SUPERCONDUCTIVITY AND MICROSTRUCTURE OF V-TI ALLOY MULTIFILAMENT PREPARED BY DIFFUSION REACTION BETWEEN CONSTITUENT PURE-METAL SUBELEMENTS.

We have succeeded in making a superconducting V—Ti alloy multifilament wire using the diffusion reaction between constituent pure-metal subelements, which can omit the melt-and-casting step and may reduce the fabrication cost. A monofilament billet prepared by restacking hexagonal Ti/V composites in a Cu/V tube and a multifilament billet by re-stacking such Cu/V/(Ti/V) composites in a Cu tube were hydrostatically extruded and drawn down to wires. Four kinds of heat treatment were investigated, with respect to mi-crostructure and superconducting properties; (1) an alloying heat treatment (HTalloy) which is carried out at the final size (‘fs-HTalloy’), (2) HTalloy is followed by cold-working (W) down to the final size (‘HTalloy+W1’), (3) an precipitation heat treatment (HTprec) is carried out after the W stage (‘HTalloy+W1+HTprec’) and (4) an intermediate HTprec is carried out during the W stage coming after the HTalloy stage (‘HTalloy+W1+HTprec+W2’). The ‘HTalloy+W1+HTprec+W2’ treatment was found to be most effective in enhancing the critical current densities (Jc), despite the HTprec treatment having slightly degraded the critical temperature (Tc) and critical magnetic field (Bc2). The highest Bc2 was obtained using the ‘HTalloy+W1’ treatment, irrespective of the HTalloy temperatures. [ABSTRACT FROM AUTHOR]