Phenomenological calculation of the Fe-Pd-based L1 0 -ordered phase in the Fe-Pd-Ni ternary system
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IN recent years, the application of ultra-super-critical (USC) fossil-fired power plants with higher efficiency has been accelerated by the demand of reducing CO2 emission, leading to the protection of the global environment,[1] and the requirement of high-Cr ferritic heat-resistant steels with improved creep rupture strength and steam-oxidation resistance at elevated temperatures around 923 K has been increasingly raised.[2] Igarashi et al. revealed that creep rupture strength of high-Cr ferritic heat-resistant steels was significantly improved by the addition of a few atomic percent of Pd.[3] They ascribed the origin of the strengthening mechanism to fine precipitation of an Fe-Pd–based L10 ordered phase, which has a particular crystallographic orientation relationship with respect to a bcc matrix, namely, {001}matrix//{001}L10 and 100matrix//110L10.[4,5] In addition, it was found that the effect of the addition of Pd was more pronounced at higher temperatures. A critical problem of this new heat-resistant steel with Pd, however, is the fact that Pd is quite expensive. It is, therefore, necessary to seek another inexpensive element to substitute for Pd in considering practical applications. Owing to the high cost of Pd, a computational approach is quite useful to seek the substituting elements for Pd. From the thermodynamic point of view, this is nothing but a subject of ternary phase equilibria for Fe-Pd-X systems. Unlike the case of conventional thermodynamic calculation, however, what is indispensable in the present study is the capability of deriving the information of atomic configuration to identify the substituting site of X. For this, a phenomenological calculation, which combines the cluster variation T. HORIUCHI, Researcher, is with the Department of Materials Research for Power Plants, Materials Research Laboratory, Hitachi, Ltd., Ibaraki 319-1292, Japan. M. IGARASHI, Head of Materials Science and Technology Department, is with the Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., Hyogo 660-0891, Japan. F. ABE, Director of the Heat Resistant Design Group, is with the Steel Research Center, National Institute for Materials Science, Ibaraki 305-0047, Japan. K. OHKUBO, Technical Engineer, S. MIURA, Associate Professor, and T. MOHRI, Professor, are with the Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628 Japan. Manuscript submitted July 28, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
method (CVM)[6] with empirical Lennard–Jones-type pairwise atomic interaction energies (L–J-type potentials), has been proved to be quite powerful. The free energy formula of this scheme is simple enough to be extended to ternary systems and is accurate enough to incorporate the tetragonality, which is an essential feature of an L10 ordered phase. In fact, we attempted preliminary studies for binary phase equilibria for the Fe-Pd[7,8,9] and Fe-Ni[10] systems based on the present scheme and they proved quite relia
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