Structure and Mechanical Properties of Bimetal Nb/Cu Rods for Production of Nb3Sn Superconductors

To construct magnetic systems in modern high-energy physics projects, such as creation of the Future Circular Collider (FCC) and modernization of the Large Hadron Collider (HL-LHC), Nb3Sn superconductors with a high level of electrophysical properties, above all being a high current carrying capacity, are requisite. Such multifilament Nb3Sn superconductors are obtained by the technique of internal feeding of tin (IFT), consisting in deformation of a composite including high-purity niobium, copper, and tin to make a wire smaller less than 1 mm in diameter. The presence of such components as tin-based alloys or pure tin with Tm = 232°C in the composite wire composition precludes the possibility of Nb recrystallization annealing, which imposes strict requirements on the Nb mechanical properties, which determine the Nb capability for plastic deformation. In the study, the influence of the design and conditions of creating bimetal Nb/Cu rods on the grain structure of niobium and the state of the boundary between it and a copper sheath is discussed. The mechanical properties of rods at different steps of their fabrication are investigated. The results will be applied in development of the technological conditions of manufacture of Nb3Sn superconductors by the IFT technique.