Printing a sustainable future: Additive manufacturing reduces waste and improves supply chain resilience for magnet production
Radhika Barua, Ph.D., mechanical and nuclear engineering assistant professor, is paving the way to a sustainable future. Her research will transform magnet manufacturing, replacing the costly, energy-intensive processes for producing traditional rare-earth magnets. Through additive manufacturing — commonly known as 3D printing — Barua will create high-performance magnets for consumer and industrial electronics applications. With research focused on reducing production costs, minimizing energy consumption and limiting environmental impact, the application of her work also extends to renewable energy technologies like wind turbines and electric vehicles.
Lasers that “print” nanocomposite alloys
Using concentrated heat from a laser to melt metal, Barua’s research employs a form of additive manufacturing called direct energy deposition (DED). Material “printed” by DED can be shaped into complex geometries in a molten state, perfect for creating precise, customized components. Directed energy deposition processes generate and manage high thermal energy, which can heat materials to temperatures well above their melting points. Depending on the alloy processed, temperatures often exceed 1000°C. The cooling rates achieved with DED are crucial for microstructure formation and can vary between 1000 – 100,000 Celsius per second based on the scan strategy (the pattern and sequence by which metal alloy is printed), power settings and material properties.
“Typical 3D printing cares about creating unique geometries,” says Barua. “But the goal of this research doesn’t always involve a material’s overall shape. The performance of a magnet depends heavily on what happens at the microscopic level, specifically through two key features: grain boundaries and magnetic domains. This is especially important in cutting-edge materials like nanocomposite permanent magnets.”
Nanocomposite magnets consist of nanoscale grains, each measuring only a few billionths of a meter in size and exhibiting distinct magnetic properties. The interfaces between these grains, known as grain boundaries, play a pivotal role in determining the magnet’s overall strength and efficiency. Properly aligned grain boundaries facilitate the smooth flow of magnetic forces and minimize energy losses. In contrast, poorly arranged boundaries obstruct magnetic alignment, significantly diminishing the magnet’s performance.
Magnetic characteristics of each grain are governed by its magnetic domain, clusters of atoms with magnetic fields aligned in the same direction. These domains can be thought of as miniature magnets working in unison. The more uniformly aligned the domains are across grains, the stronger and more cohesive the overall magnet becomes. Achieving this alignment, however, is incredibly challenging in nanocomposite magnets because their composition includes many different materials. This makes aligning magnetic domains uniformly across all grains difficult due to the material’s complexity.
Barua’s research using DED carefully controls the formation of grains and how their boundaries interact. By printing nanocomposite magnets layer by layer, her team seeks to optimize the microstructure and ensure magnetic domains are aligned for maximum performance.
Nanocomposite alternatives to rare-earth magnets
Rare-earth magnets, which Barua hopes to replace, have exceptional magnetic strength and stability. Their crystalline structures exhibit magnetocrystalline anisotropy (pronounced an-ahy-so-truh-pee), the property of a ferromagnetic material where it takes more energy to magnetize it one direction over another direction. This property enables a rare-earth magnet’s ability to remain magnetic after the magnetization process.
Without magnetocrystalline anisotropy, rare-earth-free nanocomposite magnets use their fine microstructure to enhance magnetic properties. This is achieved at the nanoscale by using DED to combine various 3d transition elements (the “d” here refers to the shape of the d orbitals in an atom’s electron configuration) from the periodic table, like iron, copper and manganese.
Molten material cools quickly once it is printed in DED. Rapidly solidified alloys demonstrate unique structural properties that lead to a fine microstructure, resulting in smaller grain sizes and a more uniform distribution of phases. In this instance, a phase is the name given to chemically uniform and physically distinct regions of material like the different elements an alloy is composed of.
These features can enhance physical properties, such as increased strength and toughness. Additionally, the rapid cooling prevents formation of equilibrium phases that limit the performance of magnetic materials. Non-equilibrium structures formed by rapid cooling tend to have stronger magnetic anisotropy and fine-grained structures.
“There are other forms of anisotropy we can use to replace the magnetocrystalline anisotropy found in rare-earth magnets,” says Barua. “We’re focusing on shape anisotropy, exchange bias anisotropy and domain wall pinning in this research.”
Shape anisotropy
Magnetic materials can tend toward a specific orientation based on shape. If particles are arranged in needle-like forms, the magnetic forces within that needle will prefer to align along the longest axis. This is shape anisotropy.
Exchange bias anisotropy
When the 3d transition element composite includes ferromagnetic and antiferromagnetic phases, researchers can harness exchange bias anisotropy. By layering an easy-to-magnetize ferromagnetic material with an antiferromagnetic material, the resultant composite becomes easier to magnetize in a specific direction, creating a bias to that direction at the interphase boundary between the two layers. The result is a permanent magnet that can store and deliver more energy while remaining magnetized at high temperatures.
