Cluster connectivity and medium-range order in metallic glass

Bulk metallic glasses were discovered more than 30 years ago. It has been established that, for multicomponent metallic glass alloys, the short-range order or the fundamental building block is characterized by solute-centered clusters. Over longer length scales, the clusters are packed on a fractal network forming the medium-range order. Still, there remain many questions on the structure of metallic glasses, particularly with regard to the development of short- and medium-range orders during structure evolution induced by temperature or mechanical deformation. The experimental results seem to show that during crystallization, mechanical deformation, and liquid-to-liquid phase transformation, the short-range order is enhanced but there are no substantial changes in the structure order. Rather, it is the connectivity between clusters at medium-range scale, that drives the dynamic response. In this paper, we explore the meaning of cluster connectivity and apply the concept to explain our experimental observations.