Texture and microstructure of pure Nb fabricated by cross rolling combined with differential speed rolling

Abstract

Pure niobium (Nb) sheets were subjected to a special rolling process called HRCR, which combines high-ratio differential rolling (HRDSR), which is a severe-plastic-deformation rolling method, with cross rolling (CR). During HRCR, as the thickness reduction increased, the average grain size decreased. The fraction of dynamically recrystallized (DRXed) grains was higher and the grain size was smaller in the HRCR-processed sample than that in the HRDSR-processed sample with the same thickness reduction. During HRCR rolling, the intensity of rotated cube {100} texture increased up to a thickness reduction ratio of 40% and then decreased above the thickness reduction ratio of 60%. In both α- and γ-fiber, the ODF intensity of the HRCR-processed sample was lower than that of the HRDSR-processed sample, indicating that CR weakened the texture due to the frequent change in the strain path during the process. After annealing at 1273 K, preferential recrystallization occurred on {111} grains that had higher densities of geometrically necessary dislocations and Taylor factors than {100} grains. The annealed HRCR-processed sample exhibited a random-like texture with weak α- and γ-fibers, while the HRDSR-processed sample exhibited a {100} texture and {111} γ-fibers. {110} Goss texture developed on the recrystallized grains in the HRCR-processed sample, which is known to be beneficial in improving the performance of superconducting radio frequency cavities.

Keywords

• Cross rolling
• Differential speed rolling
• Texture
• Grain refinement
• Taylor factors
• Microstructure