The problem of grain boundary motion in the diffusion field of a solute was formulated for the case of infinitely fast diffusion along a straight boundary. The steady-state solution suggested that de-alloying occurred via 2 different modes. One was solute diffusion through the stationary boundary to the bulk. The other was diffusion-induced grain-boundary migration. The transition from one mode to the other depended upon the grain-boundary segregation coefficient. When the equilibrium concentration of the bulk solute with respect to the external gas was low, the entropy of mixing was the main driving force. Diffusion-induced grain-boundary migration did not occur in isotopic solutions because the solute atom did not segregate to the boundary. On the basis of this theory, a phase diagram in the (gas/bulk) equilibrium plane was constructed which represented the transition from diffusion-induced grain-boundary migration to alloying via stationary boundaries.

The Role of Segregation in Diffusion-Induced Grain Boundary Migration. A.Brokman, A.H.King, A.J.Vilenkin: Acta Materialia, 2001, 49[1], 1–11