The effect of heat treatment on practical multifilamentary Nb3Sn conductor

The effect of heat treatment on the practical copper-stabilized multifilamentary Nb 3 Sn conductor prepared by a "bronze" technique has been investigated. In the temperature range of 650-750°C, there is a relation of Y \propto t^{n} between Nb 3 Sn 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 Nb 3 Sn grain size follow the laws of t -0.47 and t 0.20 , respectively. The dependence of J c (bronze + Nb, same for the following.) of conductor on t is approximately parabolic. The J c (4.2K, 5T) is 2.8×10 5 A/cm 2 when t=100 hr. For another conductor, J c (4.2K, 5T) has reached 3.9×10 5 A/cm 2 . We have found that the temperature and time of heat treatment have certain influence on T c of conductor. A discussion is given to explain the foregoing results.