Scientists at Oak Ridge National Laboratory are studying how silicon carbide — one of the most temperature-resistant materials available — could be used to design and build the next generation of fusion reactors with the help of additive manufacturing technologies.
“Although SiC ceramics have long shown promise for fusion applications because of their ability to allow for more efficient energy conversion compared to other materials, such as steel, they have often been overlooked because of the challenges of building complex shapes with them,” said Takaaki Koyanagi, research staff in the Radiation Effects and Microstructural Analysis Group at ORNL and lead author of the study published in the Journal of Nuclear Materials.
“Shaping SiC ceramics into intricate shapes by conventional machining has always been very difficult because it is a very brittle material. Additive manufacturing and 3D-printing technologies are now giving us a chance to be more flexible in how we use SiC today, which is very exciting,” Koyanagi said.
Inspired by the success obtained with other materials at ORNL’s Manufacturing Demonstration Facility, Koyanagi and his team experimented with designing and 3D printing a set of small complex objects using SiC. Team members from the Transformational Challenge Reactor Program, managed by ORNL for the DOE Office of Nuclear Energy, provided support for the effort.
Their published observations are now considered the first general guidance for the development of SiC geometries that are resistant to irradiation damage, something that had not been achieved before with more traditional methods.
Promising microstructures
Even though the concepts of 3D printing and additive manufacturing have been around since the 1980s, the use of these techniques to produce highly complex ceramic objects is a new idea, and there are few guidelines for this application.
To change this, the team analyzed several additive manufacturing methods, including traditional and newer approaches, to identify the best three for developing SiC objects.
The first one, binder jetting with chemical vapor infiltration, deposits a binder between thin layers of SiC powder to build a structure layer by layer. Once completed, the item is baked at 200 degrees Celsius and subjected to filling of the porous surfaces at approximately 1,000 degrees Celsius.
Laser chemical vapor deposition, the second method proposed by Koyanagi and his team, uses a laser beam to deposit thin layers of SiC and turn them into long fibers that are 30–50 micrometers in diameter.
“Our hope is to use these fibers to reinforce other SiC matrix composites that could be used in nuclear applications,” Koyanagi said.
Lastly, the team fabricated a 50 by 50 by 50 millimeter cube using selective laser sintering, a technique that involves pointing a laser at a specific area predetermined in a computer model to turn powdered SiC into a solid mass.
These three methods helped scientists produce a series of microstructures ranging from 0.5 to 50 millimeters.
The findings have sparked interest in the research community.
“The analysis demonstrates that even though the fabrication of components of complex shapes cannot be accomplished using traditional methods, the microstructures resulting from additive manufacturing are very promising in terms of resistance and suitability for fusion applications,” said Koyanagi, adding that this is important because microstructures are good indicators of performance.
Microstructures will later undergo neutron scattering experiments in the High Flux Isotope Reactor, the highest flux reactor-based source of neutrons for research in the United States. HFIR is a Department of Energy Office of Science user facility at ORNL.
The team is already planning to continue this line of research. Among its future goals is to eventually achieve a relatively pure SiC material for additive manufacturing.
“By matching SiC with these techniques, our material scientists and industry partners can propose new ideas and designs to solve issues that will make the next generation of fusion reactors a reality,” Koyanagi said.
UT-Battelle LLC manages Oak Ridge National Laboratory for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.
