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This work reports the first demonstration of in situ magnetic-field-assisted Directed Energy Deposition (DED) for fabricating phase-separated Alnico permanent magnets. A custom Halbach array of N52 NdFeB magnets generated an in-plane magnetic flux density of ∼1250 G during deposition, influencing melt-pool convection and solidification. Using optimized DED parameters (1000 W laser power, 450 mm/s scan speed, 300 μm layer thickness), both cuboid and ring-shaped geometries were produced. Field-assisted cuboids exhibited distinct dogbone morphologies attributed to magnetohydrodynamic flow, while ring geometries showed enhanced dimensional uniformity and improved phase homogeneity. X-ray diffraction confirmed suppression of spinodal decomposition in the as-processed state and formation of α1 (Fe–Co–rich) and α2 (Ni–Al–rich) phases after heat treatment. Magnetometry revealed improved coercivity and magnetic anisotropy in field-assisted samples, achieving an energy product of (BH)max = 0.53 MGOe. These findings establish magnetic-field-assisted DED as a scalable pathway for engineering the microstructure of nanocomposite magnetic materials.
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This content will become publicly available on February 1, 2027
Processing-Driven Microstructure Control in Additively Manufactured Alnico Permanent Magnets
Abstract This work investigates the process–structure–property relationships in cobalt-free Alnico-3 permanent magnets fabricated using directed energy deposition (DED), a laser-based additive manufacturing technique. Systematic variation of laser power, scan speed, and powder mass flow rate is considered through the framework of global energy deposition (GED), a derived parameter that consolidates energy input across operating conditions. Microstructural characterization reveals that as-deposited samples develop columnar grains whose size increases with GED, while heat treatment drives spinodal decomposition into the functional two-phase microstructure comprising ferromagnetic Fe-richα1rods embedded in a Ni–Al-richα2matrix. Magnetic measurements show high saturation magnetization (~ 120 emu/g) in all states, with measurable coercivity in the as-processed condition that increases with GED. However, maximum coercivity and remanence are achieved only after post-deposition aging, particularly under lower GED, where refinedα1/α2features enhance domain wall pinning. Transmission electron microscopy and Lorentz imaging confirmα1/α2interfaces as active pinning sites, directly linking nanoscale phase morphology to magnetic response. Collectively, these results demonstrate the pivotal role of thermal history in tailoring phase separation and establish DED, guided by GED-based process optimization, as a promising pathway for manufacturing high-performance, sustainable, rare-earth, and cobalt-free permanent magnets.
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- Award ID(s):
- 2310234
- PAR ID:
- 10710132
- Publisher / Repository:
- JOM
- Date Published:
- Journal Name:
- JOM
- Volume:
- 78
- Issue:
- 2
- ISSN:
- 1047-4838
- Page Range / eLocation ID:
- 1965 to 1975
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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