Characterization of Crystallographic Texture and Intra-Grain Morphology in Cross-Rolled Tantalum
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TRODUCTION
CRYSTALLOGRAPHIC texture, or texture, development during rolling of bcc Tantalum (Ta) at room temperature has been studied by many authors.[1–4] Various texture components/fibers are known to stabilize during rolling of bcc metals such as a-fiber: h110i parallel to rolling direction (RD), c-fiber: h111i parallel to ND, g-fiber: h100i parallel to RD, f-fiber: h110i parallel to ND, e-fiber: h110i parallel to transverse direction (TD), and h-fiber: h100i parallel to ND. However, a-fiber and (weak) c-fiber are the main texture fibers formed under cold-rolling of Ta. Conventionally, rolling is a unidirectional deformation process in which the material experiences compression along the normal direction (ND) and extension along the rolling direction (RD). It is also understood that these stable fibers get modified by the change in the deformation mode, such as clock-rolling and cross-rolling.[5–8] Clock-rolling is defined as a process where, usually, a disk is rotated by an arbitrary angle about ND after every rolling pass, with the number of passes covering the entire angularity of the disk. Cross-rolling, on the other hand, is defined ABHISHEK BHATTACHARYYA, Modeling Engineer, R&D, and MARC ABOUAF, Director, R&D, are with the H.C. Starck Inc., 45 Industrial Place, Newton, MA 02461. Contact e-mail: abhi. [email protected] MARKO KNEZEVIC, Assistant Professor, is with the Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824. Manuscript submitted May 27, 2014. Article published online December 3, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
by a process where the disk is rotated, specifically, by 90 deg about ND after every rolling pass. In addition to overall texture measurements, grain-scale microstructural characterization has also been performed by many authors in order to understand the various localized deformation mechanisms such as localized slip activity that operate to affect the in-grain orientation changes.[9–11] The work here is a contribution toward understanding of the development of deformation texture of polycrystalline Ta through modification of the deformation path. Instead of deforming the material to an arbitrary strain during the intermediate cross-rolling process,[7] the desire here was to discern between the changing deformation path and the amount of strain. Therefore, by keeping the amount of strain fixed, the Ta material was serially deformed along RD and TD. In doing so, it was possible to determine, qualitatively, the texture formation from regular rolling process to such a special case of cross-rolling process. To the authors’ knowledge, such a study has not been carried out in the past. Furthermore, grain-scale microstructural characterization was carried out to capture the intra-grain orientation-based morphology. The results from the study were matched with the known stable components of a-fiber and c-fiber for better understanding of the formation of such intra-grain morphologies. It was attainable to do so, since the only variable in the experiment was the
