THE CRYSTAL TO GLASS TRANSFORMATION IN RELATION TO MELTING

Recent experimental studies of the crystal to glass transformation (CGT) in metallic materials are surveyed. Thermodynamic principles are used to demonstrate the relationship between CGT and ordinary melting. Polymorphic phase diagrams are employed to describe melting under conditions where atomic diffusion is inhibited. This defines the T0-curve (or polymorphic melting curve). Experimental studies of the specific heat, elastic and vibrational properties, and atomic scale structure of crystalline solids as the degree of static disorder is increased (as the T0-curve is approached) suggest a common underlying mechanism by which crystalline solids are destabilized with respect to amorphization and melting. Molecular dynamics studies of supersaturated binary solid solutions as a function of composition, atomic size ratio, pressure, and temperature have been used to further explore this problem. These results are discussed and compared with the experiments on actual binary alloys. It is concluded that the crystal to glass transformation is driven by a type of localized shear instability of the crystal.