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arXiv · 1810.12580

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

Lin Zhou·Wei Guo·Jonathan D. Poplawsky·Liqin Ke·Wei Tang·Iver E. Anderson·Matthew J. Kramer
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Abstract

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 ($H_\text{ci}$) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase ($\alpha_1$) isolation, development of Cu-rich spheres/rods/blades and additional $\alpha_1$ rod precipitation that occurs during the MA and draw, likely play a key role in $H_\text{ci}$ enhancement. Chemical ordering of the Al-Ni-phase ($\alpha_2$) and formation of Ni-rich ($\alpha_3$) 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.

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Lin Zhou, Wei Guo, Jonathan D. Poplawsky, Liqin Ke, Wei Tang, Iver E. Anderson, Matthew J. Kramer. 2018-10-30. On spinodal decomposition in alnico---a transmission electron microscopy and atom probe tomography study. https://doi.org/10.1016/j.actamat.2018.04.042

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