Solidification processes of as-cast alloys and phase equilibria at 1300 °C of the Nb-Si-V ternary system

Abstract

The liquidus projection and the isothermal section at 1300 °C of the Nb-Si-V ternary system were experimentally studied. Using scanning electron microscopy, electron probe microanalysis and X-ray diffraction, the primary solidification phases and the precipitation paths in each region of the liquidus projection as well as the equilibrium relations of the phases in the isothermal section were determined. Ten primary solidification regions were found in the liquidus projection and eight three-phase equilibrium regions were observed in the isothermal section at 1 300°C. The compounds βNb5Si3 with V5Si3 and NbSi2 with VSi2 are the phases of the same structure but different compositions and form two linear compounds bNb(V)5Si3 or V(Nb)5Si3 and Nb(V)Si2 or V(Nb)Si2, respectively The ternary linear compound (Nb,V)2Si with the stoichiometry about 2:1 of (Nb + V): Si was found in both the liquidus projection and the isothermal section at 1 300°C.