Characterization of the Formability of High-Purity Polycrystalline Niobium Sheets for Superconducting Radiofrequency Applications

Abstract The forming limit diagram (FLD) of high-purity niobium sheets used for the manufacturing superconducting radiofrequency (SRF) cavities is presented. Marciniak (in-plane) test was with blanks a thickness 1 mm and blank carriers annealed oxygen-free electronic (OFE) copper. A high formability measured, an approximate true major strain at necking plane 0.44. likely caused by its rate sensitivity 0.112. Plastic anisotropies (r-values) 1.66, 1.00, 2.30 were measured in 0 deg, 45 90 deg directions. However, stress–strain curves nominal ∼10−3 s−1 showed similar mechanical properties three Theoretical calculations (FLCs) conducted using analytical two-zone model. obtained results indicate that anisotropy affect formability. model to investigate influence on strains necking. suggest use high-speed sheet should further increase niobium.