New fabrication approach to fine multifilamentary Nb3(Al,Ge) superconductors using an intermediate rapid quenching technique

Drawability of Nb/Al-Ge composite has been improved by a reel-to-reel intermediate rapid quenching technique. The intermediate rapid quenching is performed at an early stage of the fabrication process of multifilamentary wires to convert the coarse Al-Ge core structure into very fine microstructure. Depending on the heat treatment condition, an Al-Ge nano-structure can be obtained in the core. The hardness of the Al-Ge core is balanced with that of the Nb matrix. This technique thus allows construction of multifilamentary structure easily. In addition, it also allows an easy increase of Ge content to 25 at% in the Al-Ge core and reduction of the nonsuperconducting matrix ratio to less than 1. By a diffusion reaction heat treatment at 1400°C for the developed multifilamentary Nb/Al-Ge wire, non-Cu J_c=75 A/mm² at 21 T, 4.2 K has been obtained so far.