耐熱合金の新しいPHACOMP (耐食・耐熱材料<特集>)

概要

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PHACOMP has been widely used for alloy development and productions in superalloy industries. It is an empirical method based on the electron vacancy concept and use electron vacancy number of transition metals, Nv, as a parameter to predict the occurence of TCP phases (e. g. σ phases) in superalloys. Although the PHACOMP is now employed as a specification for the quality control of Ni-base superalloys, there still remain some contradictions in the prediction for the occurence of TCP phases. Most of these problems are inherent in the electron vacancy concept, and hence could not be solved by several modified Nv methods so far developed. Recently, the author's group developed new PHACOMP which was based on DV-Xα cluster calculations of electronic structure of alloys. A parameter, Md, which is an average energy level of d-orbitals for alloying transition metals, was obtained for the metals of being important in superalloys. In the new PHACOMP, Md was introduced as a new parameter showing a phase stability of γ austenitic alloys, insted of Nv. In this paper, superiority of Md-PHACOMP over the traditional Nv-PHACOMP was shown through the representation of γ/γ+TCP (σ-and μ-phases) phase boundaries in Ni-, Co-and Fe-base ternary alloys by iso-Md line and the prediction of σ-phase in commercial Ni-and Fe-base superalloys.
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