SOLIDUS SURFACE OF THE Mo–Fe–B SYSTEM

Abstract

The arc-melted Mo–Fe–B alloys with the boron content up to ~41 аt.% were studied after annealing at subsolidus temperatures by X-ray diffraction, differential thermal analysis, SEM/EMPA, and Pirani–Altertum technique for measurement of incipient melting temperatures. The partial solidus surface projection was constructed for the first time in the range Mo–MoB_1,0–FeB_~0,8–Fe based on our own experimental and literature data. The Mo₂FeB₂ ternary compound has a two-phase equilibrium at subsolidus temperatures with each of the binary and unary phases from the constituent binary systems. The Mo₂FeB₂ phase has a wide homogeneity range for the content of metals: 14–27 at.% Fe. The three-phase α-MoB + β-MoB + Mo₂B region exists close to the Mo–B side of the Gibbs composition triangle. In addition, the three-phase region composed by the Mo₂FeB₂ ternary compound with two modifications of iron is shown to exist: BCC (δ-Fe) and FCC (γ-Fe). Another ternary compound, Mo_xFe_3–xB, with molybdenum content of 1.3–2.0 at.% is present at subsolidus temperatures in two structural modifications: orthorhombic (Fe₃C-type structure) and tetragonal (Ti₃P-type structure). The intermetallic μ-(Mo₆Fe₇) phase in the Mo–Fe–B ternary system takes part in the three-phase equilibria on the solidus surface: σ-(MoFe) + μ-(Mo₆Fe₇) + Mo₂FeB₂ at 1375 ± 10 °С, μ-(Mo₆Fe₇) + Mo₂FeB₂ + R-(Mo₂Fe₃) at 1340 ± 10 °С, and σ-(MoFe) + μ-(Mo₆Fe₇) + R-(Mo₂Fe₃) at 1385 ± 10 °С.