Solid solubilities in transition-metal-based f.c.c. alloys

Abstract

A new method for estimating the solubility limit of the terminal solid solution in transition-metal-based alloys has been developed on the basis of discretevariational DV-Xα cluster calculations of electronic structure. In this method, a parameter M_d, which is the average energy level of the d Orbitals of the alloying transition metal, is successfully introduced as a new parameter relevant to phase stability. This parameter involves both electronegativity and atomic size, two parameters used in the classical approach by Darken and Gurry (1953). The validity of the proposed method is shown by the examination of about 25 ternary phase diagrams at various temperatures. Compared to the previous methods developed by Hume-Rothery et al. (1934), Darken and Gurry (1953) and Chelikowsky (1979), the present method is found to be more quantitative for the estimation of solid solubilities in austenitic alloys containing transition metals. The usefulness of the method is demonstrated through its successful application to alloy design of Ni-, Co-and Fe-based superalloys. Several problems inherent in alloy design based on the electron vacancy concept are solved by using the present approach.