Equilibrium segregation at coherent (100) interfaces in ternary fcc Systems analyzed using the cluster variation method

摘要

In order to study equilibrium segregation, composition profiles around coherent (100) interfaces in ternary fcc systems were calculated using the cluster variation method within the tetrahedron approximation. A comparison with a previous regular-solution (RS) based model was made for interfaces between two disordered phases. This RS model overestimates the maximum atomic fraction of the segregation at the interface when its bulk value is >0.1. The oscillatory decay in segregation concentration from its maximum at the interface to its bulk value is much less damped in the case of the RS model. Analysis of the damping behavior leads to a very good agreement with results from free energy expansion approximations. Finally, the CVM calculations were extended to interfaces between ordered ternary fcc phases or anti-phase boundaries. Results for the interface between the Ll_2-Cu_3Au(Ag) phase and a disordered Ag-rich phase in equilibrium at 583 K, and for a non-conservative APB in the same alloy, point to a strong suppression of order near the interfaces.