Characterization of Crystallographic Texture and Intra-Grain Morphology in Cross-Rolled Tantalum

We present a detailed characterization of crystallographic texture and in-grain morphology in high purity Tantalum (Ta) during cross-rolling. A Ta disk with random initial texture was rolled to a total reduction of 50 pct in four equal steps, with the disk being rotated by 90 deg around the normal direction (ND) after every rolling step. Samples were cut along ND and were characterized using electron backscatter diffraction (EBSD), before and after the final deformation. Through-thickness texture heterogeneity was observed in the deformed disk, with an increase in < 111 > and < 100 > volume fraction parallel to ND from the surface toward the disk mid-section. The deformed texture of the mid-section of the disk (i.e., experiencing limited shear) was found to have a strong gamma-fiber and a weak alpha-fiber with presence of only {100} < 110 > texture component. From the grain-scale EBSD study, the deformed grain morphology was found to be one of the three major types: (a) un-fragmented, (b) fragmented-mottled, and (c) fragmented-banded or elongated deformation bands. The un-fragmented grains had < 111 > parallel to ND, with < 110 > parallel to the rolling direction or the transverse direction. The fragmented-mottled grains had multiple sub-grain orientations. The two major bands in the fragmented-banded grains had its < 100 > and < 111 > parallel to ND. In addition, they shared a common < 110 > with a misorientation of 30 deg. Through our knowledge of the known stable components formed during rolling of Ta, it was feasible to explain the orientations of such un-fragmented and fragmented-banded grains. (C) The Minerals, Metals & Materials Society and ASM International 2014