Evaluation of Texture and Grain Size of Nanograined Copper Produced by the Accumulative Roll Bonding Process
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INTRODUCTION
MUCH effort has been made to produce ultra-finegrained (UFG) metallic materials with submicrometer grain sizes, since UFG materials are expected to have superior performance properties. The severe plastic deformation (SPD) process is a promising way in which to produce UFG materials with bulky shapes.[1] The SPD can be explained as deformation to large strains below the recrystallization temperature without intermediate thermal treatment.[2] The accumulative roll bonding (ARB) process developed by Saito et al.[3] is a process used to impose severe plastic strain in materials without changing the specimen dimensions. Figure 1 illustrates the principle of ARB process. The ARB process consists of rolling sheets, cutting them, stacking, and then roll bonding. By repeating this procedure, very high strains have been introduced into different metals and alloys, and as a result, significant structural refinement has been achieved.[4–6] X-ray diffraction (XRD) is a powerful nondestructive method for analysis of the microstructure of materials. Microstructural parameters such as grain size and lattice strain can be estimated by XRD line profile analysis using different model-based approaches, such as Scherrer analysis, the integral breadth method, and the Williamson–Hall technique.[7] It has been shown that the evolution of texture during the ARB process is different from that in conventionally rolled samples.[8] The textural evolution of ARB-processed samples was investigated in a central region MAHNOOSH SHAARBAF, Graduate, and MOHAMMAD REZA TOROGHINEJAD, Associate Professor, are with the Department of Materials Engineering, Isfahan University of Technology, 8415683111, Isfahan, Iran. Contact e-mail: [email protected] Manuscript submitted February 14, 2008. Article published online May 23, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
of pure Al, Al alloys, and interstitial-free (IF) steels. For example, Heason and Prangnell[9] have shown that most of shear texture in pure Al rotated to C ({112}h111i) and S ({123}h634i) texture when incorporated into the center during ARB. It was shown by Chowdhury[10] that after the second cycle of ARB with an Al-Li alloy, there was formation of Brass ({011}h211i), S ({123}h634i), and Goss ({011}h100i) components, and fairly uniform b-fiber components were observed after a third cycle. However, surface textural evolution of ARB-processed copper has not been investigated. In the present study, we examined the textural evolution in ARBprocessed copper after various numbers of cycles, and the Williamson–Hall technique was used to estimate the grain size of ARB-processed copper, which was compared with results obtained earlier by transmission electron microscopy (TEM).[11] II.
EXPERIMENTAL PROCEDURE
A. ARB Process In the present study, tough pitch copper (99.9 pct purity) was used as the starting material for the ARB process. The dimensions of the starting material were 300 mm 9 30 mm 9 1 mm. Pieces of the sheets were degreased by acetone and wire brushing to remove surface contam
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