The kinetics of the reactive diffusion between a ternary Cu–8.1Sn–0.3at%Ti and pure Nb was experimentally examined in a metallographic manner. In the experiment, sandwich (Cu–Sn–Ti)/Nb/(Cu–Sn–Ti) diffusion couples were isothermally annealed at 923 to 1053K for up to 604h. During annealing, the Nb3Sn compound was produced as a layer along each (Cu–Sn–Ti)/Nb interface in the diffusion couple. The Nb3Sn layer grew predominantly towards Nb but scarcely towards the Cu–Sn–Ti alloy. This meant  that the growth of the Nb3Sn layer was governed by the migration of the Nb3Sn/Nb interface. The mean thickness l of the Nb3Sn layer was expressed as a power function of the annealing time t by the equation l = k(t/t0)n. Here, t0 was unit time, 1s. The exponent n was nearly equal to unity at 923 to 973K and monotonically decreased from 0.9 to 0.7 with increasing annealing temperature from 973 to 1053K. Thus, the interface reaction at the migrating Nb3Sn/Nb interface was the rate-controlling process for the growth of the Nb3Sn layer at 923 to 973K and the interdiffusion across the Nb3Sn layer as well as the interface reaction contributed to the rate-controlling process at 973 to 1053K. The volume diffusion in the Nb3Sn layer could govern the interdiffusion at 1053K, but the grain boundary diffusion along grain boundaries in the Nb3Sn layer will contribute to the interdiffusion at 923 to 1023K.

Kinetics of Reactive Diffusion between Cu–8.1Sn–0.3Ti Alloy and Nb. T.Hayase, M.Kajihara: Materials Science and Engineering A, 2006, 433[1-2], 83-9