1993 年 28 巻 9 号 p. 550-553
We tried to improve Jc-B properties for the multifilamentary Nb3Sn wires made by internal-tin-diffusion method. As a trial to improve Jc value under magnetic fields, two kinds of heat treatments were investigated. In conventional heat treatment (step heating) some phases of Cu-Sn bronze were synthesized at first by diffusing internal Sn below 600°C and then Nb3Sn filaments were formed at 675°C for 160h. In the new heat treatment Nb3Sn filaments were formed by rapidly putting the wire into furnace kept at 675°C (rapid heating). The Jc's in high fields of both heat-treated wires were measured at 4.2K. As a result the Jc value at 12T for the rapid-heated wire was higher than that for the step-heated wire. The superconducting transition width of the rapid-heated wire was narrower. The Nb/Sn composition ratio of the rapid-heated wire was nearer to the stoichiometry than those of the step-heated wire. It was suggested that internal Sn was diffused more smoothly to Nb filaments by this rapid heating.