(Nb,Ti)3Sn superconducting wire reinforced with Nb-Ti-Cu compound

Reinforcement of Nb3Sn wires is required for high field superconducting magnets because the Nb3Sn superconductor is very sensitive to mechanical strain and its critical current degrades drastically at a higher absolute strain than 0.3%. Recently, Nb3Sn superconducting wires reinforced with tantalum, Cu-Nb alloy and Al2O3-dispersed copper, have been developed. But, these high-strength wires do not show very high strength at an absolute strain of 0.3% because these reinforcements have a similar Young's modulus to copper. In addition, Nb3Sn layers of these wires experience an additional compressive strain caused by the differences in thermal contraction between reinforcements and Nb3Sn layers. Such a compressive strain also decreases the critical current of the wire. An intermetallic compound was selected as a reinforcement for Nb3Sn superconducting wire because such a compound is expected to have a high Young's modulus and a similar thermal contraction to the Nb3Sn compound. Fortunately, the Nb-Ti-Cu compound can be formed from the Nb-Ti and copper composite during reaction heat treatment for Nb3Sn layers. Therefore, (Nb,Ti)(3)Sn superconducting wire reinforced with the Nb-Ti-Cu compound has been fabricated. The wire shows a 0.2% proof stress of 400 MPa and maintains a critical current density equal to the unreinforced wire.