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.