Experimental determination of the isothermal sections and the liquidus surface projection of the Mo-Si-Cr ternary system

Abstract

The isothermal sections at 1200 and 1000 ℃ and the liquidus projection of the Mo-Cr-Si system have been experimentally determined based on the microstructures, the phase structure analyses and the phase constitutions of the as-cast and the isothermally heat treated alloys in whole composition range, using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. In the isothermal section at 1000 and 1200 °C, five three-phase regions and ten two-phase regions were derived, and no ternary compounds were observed. Nine primary solidification regions and six univariant reaction lines were deduced based on the study on the solidification processes of the as-cast alloys in the liquidus surface projection. In addition, the stoichiometry compounds Mo5Si3 and αCr5Si3 are the phases of the same structure (W5Si3-type) but different compositions, forming two intermetallic compounds Mo-rich Mo(Cr)5Si3 and Cr-rich Cr(Mo)5Si3. The present experimental results could be used for the further thermodynamic assessment of the Mo-Si-Cr ternary system, and be helpful for the database development of the multi-components Nb/Mo-Si-based superalloy system.