Growth behavior of Nb 3Sn layer during reactive diffusion between Cu–8.3Sn alloy and Nb

Abstract

The growth behavior of the Nb 3Sn compound during the reactive diffusion between Nb and a binary Cu–8.3 at.% Sn alloy was experimentally examined. In the experiment, (Cu–8.3Sn)/Nb/(Cu–8.3Sn) diffusion couples were isothermally annealed at temperatures of T = 923–1053 K for various times up to 1038 h. After annealing, a Nb 3Sn compound layer was observed to form at each (Cu–Sn)/Nb interface in the diffusion couple. The Nb 3Sn layer grows predominantly towards Nb but hardly towards the Cu–Sn alloy. Thus, the growth of the Nb 3Sn layer is governed by the migration of the Nb 3Sn/Nb interface. The thickness l of the Nb 3Sn layer is mathematically described as a power function of the annealing time t as follows: l = k( t/ t 0) n , where t 0 is unit time, 1 s. The exponent n is close to unity at T = 923 and 973 K and monotonically decreases from 0.96 to 0.77 with increasing annealing temperature from T = 973 to 1053 K. This means that the interface reaction in the Nb 3Sn/Nb interface is the rate-controlling process for the growth of the Nb 3Sn layer at T = 923–973 K and the interdiffusion contributes to the rate-controlling process at T = 973–1053 K. Furthermore, the volume diffusion may govern the interdiffusion at T = 1053 K, but the grain boundary diffusion will contribute to the interdiffusion at T = 923–1023 K.