Interfaces and interphases in nanoglasses: Surface segregation effects and their implications on structural properties

Metallic nanoglasses can be prepared by cold compaction of amorphous nanoparticles initially condensed in inert gas atmosphere. Experimentally, it has been found that a characteristic feature of nanoglasses is the occurrence of atomic density variations within the microstructure, that cannot be explained by interface induced topological variations in a chemically homogeneous material. Here we present molecular dynamics simulations, which reveal that compositional variations between glass-glass interfaces and the volume material can result from surface segregation effects already present in the primary particles. By comparing results for Pd80Si20 and Cu64Zr36 metallic glasses, we show that amorphous nanoparticles install an inhomogenous elemental equilibrium distribution in the gas phase before they undergo the glass transition into the solid state. A detailed analysis of planar interfaces generated by merging chemically equilibrated surfaces shows that glass-glass interfaces can be understood as interphases of different composition and short-range order, where the local topology, free volume and local composition are intimately linked.