafine grained (UFG) and nanograined materials produced by severe plastic deformation (SPD) methods have attracted great attention since they exhibit good mechanical properties including enhanced strength and acceptable ductility.[1,2] Among the various SPD techniques, ECAP is the most applicable SHAHAB RANJBAR BAHADORI, PhD Student, and KAMRAN DEHGHANI, Associate Professor, are with the Department of Mining and Metallurgical Engineering, Amirkabir University of Technology (Tehran Polytechnic), P. O. Box: 15875-4413, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted July 31, 2014. Article published online April 30, 2015 2796—VOLUME 46A, JULY 2015
one.[3] As its name implies ECAP involves the use of a die that contains two intersecting channels of equal cross-section, which indicates the workpiece can sustain severe strains with no reduction in thickness, resulting in accumulation of very high strains. However, the work of Dalla Torre et al.[4] on the ECAP of pure copper illustrated that after four passes of ECAP, the strength reached its maximum value and the grain size remained approximately constant. Some experiments ascribed the grain refinement saturation to processes related to dynamic recovery.[5,6] To solve the mentioned problem, a novel solution was suggested by Stepanov et al.[7] They found that by performing rolling after ECAP, the strength properties increased considerably because of the decrease in the boundary spacing in accordance with the Hall–Petch relationship. Further experiments also illustrated that conducting post-rolling not only reduced the mean grain size but also decreased the grain size discrepancy throughout the workpiece, resulting in a more homogeneous structure.[8,9] Other investigations were conducted to examine the influence of post-rolling on the HSRS (high strain rate superplasticity) behavior of ECAPed UFG Al-Mg alloys.[10,11] To date, little information is available in the literature on the annealing behavior of the materials produced by ECAP. Han et al.[12] examined the influence of the intermediate heat treatment on the mechanical properties of UFG copper processed by ECAP. Molodova et al.[13] investigated the microstructural evolutions of pure copper with respect to the texture and the microstructure after performing ECAP and subsequent heat treatment. Furthermore, they probed the thermal stability of severely deformed copper in comparison to the annealing behavior of cold rolled copper.[14] However, there is no information on employing annealing treatment between ECAP and CR. The aim of this study is to consider the effects of conducting intermediate annealing at different temperatures on the nanostructure, the mechanical properties, and the texture of the samples processed by ECAP and subsequent CR. By performing an intermediate annealing at an appropriate temperature and short time the mean grain size decreases and also the yield and the tensile strength increase. The tests were conducted using copper of 99.96 pct purity received in the form of large bil
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