Quantitative Microstructural Characterization of Thick Aluminum Plates Heavily Deformed Using Equal Channel Angular Extr
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INTRODUCTION
THE current interest in materials processed by heavy plastic deformation is largely stimulated by their unusual properties due to the presence of nanocrystalline and submicrocrystalline structures.[1] A number of new processing techniques has been proposed for structural refinement by application of multiple deformation passes.[2] One technique that has received particular attention is equal channel angular extrusion (ECAE),[1–6] in which a billet is repeatedly extruded through a die with two equal intersecting channels. Despite the fact that ECAE is an effective processing technique for attaining very high strains in bulk samples, until now it has mainly been used only on the laboratory scale, mostly for producing and studying comparatively small bar and rod samples. A promising development of the ECAE technique is its recent adaption for processing of plate samples.[3,6–10] Large plates obtained by ECAE can be either used directly for O.V. MISHIN, Senior Scientist, formerly with Materials Research Department, Risø National Laboratory for Sustainable Energy, Roskilde, Denmark, is now with the Danish-Chinese Center for Nanometals, DTU Wind Energy, Technical University of Denmark, 4000 Roskilde, Denmark. Contact e-mail: [email protected] V.M. SEGAL, Chief Technology Officer, is with Engineered Performance Materials, Whitmore Lake, MI 48198. S. FERRASSE, Principal Engineer, is with Honeywell International, Morristown, NJ 07962. Manuscript submitted December 16, 2011 Article published online July 6, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
various applications or can be subjected to additional forming operations, e.g., rolling, for which the plate geometry is particularly suitable. It is obvious that in order to obtain long strips or sheets from ECAEprocessed plates by rolling, the thickness of these plates must be sufficiently large. Thus, processing of thick ECAE plates is expected to be especially important for potential industrial applications. It is significant that in addition to deformation routes previously used for bar and rod samples, processing of plates enables unique routes where the sample is rotated 90 deg about the plate normal. Even though plate samples are certainly more attractive in terms of industrial processing than bars and rods, there have only been very few experimental studies of ECAE plates. Moreover, in some of these publications, the extent of microstructural characterization was limited to the measurement of the average boundary spacing and to considering general morphological characteristics of the observed deformation structures.[8] Boundary misorientations have been measured in several studies of ECAE plates.[11,12] However, since these measurements were conducted only in one plane, a complete description of the boundary network formed during ECAE deformation of plates has not been provided. The aim of the current work is twofold. First, this study is aimed at conducting a detailed quantitative analysis of the microstructure in three orthogonal planes in thick aluminum plates he
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