Domain wall pinning
Just like grain boundaries represent the physical space where two grains meet, the domain wall is a boundary between two magnetic domains. When domain walls can move freely, the shift in the magnetic moments of the domains can result in a loss of magnetic properties, especially under external magnetic fields or temperature changes.
Domain wall pinning hinders the movement of domain walls and is achieved by introducing structural defects or impurities into the material. These defects act as obstacles, trapping the domain walls and preventing them from moving easily. This resistance creates a situation where material can magnetize more effectively and hold onto that magnetism longer. The process is called domain wall pinning.
Tuning the microstructure with computer modeling
The chemically uniform and physically distinct material in a nanocomposite alloy that influences its magnetic properties is called the primary matrix phase. Within the same material, secondary phase particles are additional materials that modify behavior of the primary phase.
Achieving the optimal size, shape and distribution of secondary phase particles is crucial for enhancing magnetic properties. To this end, Barua collaborates with Jayasimha Atulasimha, Ph.D., Engineering Foundation Professor in the Department of Mechanical and Nuclear Engineering, to conduct micromagnetic simulations. These simulations model and predict the effects of different particle characteristics on the overall magnet behavior, facilitating the design of advanced nanocomposite magnets with improved performance.
“The particles of the secondary phase have to be just right,” says Barua. “If they’re too small, you lose the exchange anisotropy and the particles start interacting with each other. So there’s a relationship where they have to be spaced apart relative to their size to prevent this. Dr. Atulasimha models these conditions for us and gives us an estimated size and distribution. We use his simulations as guidelines to create the material and share our results with him, adjusting his simulations before manufacturing the next batch of material.”
Putting it all together
The Commonwealth Center for Advanced Manufacturing (CCAM) is a key location for Barua’s additive manufacturing research. Printers used in the DED process are housed at CCAM, and the consortium of academic and industry professionals who collaborate there creates a unique learning environment. Researchers like Barua can fund graduate students through CCAM and provide them with needed hands-on and experiential learning opportunities. It is a unique model for workforce development, where industry aids research and students learn skills that allow them to make significant contributions to companies that hire them immediately. The Commonwealth Center for Advanced Manufacturing is a good opportunity for students to understand how industry works and what the needs of industry are.
At CCAM, Barua’s team has made significant enhancements to the DED machine, like integrating a permanent magnet Halbach array beneath the base print layer to improve overall fabrication efficiency. Employing this magnetic field below the base print layer overcomes an inherent shortcoming of powder-fed DED systems. During printing, the metal powder is sprayed into the laser where it is heated and melts. Because it is a spray, not all of the powder lands where it needs to. The measurement of how much powder lands in the appropriate area is called catchment efficiency. Through the magnetic fields of a Halbach array, the metal powder streams, which respond to magnetism, can be focused to improve catchment efficiency. This reduces material waste and allows the DED system to be more precise, consuming less energy.
“You can control how big or how small the grains are by controlling the print speed, the mass at which the material is flowing out of the hopper and by controlling the laser power,” says Barua. “In addition to the magnetic field, the DED machine we use at CCAM has many sensors and scopes. There’s an optical camera, a thermal camera, a distance meter, an infrared camera and more. That means you can see the melt being made and how it’s solidifying in real time. That helps during the verification process of the experiment in real time.”
With an undergraduate degree in chemical engineering, Barua came to the United States from India to pursue a career in chemical engineering. She switched to material science during her Ph.D. while working with her advisor in the Nanomagnetism Research Group at Northeastern University in Boston.
“My Ph.D. was funded by the Basic Energy Sciences program in the U.S. Department of Energy. Much of my research supports fundamental studies to understand, predict and control matter and energy at the electronic, atomic and molecular levels,” says Barua. “When I came to VCU, it was because the College of Engineering possessed state-of-the-art research equipment I needed for my research. For example, the Nanomaterials Core Characterization Facility (NCC) has a suite of scanning electron microscopy tools. Having these resources is a big help to researchers and to students wanting to learn advanced techniques that can advance their careers.”
Barua regularly collaborates with Carl Mayer, Ph.D., a scientist at the NCC and Everett Carpenter, Ph.D., professor in the VCU Department of Chemistry and Co-Director of the Nanoscience and Nanotechnology Program. Her work has received funding from the National Science Foundation and VCU Breakthroughs Fund for work in material science and how it can impact sustainability by reducing the harmful environmental impact of manufacturing rare-earth magnets.
The Department of Mechanical and Nuclear Engineering provides undergraduate and graduate students with the opportunity to perform real-world research as soon as they enroll. From applying material science to additive manufacturing techniques to optimizing coolant systems for nuclear reactors and more, students gain understanding of many important engineering topics. Browse videos and recent news from the Department of Mechanical and Nuclear Engineering to discover how the College of Engineering at Virginia Commonwealth University prepares the next generation of scientists and engineers for the challenges of the future.
Categories Mechanical & Nuclear Engineering