Metal alloys processed with new techniques developed at MIT are being used to produce crystal structures with dimensions one-thousandth the width of human hair that enhance billions of electronic connectors around world and are paving the way for a new generation of safer military armaments.
Department of Materials Science and Engineering head Christopher Schuh says a combination of theory and experiment underlies the breakthroughs. While technologists can turn to textbooks to predict what happens when they mix metals on the macro scale, that isn’t true for nanoscale alloys. “If I mix titanium into tungsten, I know what they’re going to do in a big crystal, but in a small crystal, they have different options,” Schuh explains.
The key insight from his research is that thermodynamics are different on the nanoscale. In a nanostructured tungsten-titanium alloy, for example, titanium can decorate the interfaces between the tungsten crystals or act as a kind of mortar between tungsten crystals. “That’s a unique configuration that is not part of our textbook approaches for how we design metals,” says Schuh, the Danae and Vasilis Salapatas Professor of Metallurgy and a MacVicar Fellow.
“We use theory to sort of guesstimate what’s going to happen when we mix metals and let them be nanostructured,” he says. “What will they assemble into? If I mix those elements into each other, what will they build? I’m trying to get them to build the brick-and-mortar structure.” Experiments and computer simulations have led to better understanding of grains, the tiny crystal structures that make up metal alloys, and grain boundaries, the interfaces between individual grains. In metals these grains can range from tens of nanometers to micrometers in width. The work has yielded a toolset for developing new alloys, using theory and computing to narrow the possible combinations, followed by experimental testing to prove out results. The outcomes are materials that are thermodynamically stable, with fine-grain structure that doesn’t change even when heated, and much greater strength.
The first generation of nanostructured nickel-tungsten coatings improved durability and performance of copper-based electronic connectors and also offered an alternative to chromium-based coatings that raise environmental concerns in their processing. The research on nickel-tungsten coatings led to a spinoff company, Xtalic, of which Schuh is a founder and chief scientist. “We make this entire bulk of copper perform better with a thin overcoat,” he says. The coatings worked so well that they enabled reduced use of gold plating on the connectors.
“There are more than 5 billion connectors that are now in service every day that have incorporated that MIT nickel-tungsten coating, and the gold footprint has been shrunk dramatically. So it’s much less resource consumption delivering the same or better performance,” Schuh says. Xtalic, which is the exclusive licensee of the MIT technology, in turn sells the patented process to manufacturers in Asia and North America. Xtalic is now working on a substitute for gold in electronic connectors.
That initial generation of nanostructured coatings, which were commercialized in 2007-08, was produced through electroplating and offered an alternative to chromium-based bumpers for trucks and coatings for machine components in addition to a substitute for traditional nickel coatings on electronics. A new group of metal alloys produced using powder processing promises thicker, bulk materials for replacing much larger structures.
Schuh’s research group is developing tougher tungsten alloys for the U.S. Army and U.S. Defense Threat Reduction Agency that could potentially replace depleted uranium, which is successful at protecting tanks and piercing armored vehicles but poses health risks. Because of its density, tungsten is considered a promising alternative to depleted uranium, but tungsten won’t have the right properties unless it can be made nanocrystalline, Schuh says.
Materials science and engineering graduate student Zachary Cordero is conducting laboratory tests of the powder-processed tungsten alloys. Initial test results have been promising. “What we’re trying to do as a group is to make bulk things with fine nanostructures. The reason we want to do that is because these materials have very interesting properties that are of potential use in many applications,” Cordero says.
Unlike the nickel-tungsten coatings, which were made through electroplating, the tungsten-titanium bulk materials are made through powder processing at high heat and pressure. Both processing techniques are time-proven at production scale, and both are considered economical. That creates an opportunity to improve existing manufacturing processes by creating designed alloys with controlled nanoscale structures without having to create whole new processes from scratch. “We’re adding value in the structure more than necessarily changing the process,” Schuh says.
“We’ve just done some of our first testing where we made bulk pieces, made them into components and tested them," Schuh adds. "So this is a few years out before it’s commercialized, but you can start to see the dots connecting.”
The nickel-tungsten thin coatings for electronics measure in micrometers (millionths of a meter), but Schuh is developing thicker materials using a process of electroforming. “We know how to make these excellent materials. You could grow them and then detach them from their substrates, sort of peel them off, and that’s called electroforming,” Schuh says.
Schuh has been working for about the past five years with lightweight metals to try to increase their strength. “There is this really big dilemma that’s in all of metallurgy, that if you want something strong, you typically use a steel, if you want something light, you typically use aluminum,” he explains. Although aluminum is three times lighter than steel, on a strength-to-weight basis, steel and aluminum are comparable. That means to bear the same load as steel, you need three times as much aluminum, so your end product is not lighter anymore. Xtalic Corporation, using Schuh’s alloys, has produced at pilot scale nanocrystalline aluminum spheres, with the weight of aluminum but the strength of steel. “These materials are record-holders for the combination of strength, low weight, and high ductility. We can form them in net-shape, so we can form components, and they are starting to be achievable at large scales and interesting shapes,” Schuh says. Applications may be possible in aerospace and transportation, where there is an interest in lowering weight without compromising safety.
Xtalic Chief Executive Officer Thomas Clay says, “Chris has a big vision and the vision is to really upgrade the material sets that we build things out of. We're a part of that, and we are commercializing the first nanostructured alloys with these really impressive material property sets. I would say the association with Chris has been tremendous, and the relationship with MIT has been great. We’re happy to be part of really changing what the world builds things out of.”
As head of the Department of Materials Science and Engineering, part of Schuh’s role is to create opportunities for faculty researchers. “I’m passionate about my own research, but I’m also passionate about theirs,” he says. His connections to industry through his own research make him aware of problems beyond metallurgy that he often refers to other MIT faculty.
“I do a lot of matchmaking,” Schuh explains. “My role is to champion everybody’s work at MIT and help them find outlets for it, help them find partners.”
His own work as a metallurgist stands on the shoulders of many, he notes. “Part of why we’ve been successful is we do know the rules of metallurgy, we do have a lot of processing methods, we do have established industries and scale-up approaches so that if you do have a new idea, you can find a way to insert it into this apparatus,” Schuh says.
Tackling major challenges
Many of the major technological challenges facing the world, including sustainability, energy, manufacturing, medicine and health care, relate directly to metals processing and materials science. “People are attracted to materials science because there are these big problems to work on of global importance," Schuh says. "There are a lot of opportunities to improve things, especially better use of resources, doing things greener, doing things leaner, use less material, lighter weight, higher value added per volume. Those are huge opportunities to really improve the way we do things. That’s what get’s me excited. It’s the combination of great science with lots of good problems that need solving. It’s a great field to be in.”
Schuh, 39, joined the MIT faculty as assistant professor in July 2002, and was promoted to associate professor in July 2005. He received tenure in July 2007, became full professor in July 2011, and department head for materials science and engineering in October 2011.
Schuh, who received his PhD from Northwestern University just 13 years ago, also has a young family. He and his wife, Leslie, have two daughters, Meredith, 6, and Kira, 3. “I couldn’t do any of the any of the things I do without them,” he says.