Radika of Virginia Commonwealth University

The growing instability in global supply chains for rare-earth elements has heightened the urgency to develop alternative permanent magnets for critical technologies. Alnico alloys offer a rare-earth-free solution with excellent thermal stability and moderate magnetic performance. Their properties arise from a spinodally decomposed microstructure comprising (Fe-Co)-rich ferromagnetic α₁ domains aligned within an (Al-Ni)-rich paramagnetic α₂ matrix. To this end, this work investigates the process–structure–property relationships in Co-free Alnico-3 permanent magnets fabricated using Directed Energy Deposition (DED), a laser-based additive manufacturing technique. Key process parameters—including laser power, scan speed, and powder mass flow rate—are evaluated through the lens of Global Energy Deposition (GED) to assess their influence on microstructural evolution and magnetic behavior.

As-deposited samples exhibit high saturation magnetization (~120 emu/g) and columnar grain growth, with coercivity showing a strong dependence on GED. However, peak magnetic performance is only realized after post-deposition thermal aging, which promotes spinodal decomposition into well-defined α₁/α₂ nanostructures. Lower GED promotes finer α₁ domains and increased α₁/α₂ interfacial density, enhancing coercivity through improved domain wall pinning. In contrast, higher GED leads to microstructural coarsening and a reduction in pinning strength. Lorentz Transmission Electron Microscopy (TEM) reveals the presence of distinct ferromagnetic/paramagnetic phase boundaries acting as dominant pinning sites. Micromagnetic simulations further elucidate magnetization reversal processes and suggest that energy density could be enhanced via interface engineering and potential exchange bias mechanisms. While the theoretical (BH)max of Alnico-3 is ~94 kJ/m³ (~12 MGOe), our findings indicate the feasibility of approaching or exceeding this value through process optimization.

This work establishes a foundational understanding of additive manufacturing–induced microstructure control in Alnico magnets and provides a scalable route for producing rare-earth-free nanocomposite magnets with tunable properties for high-temperature and strategic applications.

Biography:

Radhika Barua is an Assistant Professor in the Department of Mechanical and Nuclear Engineering in the College of Engineering at Virginia Commonwealth University in Richmond, VA. Her research interests are focused on the development of advanced functional magnetic materials and devices for diverse applications in the power and energy sector, including nanocomposite permanent magnets, sensors/actuators for harsh environments, and nanoparticles for biomedical devices. To date, she has authored 50 peer-reviewed research papers, more than 75 international conference papers, and holds 4 current and pending patents. She is also the chair of the IEEE Magnetics Society (Richmond Chapter) and serves as an associate editor for the journals, IEEE Magnetics Transactions and AIP Advances.

Email:

Address:401 W Main Street, Mechanical and Nuclear Engineer, , Richmond, Virginia, United States, 23284