Mechanical Properties of High RRR Niobium at Cryogenic Temperatures
High RRR niobium superconducting rf cavities are fast becoming the basic accelerator structures of a new breed of particle accelerators. Mechanical properties of the high RRR niobium play a critical role in the physical integrity of these structures. The mechanical properties, yield strength, ultimate tensile strength and percent of elongation of Nb are routinely measured at CEBAF in the temperature range 300 to 4.2 K as a quality assurance measure. In this paper the mechanical properties of high purity niobium from Fansteel and Teledyne are presented as a function of temperature between 300 and 4.2 K. As can be expected the yield and tensile properties improve with a decrease in temperature. However, a dip in the elongation versus temperature curve is observed at about 100 K. This seems to be attributable to the presence of interstitial hydrogen. A detailed investigation of the Q-degradation of the Nb cavities also observes a dip in the Q 0 versus temperature curve at about 100 K.
KeywordsUltimate Tensile Strength Electron Beam Melting High Temperature Heat Treatment Quality Assurance Measure Interstitial Hydrogen
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- 1.A summary of rf superconductivity issues and activities is given in the “Proceedings of the 5th Workshop on Rf-Superconductivity,” Hamburg 1991, Report DESY M 92–01, Deutsches Elektronen Synchrotron, Hamburg.Google Scholar
- 3.R. A. Bosch, Production of high RRR niobium discs for SURA/CEBAF, in: “Proc. of the Conf. Electron Beam Melting and Refining: State of the Art 1990, ” R. Bakish ed., Bakish Materials Corporation, Englewood (1990).Google Scholar
- 6.G. Cannelli and L. Verdini, Relaxation effect due to diffusion of interstitial hydrogen in tantalum and niobium, La Ricerca Sci. 36: 98 (1966).Google Scholar
- 8.K. Saito and P. Kneisel, Q—degradation in high purity niobium cavities: dependence on temperature and RRR values, in: “Proc of the Third European Accel. Conf.” H. Henide, H. Homeyer and Ch. PetitJean-Genaz, eds., Editions Frontiers Cedex (1992).Google Scholar
- 10.P. Kneisel, J. Mammosser, M. G. Rao and K Saito, Superconducting cavities from high thermal conductivity niobium for CEBAF, in: “Proc. of the Conf. Electron Beam Melting and Refining-State of the Art 1990, ” R. Bakish ed; Bakish Materials Corporation, Englewood (1990).Google Scholar
- 12.A. Matheisen, H. B. Peters and A. Mosnier, Mechanical properties of the 1.3 GHZ TESLA cavity, in: “Froc. of the High Energy Accelerator Conference,” J. Rossbach ed., World Scientific, New Jersey (1993).Google Scholar