This image shows the volume change of cerium-based metallic glass during compression, as measured by transmission X-ray microscopy. Image: Qiaoshi "Charles" Zeng.
This image shows the volume change of cerium-based metallic glass during compression, as measured by transmission X-ray microscopy. Image: Qiaoshi "Charles" Zeng.

If you freeze any liquid fast enough, even liquid metal, it becomes a glass; such vitrified metals, or metallic glasses, are at the frontier of materials science research. They have been made by rapidly cooling alloys of various metals, including zirconium, palladium, iron, titanium, copper and magnesium, and used for a variety of applications, from making golf clubs to aerospace construction. But much about them remains poorly understood.

A team including Qiaoshi "Charles" Zeng and Ho-kwang "Dave" Mao from the Carnegie Institution, among others, is trying to figure out the rules that govern the creation of metallic glasses, by studying them under extreme pressures. This kind of high-pressure research can be used to probe structure on an atomic level and reveal a material's state of order or disorder.

Crystals are structured in repeating patterns that extend in every direction, whereas glasses lack this kind of strict organization. Crystalline metals often have weaknesses at the boundaries between crystal grains, but metallic glasses lack these defects, which makes them stronger.

From a practical standpoint, this means that metallic glasses are extremely strong, hard and resistant to wear and corrosion, all of which make them good potential candidates for engineering uses such as electronics casings and medical uses such as surgical pins and stents. But so far, their creation has been a time-consuming and expensive process, because scientists lack a general theory of metallic glass. Discovering fundamental rules governing metallic glasses, in order to guide their development, could be revolutionary.

The team, which also included Carnegie's Zhidan Zeng, Stanislav Sinogeikin, Yoshio Kono, Curtis Kenney-Benson, Changyong Park, and Wenge Yang, probed glass made from alloys of the metal cerium under pressure. High-pressure researchers at Carnegie have already probed cerium alloys extensively, so they were a natural fit for this research. Their goal was to look for fundamental rules that correlate the structure and properties of metallic glasses, with the aim of aiding the discovery and synthesis of new varieties. Their findings are published in the Proceedings of the National Academy of Sciences.

"High pressure compression is an extremely powerful tool for fine-tuning both the structures and the properties of materials such as metallic glasses and for looking for information that is consistent across samples," said lead author Charles Zeng. "By accurately measuring the evolution of structure and properties during compression, we could establish a relationship between them. The more we learn about the structure-property relationship in metallic glass, the better we can predict the properties of other potential metallic glasses."

Through their work on cerium-based metallic glass, the team was able to discover a consistent rule that establishes an exact numeric relationship between the decrease in volume of metallic glass under pressure and changes in its atomic structure, as determined using advanced X-ray tools. This numeric relationship held for metallic glasses at ambient pressures, too.

"The exactness and universality of this rule we've discovered indicates that the atomic structures of metallic glasses are not totally random, even if they aren't as regularly packed as crystalline metals; they may share some predictable structural features. This is an important step in understanding what controls the formation of these materials" Zeng said.

This story is adapted from material from the Carnegie Institution, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.