Recrystallization of oligocrystalline tantalum deformed by cold rolling

The recrystallization behavior of coarse-grained tantalum deformed at large strains is strongly dependent on its deformation microstructure. In this regard, a longitudinal section of a high-purity coarse-grained tantalum ingot obtained by double electron-beam melting (EBM) was straight cold rolled to thickness reductions varying from 70 to 92% followed by annealing in vacuum at 900 and 1200 °C for 1 h. Microstructural characterization was performed in cold rolled and annealed specimens using scanning electron microscopy (SEM) in the backscattered mode (BSE), electron backscattered diffraction (EBSD), and microhardness testing. The recrystallization of individual grains is strongly dependent on their initial orientation. Recrystallization kinetics varies noticeably from one grain to another. Even after annealing at 1200 °C for 1 h, the microstructure of tantalum sections deformed to 92% predominantly consists of alternating bands of recrystallized grains with distinct size distributions and a few elongated areas marking the presence of individual grains softened by recovery. Results also show inhomogeneous in-grain and grain-to-grain spatial distributions of textures in the rolling plane.