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NSF grant will boost knowledge of metallic glasses

Jinwoo Hwang and Gabriel CalderonJinwoo Hwang and graduate student Gabriel Calderon examine the equipment they'll use to execute a new grant from the National Science Foundation.

What do you call a metal that exhibits disordered atomic structure like that of glass? Metallic glass, of course. 

Ohio State University researchers are working to improve understanding of metallic glasses so that their hybrid properties can be utilized in a variety of consumer goods. The research is supported by a $450,000 grant from the National Science Foundation.

“Glasses are ubiquitous in nature, and many of them have superior properties to crystalline materials in terms of their utility for some important applications,” said Jinwoo Hwang, assistant professor of materials science and engineering, who leads the team.

Metallic glasses have high strength and elastic energy, meaning they can withstand higher amount of stress before they bend or break. Another important characteristic is low viscosity. When heated above glass transition temperature, the viscosity of metallic glasses becomes very low, so the material can flow very easily, which enables casting of the material in small and complicated shapes.

The unique characteristics have made metallic glasses a great candidate for nanoscale fabrication of catalysts and parts for microelectromechanical systems, cases for electronic devices, and external body parts for automobiles that require high strength.  Some metallic glasses also have high corrosion resistance, and therefore can also be used in highly corrosive environments, such as in nuclear power plants, and biomedical applications. However, the current limits of metallic glasses are tied to the poor ductility at room temperature, meaning that it is difficult to change the shape of the material without breaking it.

“Ductility is important when you want to process the material to make it into certain shapes at room temperature” Hwang explained. “It’s also important for failure resistance. For example, low ductility material will break without deforming itself, which is usually bad when you think about structural applications.”

But the deformation behavior of metallic glasses is very different from crystalline-based metals, and the origin of the unique behavior, such as shear localization, is currently not well understood. To change this, scholars need to understand their atomic structure and how that structure influences the ways glasses deform.

“Theories have suggested that the nanoscale heterogeneity involving medium range ordering, or MRO, may be linked to their important mechanical behaviors,” said Hwang. “The problem is that it’s very difficult to experimentally characterize MRO.” Because of this limitation, it still remains unclear how exactly the nanoscale structure determines metallic glasses’ unique deformation behavior.

To challenge this problem, Hwang will use a novel electron microscopy technique, called fluctuation microscopy. Fluctuation microscopy is based on electron nano-diffraction, and it is highly sensitive to MRO in disordered materials. Using the advanced electron microscopes at Ohio State’s Center for Electron Microscopy and Analysis offer new opportunities to measure the MRO structure with unprecedented precision. Hwang’s findings through microscopy will then be incorporated directly into mesoscale deformation simulations, performed by the co-investigator of the team, Professor Yunzhi Wang, which will enable realistic deformation simulation that is comparable to deformation in the real world.

“The project is a prime example of how we can create great synergy from combining two of the Department of Materials Science and Engineering’s strengths – advanced electron microscopy and computational materials science,” said Hwang. “Through this work, we’ll be able to ‘tune’ the metallic glasses’ mechanical properties by engineering their nanoscale structures, which will provide important scientific understanding on the structure-property relationships in this material and open up new commercial potential.”