LMTO/CVM Calculations of BCC Based Phase Ordering in The System Fe-Be

Abstract

Solid lines in Figure 1 indicate equilibrium phase boundaries of the Fe-Be system¹. Dashed and dotted lines indicate metastable BCC-based phase relations (Higgins et al.² and Miller et al.³’⁴⁾. At equilibrium, one can dissolve up to 30 atomic percent Be in αFe at 1165°C, and many studies report that BCC-based ordered phases can be synthesized by annealing Fe-rich solutions at lower temperatures²’¹². There is general agreement that a metastable α”+B2 field exists at T<-600°C, and that within this field ordering proceeds by a spinodal mechanism that produces a [100] modulated structure. In addition^2-4, an α’+”metastable precipitate” field has been reported in the interval ~800°C>T>~600°C, and Miller et al.^3,4 identify the metastable precipitate phase as B32 with X=-0.49. A DO₃ phase (Fe₃Be) was reported by Davies and Richman⁷ and Boiling and Richman⁸, but others^{2-4, 9, 10} failed to reproduce their results. With the hope of clarifying the BCC-based metastable phase relations we undertook a first principles calculation of BCC-based ordering in the Fe-Be system.