Multifilamentary Nb–Zr and V–Ti superconducting alloys prepared by diffusion reaction between constituent pure-metal subelements

Abstract

We have succeeded in making a superconducting Nb-Zr and 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 third element addition was also performed by replacing the constituent subelements with the third pure-metal subelement in the monofilament; Nb-Zr-V, Nb-Zr-Ti and V-Ti-Ta. Three kinds of heat treatment were investigated; (1) an alloying heat treatment (HT alloy ) which is carried out at the final size ('fs-HT alloy '), (2) HT alloy is followed by cold-working (W) down to the final size ('HT alloy + W'), and (3) an intermediate precipitation heat treatment (HT prec ) is carried out during the W stage coming after the HT alloy stage ('HT alloy + W + HT prec + W'). The 'HT alloy + W + HT prec + W' treatment was found to be most effective in enhancing the critical current densities for both Nb-68 at.% Zr and V-60 at.% Ti-9 at.% Ta alloys, despite the HT prec treatment having slightly degraded the critical magnetic field.

Superconductivity and Microstructure of v-Ti Alloy Multifilament Prepared by Diffusion Reaction Between Constituent Pure-Metal Subelements

“…Cross-sectional images of (a) a Ta sheath monofilament including of 83 V and 158 Ti puremetal subelements (V-60at%Ti) and (b) its multifilament [6]. This avoids an undesirable configuration of V-V and Ti-Ti nearest-neighbor pairs in the monofilament and allows to diffusion-react completely V-Ti pairs in a short time and enhance the J c of V-Ti filaments.…”