Structural and Dynamical Changes in a Gd-Co Metallic Glass by Cryogenic Rejuvenation

TL;DR

This study investigates how cryogenic temperature cycling affects the structure and dynamics of Gd-Co metallic glass, revealing subtle atomic movements, increased heterogeneity, and changes in elastic properties through advanced x-ray scattering techniques.

Contribution

The paper provides the first detailed experimental analysis of structural and dynamic heterogeneity changes in metallic glass due to cryogenic rejuvenation.

Findings

Structural changes observed after temperature cycling.

Increased Gd atom concentration inhomogeneity.

Broadened acoustic excitation indicating elastic heterogeneity.

Abstract

To experimentally clarify the changes in structural and dynamic heterogeneities in a metallic glass (MG), Gd65Co35, by rejuvenation with a temperature cycling (cryogenic rejuvenation), high-energy x-ray diffraction (HEXRD), anomalous x-ray scattering (AXS), and inelastic x-ray scattering (IXS) experiments were carried out. By a repeated temperature change between liquid N2 and room temperatures 40 times, tiny but clear structural changes are observed by HEXRD even in the first neighboring range. Partial structural information obtained by AXS reveals that slight movements of the Gd and Co atoms occur in the first- and second-neighboring shells around the central Gd atom. The concentration inhomogeneity in the nm size drastically increases for the Gd atoms by the temperature cycling, while the other heterogeneities are negligible. A distinct change was detected in a microscopic elastic property by IXS: The width of longitudinal acoustic excitation broadens by about 20%, indicating an increase of the elastic heterogeneity of this MG by the thermal treatments. These static and dynamic results explicitly clarify the features of the cryogenic rejuvenation effect experimentally.