Phase equilibria in the REFeB system at 1000 °C

Abstract

Phase equilibria in the REFeB system (where RE represents the total rare earth content of Indian Misch metal) at 1000 °C has been investigated at the ironrich side, up to about 40 at.% RE and about 45 at.% B, using metallography, X-ray diffraction and thermomagnetic analysis techniques. The isothermal section shows the presence of two ternary intermediate phases which have been identified as the RE 2Fe 14B (Γ) and the REFe 4B 4 (Δ) phases. At the iron end, a b.c.c. α phase has been found. The Fe 2B (β) phase has practically no solubility of RE. The Γ phase appears to have a very limited solid solubility. Both the Γ and the Δ phases are tetragonal with lattice parameters a = 8.784 A ̊ , c = 12.177 A ̊ and a = 7.106 A ̊ , c = 17.011 A ̊ respectively. The Γ phase has a Curie temperature of about 245 °C and M s ≈ 120 e.m.u. g −1. The Δ phase also shows a magnetic transition between 240 and 440 °C.