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

The constitution between 900 degrees C and 1700 degrees 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 tau(1)-FeSi2Ti and tau(2)-FeSiTi are confirmed. The crystal structure of the phase tau(3)-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, tau(5), tau(7), tau(8), and tau(9), are stable at 900 degrees 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 degrees C and 1000 degrees C, respectively. The phases tau(4) and tau(6) occur at higher temperatures and are not equilibrium phases at 900 degrees C. The liquidus surface shows wide regions of primary solidification for the congruently melting phases tau(1) and tau(2), small regions of primary solidification for the phases tau(3)-tau(6), tau(8) and tau(9), but none for tau(7). A reaction scheme linking the liquidus surface with the equilibria at 900 degrees C is proposed. (C) 2007 Elsevier Ltd. All rights reserved.