Amorphization and devitrification reactions in metallic glass alloys

The devitrification of amorphous phases can be controlled to yield a high nucleation density and a nanoscale microstructure based upon either nanocrystals dispersed in an amorphous matrix or a completely nanocrystalline solid. For both rapidly solidified marginal glass forming alloys and slowly cooled bulk glass forming alloys, the high nucleation densities are related to heterogeneous nucleation reactions that are sensitive to the initial as-prepared state of the amorphous phase. Selective doping of Al based glasses, for example, can enhance the nucleation densities from 1021 to 1023 m−3. The heterogeneous nature of the local structure is reflected also in the response of amorphous alloys to deformation-induced synthesis of nanocrystals. Moreover, kinetics studies have revealed that the governing devitrification reactions often proceed under transient conditions that can lead to relatively stable and robust nanoscale microstructures.