Study of interdiffusion and growth of topologically closed packed phases in the Co–Nb system

Interdiffusion study of the Co–Nb system is conducted to determine the diffusion parameters in different phases. The integrated diffusion coefficients at different temperatures are calculated for the Nb2Co7 phase, which has very narrow composition range. The interdiffusion coefficients at different compositions in the NbCo2 Laves phase are determined. The interdiffusion coefficient in this phase decreases with increasing Nb content to the stoichiometric composition. Further, the average interdiffusion coefficient in the N6Co7-μ phase is determined. The activation energies for diffusion in different phases are calculated, providing valuable information regarding the diffusion mechanism. In addition, an experiment using Kirkendall markers is conducted to calculate the relative mobilities of the species.