The use of metal hydride powder blending in the production of NdFeB-type magnets

The ability to vary the composition of NdFeB-type magnets, during or after the milling stage offers a number of advantages. To this end, powder blendi ng processes have been det eloped. In the present work. the sintering chara cteristics of a Nd13Fe80.5B6.5 alloy have been improved by powder blending with neodymium hydride, A blending addition of 1 at% of neodymium in the fo rm of Nd-hydride, consistent with a final composition of Nd14Fe79.6B6.4, wa s sufficient to reduce the required sintering temperature from 1130 to 1070 degreesC, with a resultant improvement in the coercivity due to less grain growth and better grain isolation. The addition of dysprosium hydride to a Nd14Fe79B7 alloy by blending resulted in a further enhancement of the coer civity, a 2 at% addition yielding an approximate doubling in the value of i ntrinsic coercivity. Examination of the microstructure of dysprosium-hydrid e blended magnets showed the dysprosium to be concentrated in the outer reg ions of the matrix grains, with the centres being essentially dysprosium-fr ee. Hydrogen has also been employed in improving the milling characteristic s of the high melting point elements niobium and vanadium. Fine powders of niobium and vanadium hydride were prepared acid were successfully blended i nto magnets with an even distribution throughout the microstructure. These studies have shown that powder blending of metal hydrides is an effective w ay of both promoting liquid-phase sintering in low rare earth composition m agnets and of modifying the grain boundary phases and hence the magnetic pr operties. (C) 2001 international Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.