Solidus Surface of the Mo–Fe–B System

The arc-melted Mo–Fe–B alloys with boron content up to ~41 at.% 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 Mo–MoB 1.0 –FeB ~0.8 –Fe region using our own experimental and literature data. The Mo 2 FeB 2 ternary compound has a two-phase equilibrium at subsolidus temperatures with each of the binary and unary phases from the constituent binary systems. The Mo 2 FeB 2 phase has a wide homogeneity range for metal content: 14–27 at.% Fe. A three-phase α-MoB + β-MoB + Mo 2 B region exists close to the Mo–B side of the Gibbs composition triangle. In addition, a three-phase region composed by the Mo 2 FeB 2 ternary compound and two iron modifications is shown to exist: BCC (δ-Fe) and FCC (γ-Fe). Another ternary compound, Mo x Fe 3–x B, with molybdenum content of 1.3–2.0 at.% is present at subsolidus temperatures in two structural modifications: orthorhombic (Fe 3 C-type structure) and tetragonal (Ti 3 P-type structure). The intermetallic μ-(Mo 6 Fe 7 ) phase in the Mo–Fe–B ternary system takes part in the three-phase equilibria on the solidus surface: σ-(MoFe) + μ-(Mo 6 Fe 7 ) + Mo 2 FeB 2 at 1375 ± ± 10°C, μ-(Mo 6 Fe 7 ) + Mo 2 FeB 2 + R-(Mo 2 Fe 3 ) at 1340 ± 10°C, and σ-(MoFe) + μ-(Mo 6 Fe 7 ) + R-(Mo 2 Fe 3 ) at 1385 ± 10°C.