Mechanisms for nanocrystal formation in metallic glasses

Possible mechanisms for nanocrystal formation in metallic glasses are discussed, focusing primarily on the Al–transition metal–rare earth glasses. The presented transmission electron microscopy (TEM) data prove that nanoscale phase separation occurs prior to crystallization in some Al–RE–Ni glasses. TEM observations and modeling studies of the devitrification kinetic data for some of these glasses are presented, which demonstrate preferential nucleation of nanocrystal α-Al grains near the boundaries of the phase separated regions. Preliminary studies show no evidence for phase separation in Al–RE–Fe glasses, which also crystallize to a nanoscale microstructure. A new model for homogeneous nucleation, coupling the interfacial and the long-range diffusion fluxes, is advanced to explain this.