Microstructure development in Nb3Sn(Ti) internal tin superconducting wire
- 139 Downloads
The authors have studied the phase formation sequences in a Nb3Sn ‘internal tin’ process superconductor. Heat treatments were performed to convert the starting materials of tin, Ti–Sn, copper and niobium, to bronze and Nb3Sn. Specimens were quenched at different points of the heat treatment, followed by metallography to identify the phases present and X-ray microtomography (XMT) to investigate the void volume and distribution. An unexpected observation of the microstructure development was the uphill diffusion of tin during the Cu–Sn reactive diffusion. Some defects likely to affect the superconducting performance of the wires were observed. Microscopy revealed the presence of a Ti–Sn intermetallic compound displacing the niobium filaments, and XMT revealed the formation of long pores in the longitudinal direction. Two types of pore formation mechanism, in addition to Kirkendall pores, are proposed. The phase and microstructure development suggests that low-temperature heat treatment (below 415 °C) will have significant influence on optimising the final superconducting properties.
KeywordsCritical Current Density Heat Treatment Schedule Bronze Matrix Niobium Filament CuSnTi
Ian Pong would like to thank the Croucher Foundation, Hong Kong, and Simon Hopkins the EPSRC, for financial support.
- 2.Fischer CM, Lee PJ, Larbalestier DC (2002) In: Advances in cryogenic engineering, vols 48a and b; vol 614, p 1008Google Scholar
- 10.Godeke A (2005) Performance Boundaries in Nb3Sn Superconductors. PrintPartners Ipskamp, Enschede. ISBN 90-365-2224-2Google Scholar
- 11.Raynor GV (1944) Annotated equilibrium diagram series: No 2. The Institute of Metals, LondonGoogle Scholar
- 13.Tan KS (2006) PhD Thesis, University of CambridgeGoogle Scholar
- 14.Pong I, Hopkins SC, Fu X, Glowacki BA, Elliott JA, Baldini A (2006) Defect Diffus Forum 258–260:294Google Scholar
- 18.Scheuerlein C, Oberli L, Michiel D, Reichert K (2006) Voids in Nb3Sn strands observed by synchrotron absorption microtomography. Poster presented at the International Cryogenic Materials Conference, 17–21 July 2006, Prague, Czech RepublicGoogle Scholar
- 22.Naus MT, Jewell MC, Lee PJ, Larbalestier DC (2002) In: Advances in cryogenic engineering, AIP conference proceedings, vols 48a and b; vol 614. Amer Inst Physics, Melville, NY, ISBN 0-7354-0060-1, p 1016Google Scholar
- 24.Darken LS (1949) Trans Am Inst Minerals 180:430Google Scholar