Application of the cluster/site approximation to fcc phases in the Ni-Al-Cr-Re system

The cluster/site approximation (CSA) has been used to model the face-centered cubic (fcc) phases (disordered γ with the A1 structure and ordered γ′ with the L12 structure) in the Ni-Al-Cr-Re quaternary system. The CSA takes into account short-range order (SRO), which is vital for describing order/disorder transitions. The approximation possesses computational advantages over the cluster variation method while offering comparable accuracy in the calculation of multi-component phase diagrams. The CSA-calculated phase diagrams are in good accord with the experimental data. In addition, the fcc metastable phase diagrams calculated by using the CSA show the expected ordering/disordering behavior and phase relationships.