Microstructural study on the processing and properties of high-field A15 superconducting materials

Technical Report · Wed Aug 01 04:00:00 EDT 1984

OSTI ID:6056959

Wu, I W.D.

Superconducting properties of high-field A15 materials were studied in terms of the physical and chemical states of the A15 phases. Higher critical current is achieved through microstructural control. The A15 materials investigated include the V/sub 3/Ga and Nb/sub 3/Al phases formed by a direct-precipitation process, the multifilamentary Nb/sub 3/Sn formed by the bronze-process, and the bronze-processed Nb/sub 3/Sn with a Mg addition. The direct-precipitation process has been found to have an intrinsically inferior critical current and lower stability, due to the large effective grain size, off-stoichiometric composition, and the high stability of bcc films between A15 grains. For the bronze-processed Nb/sub 3/Sn multifilamentary wire, microscopic examination reveals that the reacted layer consists of a three-shell composite structure. A mechanism to account for the formation of this structure is proposed. The critical current density is apparently determined by the areal fraction, grain size and composition of the central, fine-grained layer. Isothermal aging at intermediate temperatures (700 to 730/sup 0/C) yields the best combination of microstructural features and the highest critical current. Double-aging treatments that start at 700/sup 0/C and finish at 730/sup 0/C improve the microstructural state of the A15 layer, and enhance the critical current density by approximately 50% at fields between 10 and 15T. Magnesium addition to the bronze matrix increases the attainable critical current density (100 to 300%) in bronze-processed multifilamentary Nb/sub 3/Sn wires as compared to the Mg-free wire at the nearly fully reacted heat treatment conditions.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6056959
• Report Number(s): LBL-16999; ON: DE85004652
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360100* -- Metals & Alloys
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AGING
ALLOYS
ALUMINIUM ALLOYS
CRITICAL CURRENT
CRYSTAL STRUCTURE
CURRENT DENSITY
CURRENTS
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
GALLIUM ALLOYS
INTERMETALLIC COMPOUNDS
MAGNESIUM ADDITIONS
MAGNESIUM ALLOYS
MICROSTRUCTURE
NIOBIUM ALLOYS
PHYSICAL PROPERTIES
SUPERCONDUCTING WIRES
SUPERCONDUCTIVITY
TIN ALLOYS
VANADIUM ALLOYS
WIRES