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arXiv · 1906.07388

Effect of grain-boundary diffusion process on the geometry of the grain microstructure of Nd$-$Fe$-$B nanocrystalline magnets

Ivan Titov·Massimiliano Barbieri·Philipp Bender·Inma Peral·Joachim Kohlbrecher·Kotaro Saito·Vitaliy Pipich·Masao Yano·Andreas Michels
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Abstract

Hot-deformed anisotropic Nd$-$Fe$-$B nanocrystalline magnets have been subjected to the grain-boundary diffusion process (GBDP) using a $\mathrm{Pr}_{70}\mathrm{Cu}_{30}$ eutectic alloy. The resulting grain microstructure, consisting of shape-anisotropic Nd$-$Fe$-$B nanocrystals surrounded by a Pr$-$Cu-rich intergranular grain-boundary phase, has been investigated using unpolarized small-angle neutron scattering (SANS) and very small-angle neutron scattering (VSANS). The neutron data have been analyzed using the generalized Guinier-Porod model and by computing model-independently the distance distribution function. We find that the GBDP results in a change of the geometry of the scattering particles:~In the small-$q$ regime the scattering from the as-prepared sample exhibits a slope of about $2$, which is characteristic for the scattering from two-dimensional platelet-shaped objects, while the GBDP sample manifests a slope of about $1$, which is the scattering signature of one-dimensional elongated objects. The evolution of the Porod exponent indicates the smoothing of the grain surfaces due to the GBDP, which is accompanied by an increase of the coercivity.

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Ivan Titov, Massimiliano Barbieri, Philipp Bender, Inma Peral, Joachim Kohlbrecher, Kotaro Saito, Vitaliy Pipich, Masao Yano, Andreas Michels. 2019-06-18. Effect of grain-boundary diffusion process on the geometry of the grain microstructure of Nd$-$Fe$-$B nanocrystalline magnets. https://doi.org/10.1103/physrevmaterials.3.084410

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