DETERMINATION OF THE FREE-ENERGY OF METASTABLE CRYSTALLINE AND AMORPHOUS NB-CO ALLOYS AND ITS APPLICATION TO METASTABLE PHASE FORMATION

The thermodynamic functions of the metastable and stable phases in the NbCo system are calculated on the basis of the available experimentally determined thermodynamic data by applying the CALPHAD method. In particular, the free energies of the amorphous phase and of the terminal solid solution phases are determined. They are used to describe the formation of supersaturated b.c.c. NbCo and amorphous alloys, prepared by a liquid qenching process with extreme queching rates. In addition, the precipitation of an amorphous phase from a supersaturated NbCo solid solution can be interpreted by the thermodynamic conditions and the kinetic constraints. © 1990.