Young scientists brings lifetime of passion, curiosity, hope to producing better materials for fusion energy.

Spurred by next-generation thinking, innovative uses of composite metal-ceramic 3D printing in the field of nuclear may just be the "Eureka!" moment needed to unlock one of Man's greatest accomplishments – fusion.

When Alexander O'Brien sent in his application for graduate school at Massachusetts Institute of Technology's Department of Nuclear Science and Engineering, he already had a kernel of a research idea growing.

So, when O'Brien received a phone call from Professor Mingda Li, the student from rural Arkansas shared his thoughts on the possibility of materials that could hold nuclear reactors together.

"I think you'd be a really good fit for Professor Ju Li," O'Brien recalls Li saying.

Ju Li, a Battelle Energy Alliance Professor in Nuclear Engineering, had wanted to explore 3D printing for nuclear reactors, and this young mind seemed like the right candidate.

"At that moment I decided to go to MIT if they accepted me," O'Brien said.

And they did.

Under the advisement of Ju Li, the fourth-year doctoral student has begun exploring the potential of 3D printing ceramic-metal composites and their use in the construction of fusion power plants.

Innovation from anywhere

Growing up in rural Springdale, Arkansas, as a self-described "band nerd," O'Brien already had an interest in the sciences, particularly chemistry and physics.

It is one thing to mix baking soda and vinegar to make a "volcano" and quite another to understand why a paper mâché mountain was erupting.

"I just enjoyed understanding things on a deeper level and being able to figure out how the world works," said O'Brien.

At the same time, the world presented a conundrum for him that was difficult to ignore, especially as they played out in his own backyard. When Arkansas, a place that had hardly ever seen earthquakes, began registering them in the wake of fracking in neighboring Oklahoma, it was "like a lightbulb moment" for O'Brien.

"I knew this was going to create problems down the line, I knew there's got to be a better way to do [energy]," he added.

With the idea of energy alternatives sitting in his back pocket, O'Brien enrolled for undergraduate studies at the University of Arkansas. Participating in the school's marching band, as any true band nerd would do – "you show up a week before everyone else and there's 400 people who automatically become your friends" – O'Brien started out just by enjoying the social environment that is characteristic of a postsecondary school.

Never forgetting his interests, O'Brien double-majored in chemical engineering and physics and appreciated "the ability to get your hands dirty on machinery to make things work."

In the right environment, he began exploring possible energy alternatives and started with researching metal dichalcogenides (any two atoms of the chalcogen family – Group 6a elements such as oxygen, sulfur, selenium, tellurium, polonium, or element 116) or a branch of materials that could catalyze the hydrogen evolution reaction to more easily create hydrogen gas.

It was shortly after his sophomore year, however, that O'Brien really found his way into the field of energy alternatives – nuclear engineering. The American Chemical Society was soliciting student applications for a summer study of nuclear chemistry in San Jose, California. Applying, he was accepted.

"After years of knowing I wanted to work in green energy but not knowing what that looked like, I very quickly fell in love with [nuclear engineering]," he said.

That summer cemented O'Brien's decision to attend graduate school. "I came away with this idea of 'I need to go to grad school because I need to know more about this," he added.

As part of the summer program, O'Brien recalls being especially appreciative of an independent project – of which he chose to research nuclear-powered spacecraft.

Digging deeper into his project, O'Brien discovered the challenges of powering spacecraft-nuclear was the most viable energy alternative, but it had to work around extraneous radiation sources in space.

Getting to visit national laboratories near San Jose, however, truly sealed the deal.

"I got to visit the National Ignition Facility, which is the big fusion center up there, and just seeing that massive facility entirely designed around this one idea of fusion was kind of mind-blowing to me," he said.

Fresh mind, fresh ideas

Still working on his postgraduate studies, O'Brien's current research at MIT's NSE department is equally mind-blowing.

As the designs for new fusion devices continue to advance toward stability, it has become increasingly apparent that the materials currently in use aren't capable of withstanding the force of a sun. However, 3D printing "opens up a whole new realm of possibilities for what you can do with metals, which is exactly what you're going to need [to build the next generation of fusion power plants]," O'Brien said.

By themselves, metals or ceramics might not do the job of surviving high temperatures (750 degrees Celsius or 1,382 degrees Fahrenheit is the target), stresses, and radiation, but together, it might be a different story.

Although such metal matrix composites have been around for decades, they have been impractical for use in reactors because they are "difficult to make with any kind of uniformity and really limited size scale," said O'Brien.

This is because when adding ceramic nanoparticles to molten metal, they disperse everywhere else than where they need to be.

"3D printing quickly changes that story entirely, to the point where if you want to add these nanoparticles in very specific regions, you have the capability to do that," added O'Brien.

His work, which forms the basis of his doctoral thesis and a research paper in the journal Additive Manufacturing, involves implanting metals with ceramic nanoparticles. The net result is a metal matrix composite that is an ideal candidate for fusion devices, especially for the vacuum vessel component, which must be able to withstand high temperatures, extremely corrosive molten salts, and internal helium gas from nuclear transmutation.

Most of his current work has focused on nickel superalloys like Inconel 718, which are especially robust candidates because they can withstand higher operating temperatures while retaining their strength. Despite its potential, one of the major problems facing Inconel 718 is helium embrittlement, where bubbles of helium caused by fusion neutrons lead to weakness and failure of the nickel-chromium alloy.

However, a composite of Inconel 718 shows the potential to overcome this flaw.

3D printing sun-proof materials

Materials advanced enough to withstand 100 million degrees Celsius (180 million degrees Fahrenheit) aren't something you can just knead together, even with the precision of 3D printers.

Firstly, to create composites, a mechanical milling process coats the ceramic onto metal particles. These act as reinforcing agents, especially at high temperatures, and make the material last longer. The nanoparticles also absorb helium and radiation defects when uniformly spaced, which prevents these damaging agents from passing through.

Only after this preparation does the composite begin its 3D printing process. Utilizing one of the most common printing methods, powder bed fusion – essentially a super-heated laser that melts a singular component up from a layer of powder into the desired shape – the engineers can craft around the ceramic particles and melt the metal.

"By coating these particles with ceramic and then only melting very specific regions, we keep the ceramics in the areas that we want, and then you can build up and have a uniform structure," said O'Brien.

The 3D printing of nuclear materials exhibits such promise that O'Brien is now considering pursuing the prospect beyond his doctoral studies.

"The concept of these metal matrix composites and how they can enhance material property is really interesting," he said. The possibility of scaling up such a technology commercially through a startup is certainly on his radar.

For now, though, O'Brien is still enjoying research much like he must have as a child building that volcano, but now his pastimes also include catching an occasional show with his wife. Although the band nerd doesn't pick up his saxophone much anymore, a drive up the East Coast for some backpacking fills in that space.

"That's my newfound hobby," he said. "Since I started grad school."