Phase relationships investigation of the Al-Ti-La ternary system

Abstract

Phase relationships of Al-Ti-RE (rare earth elements) systems play an important role in the development of grain refiners for aluminum alloys. In the present work, the liquidus projection (>60 at% Al) and the isothermal section at 773 K (>20 at% Al) of the Al-Ti-La system have been determined. Ten primary precipitation fields were identified by the analysis of the as-cast microstructures: Al2La, γ-TiAl, Al7La3, ζ-Ti2+xAl5−x, α-Al11La3, β-Al11La3, ε(ht)-TiAl3, ε(rt)-TiAl3, τ (Al20Ti2La) and (Al). Seven type II and two type III ternary invariant reactions are proposed. The stability of five three-phase regions and seven binary compounds, α2-Ti3Al, γ-TiAl, ε(rt)-TiAl3, AlLa, Al2La, α-Al11La3, (Al) and one ternary compound τ at 773 K has been confirmed by a combination of scanning electron microscopy, energy dispersive spectroscopy, electron probe microanalysis and X-ray diffraction.