Phase equilibria in the Al–Fe–Mo system.

This paper presents the results of our comprehensive study of phase equilibria in the Al–Fe–Mo system using DTA, X-ray diffraction, SEM and electron probe microanalysis. The liquidus and solidus projections were constructed. It is shown that the ternary compound Al 8 FeMo 3 (τ) melts congruently at >1500 °C and has a homogeneity range from 2 to 9 at.% Fe and from 23.5 to 25 at.% Mo. Isostructural phases (Mo), (αFe) and AlMo (W-type structure, cI 2 -Im- 3 m) at solidus temperatures form a continuous solid solution (αFe,Mo,AlMo). Unlike the AlMo binary phase, which is not retained by quenching, the ternary (αFe,Mo,AlMo) phase is easily quenched due to its lower decomposition temperature. Among the binary based phases, the Al 8 Fe 5 (ε) phase has the widest homogeneity region, which extends up to 24 at.% Mo at solidus temperatures. It is shown that the addition of Mo stabilizes the Al 8 Fe 5 (ε) phase, and the temperature of its formation in the ternary system increases to 1331 °C in contrast to 1234 °C in the binary. Moreover, according to XRD data, the Al 8 Fe 5 (ε) phase in the ternary system has a rhombohedral structure of the Al 8 Cr 5 -type (hR 78- R -3m), rather than cubic Cu 5 Zn 8 -type structure (cI 52- I -43 m), like the binary one. A new binary compound Al 45 Mo 7 was identified for the first time. Its crystal structure is established as monoclinic Al 45 V 7 -type (mS 104- C 2/ m) with the lattice parameters a = 20.534, b = 7.561, c = 10.910 Å, β = 107.33. It was shown to form by peritectic reaction L + Al 5 Mo ⇄ Al 45 Mo 7 at ∼800 °C. Iron additions stabilize the Al 4 Mo phase, which in the binary system is stable above 942 °C. [Display omitted] • Phase relations in the ternary Al–Fe–Mo systems over the whole concentration range were studied. • A new binary compound Al 45 Mo 7 with a monoclinic Al 45 V 7 -type structure was found. • It is shown that the ternary compound Al 8 FeMo 3 (τ) melts congruently at >1500 °C. • A continuous solid solution (αFe,Mo,AlMo) (W-type structure) was found at solidus temperatures. • Fifteen four-phase invariant reactions are found,one is of peritectic type and fourteen ones are of U-type. [ABSTRACT FROM AUTHOR]