Effects of Annealing Temperature on Recrystallization Texture and Microstructure Uniformity of High Purity Tantalum

One hundred and thirty-five degree clock rolling significantly improves the texture homogeneity of tantalum sheets along the thickness, but a distinctly fragmented substructure is formed within {111} (<111> / /normal direction (ND)) and {100} (<100> / /ND) deformation grains, which is not suitable to obtain a uniform recrystallization microstructure. Thus, effects of different annealing temperatures on the microstructure and texture heterogeneity of tantalum sheets along the thickness were investigated by X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the texture distribution along theta-fiber and gamma-fiber is irregular and many large grains with {111} orientation develop during annealing at high temperature. However, low-temperature annealing can not only weaken the texture intensity in the surface and the center layer but also introduce a more uniform grain size distribution. This result can be attributed to the subgrain-nucleation-dominated recrystallization mechanism induced by recovery at low temperature, and moreover, a considerable decline of recrystallization driving force resulting from the release of stored energy in the deformation matrix.