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 constructed. Fifteen three-phase regions were confirmed, the ternary compound HfVSi was identified, and the solubilities of the third element in the binary compounds were determined. In the meanwhile, based on the XRD data obtained in the present work and by means of the JADE software package, the lattice parameters of each compound are calculated. Furthermore, the solidification paths of the Hf–Si–V as-cast 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. Particularly, transmission electron microscopy results revealed that the binary stoichiometric compound V6Si5 extended into the Hf–Si–V ternary system, forming the line compound (V,Hf)6Si5. With the decrease of temperature, the line compound (V,Hf)6Si5 can decompose into two phases, one of which V(Hf)6Si5 has the composition near V6Si5, another near Hf2V4Si5, but with the same structure type. The Hf2V4Si5 phase is proposed to form due to the miscibility gap of the line 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.