On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

Journal Article · Thu Apr 26 00:00:00 UTC 2018 · Acta Materialia

DOI: https://doi.org/10.1016/j.actamat.2018.04.042 · OSTI ID:1454574

Zhou, Lin ^[1]; Guo, Wei ^[2]; Poplawsky, J. D. ^[2]; Ke, Liqin ^[1]; Tang, Wei ^[1]; Anderson, I. E. ^[1]; Kramer, M. J. ^[1]

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1. Ames Lab., Ames, IA (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Here, alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2-fold increase of intrinsic coercivity (H_ci) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (α₁) isolation, development of Cu-rich spheres/rods/blades and additional α₁ rod precipitation that occurs during the MA and draw, likely play a key role in Hci enhancement. Chemical ordering of the Al-Ni-phase (α₂) and formation of Ni-rich (α₃) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC02-07CH11358; AC05-00OR22725
• OSTI ID: 1454574
• Report Number(s): IS-J--9646; PII: S1359645418303197
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: C Vol. 153; ISSN 1359-6454
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English