Since his postdoctoral days at MIT, Hang Yu, associate professor of materials science and engineering, has been wrestling with the challenge of creating a shape-memory ceramic that can be manufactured at scale without breaking. Now, in tandem with Ph.D. student Donnie Erb ’15, M.S. ’18 and postdoctoral researcher Nikhil Gotawala, he’s had a breakthrough.
Yu’s team has used an advanced manufacturing technique called additive friction stir deposition to embed functional ceramic particles into metal. The result? A strong, defect-free material that can phase-shift under stress to dissipate energy and, unlike normally brittle ceramics, can be 3D-printed in bulk with full density in the as-printed state, opening up possibilities for practical applications in defense, infrastructure, aerospace, and even high-performance sporting equipment.
The team’s original research was published in Materials Science and Engineering R: Reports, with Erb, the recipient of Virginia Tech’s prestigious Pratt Fellowship, as lead author.
“This composite can afford tension, bending, compression, and absorb energy through stress-induced martensitic transformation,” said Yu. “In that sense, it’s multifunctional. That allows us to move toward making big things with the potential for real applications.”
Unlocking new potential for brittle ceramics
Yu’s team isn’t the first to try to crack the code of shape-memory ceramics, materials that change their internal structure in response to stress or heat, then return to their original shape. They’re useful because they can move or absorb energy without gears or moving parts — a trick seen in metals like nickel-titanium alloys. But getting ceramics to play along has been a tougher nut to crack.
“When I was a postdoc, my advisor’s group published a Science paper showing that if you make this material at microscale, the brittleness of ceramics is not a major problem, and you can see the shape memory effect,” Yu said. But no one could figure out how to scale up a shape-memory ceramic so it could have structural applications. It always broke apart.
The new approach embeds tiny shape-memory ceramic particles into metal, “like putting chocolate chips into cookie dough,” Yu said. The mixture is then fed into an additive friction stir deposition machine, an advanced manufacturing tool that spins raw materials fast enough that they meld together without melting. The resulting composite metal contains evenly distributed ceramics that can shift without breaking the whole structure.
“For the first time, this research creates bulk shape-memory ceramic–metal matrix composites using a scalable, solid-state 3D-printing process,” Yu said.
Stronger materials, smarter applications
With this first demonstration of stress-induced phase transformation at a visible, bulk scale, the new material may bridge the gap between academic innovation and real world applications in industry, such as vibration damping or impact absorption in defense systems, aerospace, infrastructure, even sporting goods.
For instance, a ceramics-embedded metal could be used in the shaft of a golf club to reduce vibration while maintaining a light weight. “With this composite, you’re adding functionality to a metal that already works for a certain application,” said Erb.
It is, he added, “a ‘Field of Dreams’ situation, where if we make it, someone will find some interesting applications for it. People have shown this material works in micrometer size. We’re saying, ‘Now you can have however much of it you want.’ We’ve realized a different scale for it.”
Advanced manufacturing growth
The new research highlights Virginia Tech’s role as a powerhouse of advanced manufacturing research. Yu, an affiliate of the Virginia Tech Made: The Center for Advanced Manufacturing, has been investigating uses for additive friction stir deposition with past support from the National Science Foundation and the U.S. Army Research Laboratory.
“This composite is so interesting, and this shape-memory function of ceramics is something I have been working on since I was a postdoc. Now I’m mostly known for additive friction stir deposition. Now I can merge both these interests together and make some new key applications, and that’s very exciting.”
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