Experimental determination and thermodynamic optimization of Nb-Al-Y ternary system

Abstract

Niobium-aluminide-based alloys show excellent application potential as high-temperature structural materials. In the present work, the isothermal sections of the Nb-Al-Y system at 800 and 1050°C are constructed based on X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM). Two new ternary compounds, designated as τ-phase (Nb8Al80Y12) and ρ-phase (Nb26Al58Y16), are identified and their homogeneity ranges and crystal structures have been described. The ρ-phase can exist at temperatures within the isothermal sections of 800 and 1050°C, while the τ-phase exists at 800°C and disappears as the temperature rises to 1050°C. In addition, the primary solidification phases were also identified, and five different primary solidification phases were found. Based on the experimental data, the thermodynamic optimization of the Nb-Al-Y ternary system is carried out using the thermo-calc method. The calculated results are in good agreement with the experimental results, and a set of reasonable and self-consistent thermodynamic parameters is obtained. The results provide a basis for the design of Nb-Al-Y-based alloys and enrich the database of Nb-based alloys.