Thermodynamics of amorphous alloys

In the past, the thermodynamic state of amorphous phases has been of great concern. Due to highly non-equilibrium preparation processes involving rapid quenching and condensation techniques, it has been assumed that these alloys are frozen-in liquids where a thermodynamic description cannot be applied. Recently however, the existence of a metastable state in single-phase and phase-separated amorphous alloys has been confirmed unambiguously by electromotive force (EMF) measurements and characterized by calorimetric and structural investigations. EMF measurements also allow to directly determine the chemical potentials of the least noble component and thereby (for binary systems) the Gibbs energy of the amorphous phase. By means of thermodynamic modeling, e.g. by the CALPHAD method, phase diagrams can be calculated for the amorphous phase. These can predict the amorphous phase formation during rapid quenching of the melt and during solid-state reactions.