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The influence of equal channel angular extrusion on texture evolution in pure tantalum
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Equal channel angular extrusion (ECAE) is a forming process that gives uniform plastic deformation by simple shear to bulk material without changing the cross- sectional area of the work piece. During multiple extrusions the plane of shear deformation in the billet can be altered simply by changing the billet orientation in- between passes. Therefore a variety of different microstructures and textures can be developed in a controlled manner. The main objective of this work was to characterize deformation textures produced in pure tantalum by ECAE and to compare these to textures that arise during conventional deformation processes such as rolling and drawing. the rate of texture evolution and the influence of initial microstructure on the formation of texture were also investigated. Coarse-grained and very large grained pure tantalum was deformed by equal channel angular extrusion with different billet orientation up to -8 true plastic strain. X-ray diffraction measurements were the basis for texture analysis. Additional supporting information was obtained from optical microscopy and hardness testing. Optical microscopy revealed an increasingly worked and homogenous microstructure with increasing number of extrusion passes. After four extrusion passes microstructures of all examined materials appear uniform. The refinement of the microstructure with increased strain was accompanied by an increase in hardness. Hardness values increased most dramatically after the first extrusion pass (from 96 to 177 VHN) and were seen to increase approximately linearly with the number of extrusion passes above two. Hardness did not appear to have reached a saturation level after eight passes. Strong texture developed during processing of coarse-grained tantalum when the billet orientation was not changed. The main texture components are orientations typically found in bcc rolling textures although a rotation of approximately l 0 degrees from the ideal orientations is noticed. Processing with an alternating rotation of the billet of ±]90⁰ was found to produce some texture components found in drawn tantalum but a typical drawing texture was not seen. Multiple texture measurements indicate that the texture is homogenous throughout the full cross-section of the billet. Results further suggest that the final as-worked texture for a given extrusion route converges for the different initial microstructures examined in this study.
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Includes bibliographical references (leaves 135-137).
Issued also on microfiche from Lange Micrographics.
Leipert, Simone (1999). The influence of equal channel angular extrusion on texture evolution in pure tantalum. Master's thesis, Texas A&M University. Available electronically from
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