Construction of a New Method for the Design of Transition-metal-based Alloys with the Aid of a d-electrons Theory

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A new method was proposed for the design of transition-metal-based alloys with the aid of a d-electrons theory. Two alloying parameters were obtained theoretically by the DV-Xalpha molecular orbital calculation. One is the bond order (Bo) that is a measure of the covalent bond strength between atoms and the other is the d-orbital energy level (Md) that is related to the electronegativity and atomic radius of elements. The alloys studied in this research were Ni-, Fe-, Zr, - Nb- and Mo-based alloys, all of which are important for high-temperature structural applications. The results obtained are summarize as follows ;(1) Ni-based alloys : A concept of "alloying vector" was newly introduced and used for the prediction of both the chemical composition and the volume fraction of the gamma phase in alloys. Here, the alloying vector is strictly defined by using the two alloying parameters, Md and Bo. On the basis of the alloying vectors, some superalloys for jet engines and electric power plants were designed successfully. (2) Fe-based alloys : It was found that the phase stability of the alloys could be predicted using a Md-Bo diagram. Also, high temperature properties in ferritic alloys were predicted using the Bo parameter. Based on these results, ferritic alloys were designed for turbines and boilers in electric power plants. New austenitic alloys were also designed for the first breeder reactors. (3) Zr-, Nb- and Mo-based alloys : From the experimental data and the electronic calculations, some guiding principles were obtained for the design of nuclear power plants.