New fabrication technique for Nb 3(Al,Ge) composite wire

Abstract

It is an important key technology to develop the fabrication process of the Nb/Al–Ge precursor wires for the study on the RHQ-processed Nb 3(Al,Ge) wire. The increase of Ge content increases the hardness and the brittleness of the Al–Ge alloy, therefore it is very difficult to fabricate the Nb/Al–20at.%Ge precursor multifilamentary wire without frequent intermediate-annealing. Decreasing of Ge concentration in the starting Al–Ge alloy improves the cold-workability of the precursor Nb/Al–Ge composite wire. However, their T c, H c2 and J c are drastically degraded with decreasing the Ge concentration. It is cleared that the high Ge concentration of about 20 at.% is necessary to obtain excellent superconductivity through the RHQ process. Then, we studied how to make the high Ge concentration Al alloys by using gas-atomized powders. Fine Ge with sub-micron in diameter disperses in the Al alloys, and their cold-workability was improved, even though Ge concentration is more than 20 at.%. As a result, the Nb 3(Al,Ge) multifilamentary precursor wires by using the high Ge concentration alloy were successfully fabricated without intermediate annealing.