The Metastable State of Metallic Glasses

Electromotive force (EMF) measurements on amorphous CuZr and NiTi alloys demonstrate that these alloys are in a metastable state. This is concluded on the basis of a stable electrochemical equilibrium in a galvanic cell and of the reversibility of the cell reaction with respect to shorting and applying an overvoltage to the electrodes. The partial free energies of the amorphous alloys calculated from the EMF measurements are in agreement with those obtained by the CALPHAD method indicating the validity of the Gibbs-Duhem equation. Metastable amorphous phases can therefore be treated thermodynamically similar to equilibrium phases as long as crystallization is avoided during the experiment and kinetics allow to achieve the metastable equilibrium state.