Probing the formation of ultrastable metallic glass from structural heterogeneity

Ultrastable metallic glasses (SMGs) exhibit enhanced stability comparable to those of conventional glasses aged for thousands of years. The ability to understand why certain alloy compositions and processing conditions generate an SMG is an emerging challenge. Herein, amplitude-modulation dynamic atomic force microscopy was utilized for tracking the structure of Zr 50 Cu 50 , Zr 50 Cu 44.5 Al 5.5 and Zr 50 Cu 41.5 Al 5.5 Mo 3 thin film metallic glasses (TFMGs) that were produced by direct current magnetron sputtering at room temperature with the rate of deposition being the only variable. The transition in stability from bulkto SMG-like behavior resides in the change of relaxation mechanism as the deposition rate is decreased. The formation of SMGs is directly linked with the degree of structural heterogeneity, whereby MGs with greater heterogeneity have a higher potential to form SMGs with more significant enhancement in stability. Slower deposition rates, however, are required to yield the more homogenous structure and lower energy state underlying the ultrastability. Ultrastability is closely linked with the geometric shape and distribution of loosely packed phases, whereby SMGs containing more slender loosely packed phases with a more skewed distribution achieve more significant improvements in stability. This work not only provides direct evidence of the structure of SMGs, but also opens new horizons for the design of SMGs. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This study investigates the structure of metallic glasses and reveals the influence of deposition rate on their stability. Structural heterogeneity and the geometric shape and distribution of loosely packed phases play significant roles in achieving ultrastability. The findings open up new possibilities for the design of ultrastable metallic glasses.