Liquid structure and long range diffusion: Their impact on glass formation and nanoscale devitrification

The importance of liquid structure on phase formation is illustrated by recent high-energy X-ray diffraction studies of metastable liquids in the deeply supercooled state, and of transient solid phases that form during solidification. In addition, these results confirm a half-century-old hypothesis made by Frank and call into question the capability of the classical theory of nucleation to accurately describe such complex coupled nucleation processes. The addition of as little as 0.5 at.% of Ti in AlFeY alloys radically alters glass formation and crystallization. This microalloying effect is argued to arise from subtle changes in the structure of the liquid/glass with the addition of Ti. Long-range diffusion is often key in the crystallization of glasses that form nanostructures. A novel mechanism for nanoscale devitrification is discussed that is based on a nucleation model that couples the interfacial and long-range diffusion stochastic processes.