The fabrication and superconducting properties of multifilamentary Nb/sub 3/Sn with a Mg-doped bronze

Technical Report · Wed Jun 01 04:00:00 EDT 1983

OSTI ID:6320035

Dietderich, D R

Multifilamentary Nb/sub 3/Sn superconducting wires were fabricated by the ''internal bronze'' process. The conductor contained 133 niobium filaments in a Cu-Sn or Cu-Sn-Mg bronze matrix which had a composition of 6.7 at. % Sn. Up to 0.62 at. % Mg was added to the bronze. The wires were aged between 650-780/sup 0/C. The Nb/sub 3/Sn formed at different rates in each wire. Near complete filament conversion to Nb/sub 3/Sn, the Mg-doped wires have much higher normalized critical currents, I/sub cNb/, (4.2K,10T) all aging temperatures. However, for some aging temperatures the I/sub cNb/ of the Mg-free wire is higher than those of the Mg-doped wires when compared at partial filament conversion, approximately 50%. When the wires with 0.62 at. % Mg and no Mg are compared at near complete reaction, the Mg-doped wire is seen to give a 100 to 150% increase in I/sub cNb/ for magnetic fields of 10T(4.2K). A 0.10 at. % Mg addition to the high tin wire does not increase the critical current density above that of the Mg-free wire for aging temperatures below 750/sup 0/C. Since the niobium filaments in the Mg-free wire have a much smaller diameter than those in the Mg-doped wire it appears that filament size, i.e., interface curvature, may play a more dominant role in the Nb/sub 3/Sn layer formation. During wire heat treatment, essentially all of the magnesium in the bronze diffuses to the Nb/sub 3/Sn layer, leaving little residue in the matrix. The magnesium distribution across the layer is not uniform; the magnesium appears to congregate at the Nb/sub 3/Sn-bronze interface. The addition of 0.62 at. % Mg to the low-tin bronze wire increases the layer growth exponent by a factor of two. This increase is associated with the change in chemical composition of the Nb/sub 3/Sn layer.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6320035
• Report Number(s): LBL-16157; ON: DE87012875
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AGING
ALLOYS
COPPER ALLOYS
CRITICAL CURRENT
CURRENT DENSITY
CURRENTS
ELECTRIC CURRENTS
FABRICATION
FILAMENTS
HEAT TREATMENTS
INTERFACES
INTERMETALLIC COMPOUNDS
LAYERS
MAGNESIUM ADDITIONS
MAGNESIUM ALLOYS
NIOBIUM ALLOYS
NIOBIUM BASE ALLOYS
SUPERCONDUCTING WIRES
TIN ALLOYS
WIRES