Spray-Formed High-Tin Bronze—A Homogeneous Pre-Material for ${\rm Nb}_{3}{\rm Sn}$ -Based Superconductor Wire
The advantages of high-tin bronze which is produced by the innovative process "spray forming" and its commercial application in Nb3Sn superconductor wire are presented. An important decision in the processing of Nb3Sn superconductor wire after the bronze method is the choice of pre-material. As the bronze, together with the niobium, is subjected to hot and cold forming processes, homogeneous bronze pre-material is required. High-tin bronze produced by spray forming exhibits a high degree of homogeneity. Advantages of spray-formed bronze are the very fine, equi-axed grains, the homogeneous grain structure, the reduced delta phase particle size, the minimized delta phase volume fraction and the homogeneous element distribution. These advantages are given in all spray-formed bronze qualities with tin contents up to 20%. Spray-formed bronzes with tin contents of 14.5%, 15.5% and 16.0% and an additionally titanium content up to 0.3% are commercially produced and supplied to different superconductor wire manufacturers. The processing results show that the production process stability is excellent and the results of superconducting properties are reproducible. Bronzes with tin contents of 17% and 20% have also been successfully spray-formed and formed into tubes and rods. These bronzes are now subject of investigations regarding the use in future Nb3Sn superconducting magnets with increased magnetic field strength.