Liquidus Projection of the Al-Ta-V System

Phase equilibria in the Al-Ta-V system have an important role for designing Al-containing refractory multiprincipal element alloys. In order to improve the available data related to this system and contribute to the development of alloys with good microstructural stability and oxidation resistance, the liquidus projection of the Al-Ta-V system is reported for the first time in the present work. The experimental investigations were carried out via microstructural characterization of thirty-one as-cast alloys using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffractometry (XRD). The primary solidification field of BCC is preponderant in relation to those of the other phases. No microstructural signs of phase separation were observed between the isostructural VAl 3 and ( ε )-TaAl 3 phases, which suggest a MeAl 3 solid solution connecting the Al-Ta and Al-V binary edges. Alloys in all of the primary solidification fields up to 85 at.% (BCC, σ , Ta 39 Al 69 , V 5 Al 8 , MeAl 3 ) were experimentally produced. Two class II and one type III ternary invariant reactions are suggested based on experimental data: ( U I ) Liq + σ ↔ BCC + Ta 39 Al 69 , ( U II ) Liq + Ta 39 Al 69 ↔ V 5 Al 8 + MeAl 3 and ( P I ) Liq + BCC + V 5 Al 8 ↔ Ta 39 Al 69 . Ternary invariant reactions near to the Al-rich corner are suggested based on extrapolated thermodynamic data. The reported ternary compound τ -Al 35 - 48 Ta 32 - 42 V 17 - 30 was not observed in the microstructures of the as-cast alloys obtained in the present work, suggesting that its formation occurs from a solid-state reaction.