Structural evolution and kinetics in Cu-Zr Metallic Liquids

TL;DR

This paper investigates the structural factors influencing glass formation in Cu-Zr metallic liquids, proposing that ideal packing and free volume management, rather than just icosahedral clusters, explain the glass-forming ability and diffusion behavior.

Contribution

It introduces a new theory emphasizing ideal cluster packing and free volume control as key to understanding glass formation in Cu-Zr alloys, challenging previous cluster-based explanations.

Findings

Ideal-packed clusters correlate with glass stability.

Structural relaxation reflects free volume evolution.

Diffusivity slowdown aligns with packing theory.

Abstract

The atomic structure of the supercooled liquid has often been discussed as a key source of glass formation in metals. The presence of icosahedrally-coordinated clusters and their tendency to form networks have been identified as one possible structural trait leading to glass forming ability in the Cu-Zr binary system. In this work, we show that this theory is insufficient to explain glass formation at all compositions in that binary system. Instead, we propose that the formation of ideally-packed clusters at the expense of atomic arrangements with excess or deficient free volume can explain glass-forming by a similar mechanism. We show that this behavior is reflected in the structural relaxation of a metallic glass during constant pressure cooling and the time evolution of structure at a constant volume. We then demonstrate that this theory is sufficient to explain slowed diffusivity in compositions across the range of Cu-Zr metallic glasses.