ON THE STRUCTURE AND CRITICAL CURRENTS OF Nb3Sn.

This study deals with the structure and critical currents of Nbv//3Sn diffusion layers resulting from the interaction of pure niobium with a bronze melt (Sn plus 30% Cu) at 850 and 900 degree C. By varying the heat treatment time, layers of different thickness are produced. There is always a surface layer of coarse crystals formed by deposition from the melt. This layer makes only negligible contributions to the critical current. The integral critical current is shown to be maximum when the layer thickness is 20-30 micrometer and reaches 450 amp/mm in a field of 6 T at 4. 2 K. The behavior of the critical current and critical current density as a function of annealing temperature and time is discussed.