Phase Equilibria and Liquidus Projection Determination of the Hf–Si–V Ternary System

Abstract

The phase equilibria including the isothermal sections at 1100 and 1300 °C as well as the liquidus surface projection of the Hf–Si–V ternary system were experimentally determined. The microstructures, crystal structures and phase constitutions of the annealed and the as-cast alloys in whole composition range were investigated by means of scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction and electron probe microanalysis, respectively. The isothermal sections of the Hf–Si–V system at 1100 and 1300 °C were accordingly established. Fifteen three-phase regions were confirmed, and the ternary compound HfVSi was identified. In addition, the solidification paths of the Hf–Si–V alloys were analyzed to verify the primarily solidified phases from the liquid phase. Fifteen primary solidification regions were finally confirmed in the liquidus surface projection. Transmission electron microscopy results determined that the binary stoichiometric compound V₆Si₅ extended into the Hf–Si–V ternary system, forming theforming the linear compound (V, Hf)₆Si₅. With the decrease of the temperature, linear compound V(Hf)₆Si₅ can decompose into two phases, one of which has the composition near V₆Si₅, another near Hf₂V₄Si₅, but with the same structure type. The Hf₂V₄Si₅ phase formed due to the miscibility gap of the linear compound (V, Hf)₆Si₅. The present experimental results are useful for the thermodynamic assessment of the Hf–Si–V ternary system, and the database development for the Nb/Mo–Si–V–Hf containing multi-component superalloy materials.

Keywords: Hf-Si-V ternary system, Isothermal sections, Liquidus surface projection, solidification path, phase diagram