Magnetic and microstructural evolution of Nd-Fe-B processed via HDDR (hydrogenation-disproportionation-desorption-recombination) and Melt-Spinning sintered by SPS (spark plasma sintering)

Abstract

The HDDR (hydrogenation — disproportionation — desorption — recombination) technique and Melt-Spinning have proved to be very effective to obtain Nd 2 Fe 14 B nanocrystalline grains and therefore attaining high values of coercivity. Taking into account the remanence dilution effect found in composite magnets made with nanocrystalline powders, the production of fully-dense magnets with such powders would allow for high remanence and high energy-product magnets. One alternative to consolidate such powders whereas the grain growth could be inhibited is by the spark plasma sintering (SPS) technique. This non-conventional technique has been used for sintering new kinds of ferrous and non ferrous materials, especially to consolidate ultra fine grain, nano-structure and nano-powders. In the SPS process, a pulse delectric current flows through the powder, and then generates local heating at the particle interfaces [1]. Due to its possibility of imposing high heating rates with simultaneous application of pressure, one expects the grain growth to be limited and therefore the high coercivity and remanence could be preserved for the HDDR [2] and Melt-Spinning materials.