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<p>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-rich <i>α</i><sub>1</sub> rods embedded in a Ni–Al-rich <i>α</i><sub>2</sub> matrix. Magnetic measurements show high saturation magnetization (~&#xa0;120&#xa0;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 refined <i>α</i><sub>1</sub>/<i>α</i><sub>2</sub> features enhance domain wall pinning. Transmission electron microscopy and Lorentz imaging confirm <i>α</i><sub>1</sub>/<i>α</i><sub>2</sub> interfaces 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.</p>

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Processing-Driven Microstructure Control in Additively Manufactured Alnico Permanent Magnets

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年12月29日

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  • A. Duong,
  • I. Smith,
  • O. Bishop,
  • C. Mayer,
  • M. Patel,
  • K. Snyder,
  • E. Carpenter,
  • R. Barua

摘要

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-rich α1 rods embedded in a Ni–Al-rich α2 matrix. 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 refined α1/α2 features enhance domain wall pinning. Transmission electron microscopy and Lorentz imaging confirm α1/α2 interfaces 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.