Bubbloy” is latest Caltech invention

First there was liquid metal, that wondrous substance from Bill Johnson’s materials science lab that is now used to make golf clubs and tennis rackets. Now a couple of Johnson’s enterprising grad students have come up with a new invention—liquid metal foam.

According to Chris Veazey, who is working on his doctorate in materials science, the new stuff is a bulk metallic glass that has the stiffness of metal but the springiness of a trampoline. “You can squish it and the metal will spring back,” says Veazey, who has given the stuff the tentative name “bubbloy,” a combination of “bubble” and “alloy.” The researchers’ material was featured in an article and on the cover of Applied Physics Letters in January.

Greg Welsh, the coinventor and also a doctoral student in materials science, adds that bubbloy is made possible by a process that foams the alloy so that tiny bubbles form. Preliminary results show that if the bubbles nearly touch, the substance will be especially springy.

“We think it might be especially useful for the crumple zone of a car,” says Veazey. “It should make a car safer than one where the structures in the crumple zone are made of conventional metals.”
Bubbloy is made of palladium, nickel, copper, and phosphorus. This particular alloy was already known as one of the best bulk metallic glasses around, but Veazey and Welsh’s contribution was figuring out how to get the stuff to foam. Other researchers have previously figured out how to foam metals like titanium and aluminum, but bubbloy will have big advantages in the strength-to-weight ratio.

How good is good? Veazey and Welch’s preliminary castings result in a bubbloy that is light enough to float in water, yet is quite strong and elastic.

“To make it really well is a challenge,” Welch says.

Bubbloy was one of several advances that were showcased at the September 15 conference at Caltech titled “Materials at the Fore.” It was the third annual meeting of the Center for the Science and Engineering of Materials at Caltech.

Julia Kornfield, professor of chemical engineering at Caltech and director of the center, presented the opening remarks and an overview of the conference. Presentations included “Nano-scale Mechanical Properties,” by Subra Suresh of MIT; “Synthesis and Assembly of Biological Macromolecules: DNA and Beyond,” by Steve Quake of Caltech; “Thermoelectric Devices,” by Sossina Haile of Caltech; and others.
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