Challenges in the further development of powder processed rare earth-iron-boron magnets - Hywell Davies, University of Sheffield, UK

Neodymium-Iron-Boron-based alloy hard magnets have major and extremely diverse technological applications, including permanent magnet motors such as drives for electric and hybrid vehicles, voice coil motors for computer hardware, spindle and stepper motors, magnetic bearings and couplings, actuators, biomedical devices, consumer and office electronic devices such as CD and DVD players, digital cameras, watches, clocks and timer switches and in consumer electrics. These magnets are produced by various powder processing routes. The so-called liquid phase sintering route has been progressively developed to yield combinations of very high coercivity and magnetic energy density, based on anisotropic magnets, but at relatively high cost. The melt spinning route has, in contrast, been successfully exploited to yield less reactive alloy powder which can be compression or injection moulded into less costly polymer bonded magnets but having lower maximum energy densities.

There is a pressing need, however, to reduce the concentration of very scarce rare earth additives, notably Dysprosium, in the sintered magnets, which are added to enhance their coercivity, especially for electric/hybrid vehicle applications, since the volume of magnets employed is relatively very large and the world’s total supply of this element is projected to be insufficient to sustain its use in the longer term. Improving the  corrosion/oxidation resistance of sintered magnets and improving the recyclability of the rare earth constituents are also significant issues. For bonded magnets, there is a need to improve the processability of the ribbon precursor for the powder in order to be able to exploit, on a practical scale, the enhancement in maximum energy density that has been demonstrated to be associated with a nanocomposite hard/soft structure. These and other issues will be discussed in the context of improved material conservation and reductions in total energy consumption, with emphasis on applications in transport.