Application of the cluster/site approximation to the calculation of coherent interphase boundary energies

The cluster/site approximation (CSA) is computationally less demanding than, whilst maintaining comparable accuracy to, the cluster variation method (CVM) in the calculation of configurational entropies in alloys. This computational advantage would seem particularly attractive in calculations involving multicomponent phase equilibria, phase transformation kinetics or in the calculation of coherent interphase boundary (IPB) energies. In this communication, we report some results from IPB energy calculations as a function of temperature for some prototype binary face-centered cubic-based alloy systems. The CSA calculated results are compared with those obtained from the tetrahedron and the tetrahedron-octahedron approximation of the CVM and it is demonstrated that the CSA offers comparable accuracy to the CVM in calculating IPB energies. Moreover, CSA-calculated IPB energies for (Al)/Al3Li in Al-Li and (gamma)/(gamma)ʹ in Ni-Al are also in accord with experimental data. We conclude that the CSA offers the possibility of accurately calculating IPB energies for real binary and higher order alloys, i.e., for practical applications.