Effects of Sn concentration on the critical current density of Nb3Sn formed at the Nb–(Cu–Sn alloy) interface

Abstract

Critical current densities J_c (4 T) were measured for Nb₃Sn formed by heat treating at 700°C composite wires of single‐core Nb in various Cu–Sn alloy matrices. For given thicknesses of the Nb₃Sn layers J_c increased with increasing Sn concentration in the matrix up to the single‐phase limit of Sn in Cu. Sn concentrations in excess of 8 at.% exceed the solid solubility limit of Sn in Cu at 700°C, and the J_c of the Nb₃Sn formed when the composite is heat treated is an order of magnitude less than the J_c obtained for those samples whose Sn content is within the single‐phase limit. The highest J_c (4.0 T) was ∼1.8×10⁶ A/cm² for a 1‐μm Nb₃Sn layer formed in a 25‐mil wire with a Cu–Sn matrix composition of 7.5 at.% (13 wt%) Sn.