On the reaction scheme and liquidus surface in the ternary system Fe–Si–Ti

The constitution between 900 °C and 1700 °C of the ternary system Fe–Si–Ti is investigated over the entire composition range by X-ray diffraction (XRD), differential thermal analysis (DTA), electron probe microanalysis (EPMA), and scanning electron microscopy/energy dispersive X-ray (SEM/EDX). Nine ternary phases are observed. The crystal structures for the phases τ1-FeSi2Ti and τ2-FeSiTi are confirmed. The crystal structure of the phase τ3-Fe4Si3Ti is shown to be of Pd40Sn31Y13-type (space group P6/mmm, a = 1.72073(8) nm and c = 0.79819(6) nm). Four more ternary phases, τ5, τ7, τ8, and τ9, are stable at 900 °C. Their compositions were determined, but their crystal structures are still under investigation. The tie lines observed for this temperature agree with the literature data reported for 800 °C and 1000 °C, respectively. The phases τ4 and τ6 occur at higher temperatures and are not equilibrium phases at 900 °C. The liquidus surface shows wide regions of primary solidification for the congruently melting phases τ1 and τ2, small regions of primary solidification for the phases τ3–τ6, τ8 and τ9, but none for τ7. A reaction scheme linking the liquidus surface with the equilibria at 900 °C is proposed.