Regensburg 2016 – scientific programme

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MA: Fachverband Magnetismus

MA 17: Poster Session I

MA 17.82: Poster

Tuesday, March 8, 2016, 09:30–12:30, Poster B1

Coercivity Enhancement of Nd-Fe-B Permanent Magnets by Grain Boundary Diffusion — •Konrad Loewe, Tim Lienig, Dimitri Benke, and Oliver Gutfleisch — TU Darmstadt, FB Materials Science, 64287 Darmstadt

A way to enhance the relatively poor temperature stability of coercivity of modern Nd-Fe-B-based sintered magnets is the substitution of Heavy Rare Earth (HRE) for Nd in the so-called '2-14-1'-structure of the magnetic main phase. This way the anisotropy field Ha increases, albeit at the expense of the saturation magnetization Ms and therefore the maximum storable energy. A possibility to overcome this drawback is to concentrate the HRE only at the features of the microstructure where demagnetization is starting (so-called 'weak links'), i.e. the grain boundaries. In technical practice, the HRE are deposited on the surface of the finished magnets and diffuse into the volume during a heat treatment.

In the present work, it is shown that the diffusion of HRE mainly occurs over the grain boundaries leading to a distinct two phase microstructure consisting of HRE-lean grain cores surrounded by HRE-rich grain boundary areas. On the macroscopic scale the so obtained coercivity enhancement is decreasing with diffusion distance, leading to magnets with gradient properties over the range of several mm. The geometry dependent optimum distribution of coercivity is predicted with FEM simulations and correlated with experimental data.