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

Abstract

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 τ 1-FeSi 2Ti and τ 2-FeSiTi are confirmed. The crystal structure of the phase τ 3-Fe 4Si 3Ti is shown to be of Pd 40Sn 31Y 13-type (space group P6/ mmm, a = 1.72073(8) nm and c = 0.79819(6) nm). Four more ternary phases, τ 5, τ 7, τ 8, and τ 9, 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 τ 4 and τ 6 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 τ 1 and τ 2, small regions of primary solidification for the phases τ 3–τ 6, τ 8 and τ 9, but none for τ 7. A reaction scheme linking the liquidus surface with the equilibria at 900 °C is proposed.