Ultralarge-scale anomalous phase separation discovered in a Cr-Fe-Co-Ni-Zr high-entropy metallic glass system

Abstract

Anomalous phase separation in metallic glasses is a longstanding issue that has been controversial since it was first implied in 1969 due to the influence of microstructure artifacts and the lack of direct large-scale (over nanoscale) evidence. This study confirms an ultralarge scale anomalous glass phase separation phenomenon in a Cr-Fe-Co-Ni-Zr high-entropy metallic glass in which any pair of atomic components has a nonpositive heat of mixing using interferencefree visible-light, atomic force, scanning electron, and double spherical aberration-corrected atomic resolution analytical electron microscopes. The second glassy phase separated from the glassy matrix has an ultralarge size of tens of micrometers, which can be controlled by the cooling rate during sample preparation. A mechanism of before-monotectic-like liquid immiscibility is introduced to interpret the phenomenon, which helps understand the anomalous phase separation in metallic glasses and in other fields, such as liquid-liquid phase separation in cells.