Nb Tubes for Seamless SRF Cavities

• Published in: IEEE transactions on applied superconductivity Vol. 23; no. 3; p. 7100904
• Main Authors: Balachandran, S., Elwell, R. C., Kang, D., Barber, R. E., Bieler, T. R., Hartwig, K. T.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.2013; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Alloys; Cavity resonators; Condensed matter: structure, mechanical and thermal properties; Crystal defects; Deformation and plasticity (including yield, ductility, and superplasticity); Electron tubes; Exact sciences and technology; Grain size; Heat treatment; Holes; Hydroforming; Inhibitors; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Microstructure; Niobium; Physics; polycrystalline; seamless tube; superconducting radio frequency (SRF) cavities; Surface layer; Texture; Tubes; Performance evaluation; Grain size analysis; High strain; Material processing; Ductility; Polycrystals; Plastic deformation; Cost; Texture; Implementation; Niobium; Defects; Weld; Cavities; Calcium nitride; polycrystalline; Surface properties; superconducting radio frequency (SRF) cavities; Thermomechanical treatments; Seamless tube; Grain size; Mechanical strength; Radiofrequency; Failure rate; Hydroforming; Granular materials; Homogeneity; Fine grain structure; Inhomogeneity; Chemical inhibition; Microstructure; Strain hardening
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2013.2243492

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.