Experimental Investigation of Phase Equilibria at 1200 °C in the Al-Nb-V System

Phase equilibria in the Al-Nb-V system are important data for the design of innovative Al-containing refractory-high-entropy alloys, however issues still open in this system. In the present work, Al-Nb-V phase equilibria at 1200 °C were re-investigated via microstructural characterization of heat-treated alloys using scanning electron microscopy, x-ray spectroscopy (EDS) and x-ray diffractometry. Results confirmed the existence of the three-phase fields BCC + Nb3Al + Nb2Al and BCC + Nb2Al + NbAl3 and the absence of ternary compounds. The solubility of binary phases Nb3Al and Nb2Al into the ternary and the stability region of the BCC solid solution were improved while the solubility of Nb in V5Al8 was confirmed negligible. In addition, VAl3 + NbAl3 diffusion couple were produced, confirming the miscibility gap between these phases and indicating the existence of NbAl3 + VAl3 + BCC equilibrium instead of NbAl3 + VAl3 + V5Al8.