Researchers at two California laboratories have developed a metallic glass that has more resistance to bending and breaking than many types of steel.
Robert O. Ritchie in his lab at Lawrence Berkeley Laboratory.
Researchers at two California laboratories have developed a metallic glass that has more resistance to bending and breaking than many types of steel (Nature Materials, doi:10.1038/nmat2930).
The “palladium glass,” which has a chemical formula of Pd79Ag3.5P6Si9.5Ge2, has the best combination of strength and toughness seen in any class of materials, says Robert O. Ritchie of the Lawrence Berkeley Laboratory and the University of California at Berkeley (U.S.A.).
Materials scientists define “strength” as a metal’s resistance to deformation and “toughness” as its ability to resist cracking or breaking. This glass, made like other glasses—by melting the ingredients together and cooling the product quickly—demonstrated an ability to shield itself from a crack induced by the researchers.
Researchers have studied metallic glasses for more than 30 years. Although materials that are either tougher or stronger than the new palladium glass exist, this substance is the best-yet combination of the two properties, according to Ritchie.
The team chose palladium as the major ingredient because of its high ratio of bulk modulus to shear modulus, and the silver slowed down the crystallization process, leading to an amorphous mix.
Marios D. Demetriou, a California Institute of Technology postdoctoral fellow who made the glass, says that the palladium-based material conducts electricity like a metal, despite the presence of two semiconductors and phosphorus. However, because it is an amorphous “frozen liquid” rather than a crystal, its electrical resistivity is roughly twice that of the metals in their crystalline state.
The tough glass is not transparent at visible wavelengths. Instead, it has the silvery-gray color of polished aluminum.
“Optically, the Pd glass would definitely make a wonderful mirror,” Demetriou says. “Also, if toughness is required in addition to good optical properties, then this glass would make an ideal mirror. However, a very high toughness should be a top requirement, in order to justify its high cost, as compared to other lower-cost metallic glasses with similar optical properties but lacking toughness.”
Patricia Daukantas is a freelance science writer who specializes in optics and photonics.