Growth kinetics of monofilamentary Nb3Sn and V3Ga synthesized by solid-state diffusion

Studies of growth kinetics of Nb3Sn and V3Ga formation have been carried for monofilamentary composites of niobium and vanadium filaments embedded in bronze wires containing varying concentrations of tin and gallium, respectively. The samples are diffusion reacted at different temperatures and for different lengths of time and the thickness and the microstructure of the resulting A-15 layer are investigated using optical and scanning electron microscopy techniques. The results are discussed in the light of the analytical model previously proposed by the present authors and it is shown that while the rate controlling step for the formation of Nb3Sn is diffusion of tin through the bronze matrix, for V3Ga it is the diffusion of gallium through the grain boundaries of the compound layer. The data are used to calculate the activation energies for Nb3Sn and V3Ga formation. (author)