Abstract
This work has shown that heating Nd 16Fe 76B 8-type materials in a hydrogen atmosphere, with subsequent vacuum annealing at greater than 750°C produces coercive powders which are suitable for the production of polymer-bonded magnets. A study of the material at different stages of the process has confirmed that the Nd-Fe-B alloy disproportionates into iron, Fe 2B and neodymium hydride before recombining during the vacuum annealing stage to produce the fine-grained microstructure necessary for highly coercive material. The grain size of the final microstructure has been found to be very dependent on the temperature at which the hydrogenation-disproportionation-desorption cycle is carried out with optimum properties for the Nd 16Fe 76B 8 alloy being obtained for a desorption temperature of 785°C for 1 h.
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