Calculation of multi component phase diagrams for niobium alloys

The thermodynamic calculation of phase diagrams for binary, ternary and quaternary niobium alloys based on the Nb-Al-Cr-Ti system is illustrated over a wide range of temperatures and compositions. In addition Scheil Simulation of the freezing of quaternary alloys is used to show how the method can be applied in practice to anticipate segregation during casting of Nb alloys. Calculation of the Nb-Cr-Mo isotherm at 1200C shows how an ‘unexpected’ miscibility gap, noted in the 1981 symposium could have been predicted. Finally, the current capability of using the CALPHAD method and the Thermo-Calc databases and software to extend such calculations to a wider range of multicomponent Nb alloys is considered. (AU)