Thermodynamic aspects of amorphous phase formation

The glass-forming ability of the three alloy systems Co-Zr, Cu-Zr, and Ni-Zr has been analyzed for three distinct production routes: (1) liquid quenching, (2) vapor deposition, and (3) solid-state reaction. Using the free energy and heats of formation curves obtained from the thermodynamic characterization of the respective alloy systems, a satisfactory rationale can be obtained for amorphous phase formation by all three routes. The analysis shows that while amorphous phase formation by quenching from the high-temperature liquid is clearly dependent on factors such as quench rate and the value T-G/T-M, it is the low-temperature stability of the amorphous phase relative to the other crystalline structures that enables amorphous phases to be formed by both vapor deposition and solid-state reaction. The underlying free energy curves indicate the interesting possibility of a supersaturation sequence in the nucleation of an amorphous phase by solid-state reaction. The principles underlying thermodynamic characterizations are briefly discussed, and a characterization for Co-Zr is presented.