Microstructure and microtexture in pure copper processed by high-pressure torsion
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NANOSTRUCTURED MATERIALS
Microstructure and microtexture in pure copper processed by high-pressure torsion Khaled J. Al-Fadhalah • Saleh N. Alhajeri • Abdulla I. Almazrouee • Terence G. Langdon
Received: 29 October 2012 / Accepted: 29 January 2013 / Published online: 13 February 2013 Ó Springer Science+Business Media New York 2013
Abstract The evolution of microstructure and microtexture in high purity copper was examined after processing by high-pressure torsion (HPT). Copper disks were annealed for 1 h at 800 °C and later processed monotonously in HPT at ambient temperature for 1/4, 1/2, 1, and 5 turns under a pressure of 6.0 GPa. Electron backscattered diffraction (EBSD) measurements were taken for each disk at three positions: center, mid-radius, and near-edge. Results from EBSD for samples processed between 1/4 and 1 turn indicate the formation of R3 twin boundaries by recrystallization before complete microstructural refinement. The results show a gradual increase in the homogeneity of the microstructure with increasing numbers of turns, reaching a stabilized ultrafine-grained structure at 5 turns with a bimodal distribution of fine and coarse grains of 0.15 and 0.5 lm in diameter, respectively. The occurrence of recrystallization in the early straining stages was
K. J. Al-Fadhalah (&) Department of Mechanical Engineering, College of Engineering & Petroleum, Kuwait University, Khalidiya, Kuwait e-mail: [email protected] S. N. Alhajeri A. I. Almazrouee Department of Manufacturing Engineering, College of Technological Studies, PAAET, P.O. Box 42325, 70654 Shuwaikh, Kuwait T. G. Langdon Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK T. G. Langdon Departments of Aerospace and Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA
further supported by examining microtexture development with increasing numbers of turns, where this shows a gradual transition from a shear texture to a mixture of shear and recrystallization and later to a shear texture at high HPT strains. The promotion of recrystallization during HPT is probably related to the high purity of the copper.
Introduction It has been possible in the last two decades to successfully produce bulk ultra-fine grained materials by applying different processing methods of severe plastic deformation such as equal channel angular pressing (ECAP) [1] and high-pressure torsion (HPT) [2]. In HPT, a large shear strain is introduced without any significant changes in the overall dimensions of the disk, and this typically produces grain refinement in the microstructure with an average grain size in the submicron level. This provides an excellent combination of strength and ductility in metals and alloys [2]. HPT is also known as an effective SPD method due to its ability in achieving a homogeneous microstructure with greater grain refinement and an increased formation of equiaxed grains of high-angle boundaries (HABs) by co
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