Nb Tubes for Seamless SRF Cavities

Fabrication of niobium (Nb) superconducting radio frequency cavities by hydroforming is desirable because of production economy and mitigation of defects. Favorable material characteristics for hydroforming include: (a) good ductility, (b) sufficient strain hardening, and (c) microstructural homogeneity. Seamless Nb cavities are attractive because they do not contain welds. Welds can act as performance inhibitors due to defects, local chemistry changes, pits, etc. The objective of the work reported is to provide a cost-effective processing strategy involving severe plastic deformation and thermo-mechanical processing to produce uniform fine grain Nb microstructures in seamless RRR Nb tubes. An example of a successful implementation of the process is presented, which provides a fine grain size and possible texture control involving different strengths of 〈111 〉/〈100〉 component in the hoop direction. A fine grain size and suitable texture should lead to less deformation heterogeneity, better surface properties, and a lower tube failure rate from hydroforming.