New Phacomp and its Applications to Alloy Design

New PHACOMP was developed from the calculations of electronic structure of alloys by the DV-Xa cluster method. It is based on the first theoretical approach to the solid solubility problem of alloys, both solute and solvent being transition metals. The electron vacancy number that is an important parameter in the current PHACOMP, is not used any more in the New PHACOMP. Instead, a parameter Md, which is an average energy level of d orbitals of alloying transition metals, was introduced, and used for treating of the phase stability in austenitic (y) alloys. This parameter correlates with electronegativity and atomic size, being parameters used in the classical approach by Hume-Rothery, and Darken and Gurry. The validity of New PHACOMP was proved by examining about 25 ternary phase diagrams. The constant Ed line well represents various phase boundaries such as y/y + CT, y/y + 1-1, y/y + y'(Ni3Al), y/y + D(Ni3Ti) and l//y + b(NiA1) in austenitic alloys. Our method correctly predicts the occurrence of topological close-packed (TCP) phases in practical superalloys. Seve-ral difficulties in the widely used PHACOMP based on the electron vacancy concept, were solved by the present method. New PHACOMP provides a nice tool for better alloy design not only for Ni-base, but also for Co-base and Fe-base superalloys.