Effects of annealing temperature on recrystallization texture and microstructure uniformity of high purity tantalum

Abstract

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 θ‐ fiber and γ‐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.