Experimental determination and thermodynamic description of the Nb-V binary system

The phase equilibria of the Nb-V binary system in the low temperature range below 850 °C have been investigated in order to determine the miscibility gap of its solid solution. By means of the approaches of the isothermal treatment of the alloys and diffusion couples as well as the differential thermal analysis (DTA), it has been proved that there is an immiscible region at low temperature, and the solid solution β (BCC_A2) separated into two phases with the same crystal structure but the different compositions, the Nb-rich βNb and the V-rich βV phases. The microstructures formed after both the spinodal decomposition and the nucleation decomposition have been observed by transmission electron microscopy (TEM). On the basis of the present experimental data as well as the related literature reports, the thermodynamic parameters of the Nb-V binary system were optimized and a 6 set of self consistent thermodynamic data was obtained. By use of the optimized thermodynamic data, the miscibility gap of the Nb-V solid solution and its spinodal decomposition range were calculated and presented.