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

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 degrees C are constructed based on Xray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM). Two new ternary compounds, designated as tau-phase (Nb 8 Al 80 Y 12 ) and rho-phase (Nb 26 Al 58 Y 16 ), are identified and their homogeneity ranges and crystal structures have been described. The rho-phase can exist at temperatures within the isothermal sections of 800 and 1050 degrees C, while the tau-phase exists at 800 degrees C and disappears as the temperature rises to 1050 degrees 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.