Development of Ag-Barrier RHQT Nb3Al Wires

Abstract

A new type of rapid-heating, quenching and transformation-processed Nb 3 Al wire incorporating Ag-barrier structure have been developed to realize both the interfilament decoupling and the low wire breakage risk during the drawing. The barrier has a three-layered structure of Nb/Ag/Nb. Ag does not react with Nb at all even during the rapid-heating and quenching (RHQ) treatment and not penetrate into the Nb 3 Al filaments, which is necessary for maintaining the critical current density (J c ) characteristics. Drawability of the Ag-barrier Nb/Al precursor composite was excellent; a prototype 200 m wire with O1.35 mm was successfully drawn without any breakage. Ag intermediate layer allocated between the Nb layers suppresses flux jumps at low fields even at 1.8 K. It is notable that the Ag intermediate layer acts as a role of cushioning, when the wire is subject to applied strain, mitigating stress concentration inside the wire and leading to enhancement of the irreversible strain up to about 0.6%: this would be a key factor especially for the “React & Wind” magnet applications. Cu stabilizer can be easily attached through a “tube-method” after RHQ. The filament size can be reduced down to about 25 μm. The hysteresis loss (±3 T@4.2 K) per nonstabilizer volume was reduced down to 614 mJ/cm 3 .