Events

Seminar of International Laboratory of High Magnetic Fields and Low Temperatures PAS

Multiscale Characterisation and Modelling of Nd-Fe-B Permanent Magnets

dr Thomas G. Woodcock

Leibniz Institute For Solid State and Materials Research - IFW Dresden, Germany

Nd-Fe-B permanent magnets are currently used in hybrid electric vehicles and direct-drive wind turbines. They must operate at elevated temperature (150-200°C) and therefore high coercivity magnet grades, in which Nd is partially substituted by Dy, are typically required. The disadvantage of this approach is the reduction of remanent magnetisation by antiferromagnetic coupling of Dy and Fe while usage of heavy rare earth elements in a strongly growing market is unsustainable. In order to reduce the Dy content or replace Dy entirely while maintaining the high temperature performance, a greater fundamental understanding of the physical mechanisms controlling the coercivity of the magnets is required. The distribution and character of secondary phases in the microstructure are critical for the coercivity. These secondary phases are 1 nm thick intergranular films and 2-3 µm large grains. High quality characterisation and modelling on multiple length scales are therefore required. Aberration-corrected scanning transmission electron microscopy (STEM), combined with electron energy loss spectroscopy (EELS) has been used to study interfaces in Nd-Fe-B magnets on the atomic scale. Electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDX) have yielded the crystal structure, orientation, chemical composition and spatial distribution of the secondary phases on the micron scale. The use of these techniques to provide input parameters for atomistic models of interfaces and finite element models of grain ensembles will also be discussed in detail.