Effect of cubic equiaxed grains and its Ti-stabilizing performance inNb3Sn strands**Funds: this research project was supported by the France–China Collaboration Researchcontract CNRS no. 722441 and the SUST doctoral foundation BJ07-07.

Abstract

Two kinds of multifilament internal-SnNb3Sn superconducting strands were fabricated through the RRP method, one with 2 wt% of Tialloyed in an Sn core and the other just pure Sn. Four reaction temperatures of650,675,700 and725 °C and128 h duration were applied for A15 phase formation heat treatment after a Cu–Sn alloying procedure of210 °C/50 h+340 °C/25 h. Throughthe standard four-probe technique the heat-treated coil samples were examined for the transport non-CuJC variation withapplied field B which was then used to calculate the flux pinning force variationFP–B. The samples’ phase microstructure were also observed by meansof FESEM. The obtained results demonstrate that for fully reactedNb3Sn superconductors the transport critical current densityJC is more importantly affected by the cubic equiaxed morphology than by grain dimension, due toits much stronger flux pinning performance of the morphology. Ti addition in Sn stabilizes thecubic equiaxed grains at lower reaction temperature so that the HT temperature is effectivelyreduced, the flux pinning strength is largely reinforced and thus the transport non-CuJC is substantially promoted.