Tensile properties of bcc Nb-Al supersaturated solid solution embedded in a Nb matrix to be transformed to A15-type Nb3Al filaments

The mechanical Cu-cladding method is favourable to incorporate stabilizer into the rapid-heating, quenching and transformation (RHQT) processed Nb3Al conductor for NMR insert coil uses, because an appropriate mechanical deformation of bcc Nb-Al supersaturated solid solution (Nb(Al)ss) is effective in transforming it in a short time, making the resultant superconducting properties large and insensitive to the temperature ramp rate during transformation annealing. In order to examine the drawability of a Cu-clad stabilized conductor with rectangular dies that might be effective in finishing the conductor with a precision dimension, which would eventually be a key to homogenizing the magnetic field of NMR magnet, the tensile loading test at room temperature was performed for Cu-clad conductors. For comparison, the tensile properties of as-quenched wires and round-to-round deformed bare wires were also examined. A fracture elongation reached as much as 11% for as-quenched Nb/Nb(Al)ss composites, but only 3.5% for Cu-clad conductors. Effects of pre-annealing on tensile properties were also studied. Ductility does not seem to deteriorate after pre-annealing at temperatures less than 500 0C, but the pre-annealing at 600 0C apparently reduces the elongation. Pre-annealing did not improve the drawability of Cu-clad stabilized conductor with rectangular dies