Corrosion behavior of NdFeB permanent magnets

(Korrosionsverhalten von NdFeB Magneten)

The microstructure of NdFeB magnets usually comprising ferromagnetic grains surrounded by intergranular Nd-rich phase regions is critical for their corrosion stability. We have fundamentally studied the effect of various materials parameters, e.g. composition including additives, grain size and texture, on the complex corrosion processes of magnet materials in different electrolytes. Corrosion degradation is driven not only by the active dissolution tendency of Nd-rich phases but also by the strong hydrogen absorption capability of the material. In particular, it was demonstrated that the magnetization state of the magnet material is decisive for their corrosion rates. Base studies on Fe revealed that magnetic field gradient forces determine the (local) corrosion activity of ferromagnetic electrodes. Accelerated corrosion was also confirmed for (coated) magnets that were subjected to specific tests conditions which are relevant for e-motor applications.   

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Mater. Corros. 66 (2015) 152.

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Mater. Corros. 65 (2014) 891

R. Sueptitz et al., Effect of magnetization state on the corrosion behaviour of NdFeB permanent magnets,
Corros. Sci.  53 (2011) 2843

R. Sueptitz, Impact of magnetic field gradients on the free corrosion of iron,
Electrochim. Acta 55 (2010) 5200.

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Journal of Alloys and Compounds 415 (2006) 111