The effect of heat treatment on practical multifilamentary Nb3Sn conductor

The effect of heat treatment on the practical copper-stabilized multifilamentary Nb3Sn conductor prepared by a "bronze" technique has been investigated. In the temperature range of 650-750°C, there is a relation ofY \propto t^{n}between Nb3Sn layer thickness (Y) and heat treatment time(t). However, it has been found that the n values in all conductors investigated considerably differ from that reported by M. Suenaga[1] and H. H. Farrell[2]. At 700°C, for a conductor with the bronze/Nb ratio of 3.0, the variation of Sn contents in bronze matrix and that of Nb3Sn grain size follow the laws of t^-0.47and t^0.20, respectively. The dependence of Jc(bronze + Nb, same for the following.) of conductor on t is approximately parabolic. The Jc(4.2K, 5T) is 2.8×10⁵A/cm²when t=100 hr. For another conductor, Jc(4.2K, 5T) has reached 3.9×10⁵A/cm². We have found that the temperature and time of heat treatment have certain influence on Tcof conductor. A discussion is given to explain the foregoing results.