This work reports improvements in the density (rho) and permanent magnetic properties of sintered magnets made from a Nd13Fe78NbCoB7-type alloy, as a result of additions of Nd-, Dy- or (Nd+Dy)-powder in the form of hydrides, using; a powder blending technique. Under the conditions employed in this work, it proved impossible to achieve a full density in the sintered magnets, processed from this alloy in the cast state, using a standard HD-powder metallurgical route. Increasing the sintering temperature and the duration of the sintering did not result in any significant improvements in the rho values and the highest possible density achieved in the sintered magnets was only 7.05 g cm(-3). In an attempt to improve these densities, the effects of powder blending Nd and Dy additions in the form of their respective hydrides on the magnetic properties and microstructural appearance of the sintered magnets have been studied. Using the same processing conditions, it was found that, by an addition of only 2 at% Nd or Dy, practically full densification could be achieved and magnets with densities >7.40 g cm(-3) could be produced consistently. The total addition of (Nd+Dy), with varying proportions of Nd and Dy, was limited to 2 at% and at each addition, a full density in the sintered state was attained. Using I at% Nd and 1 at% Dy, an intrinsic coercivity (H-ci) of similar to 780 kA m(-1) with a corresponding energy density [(BH)(max)] value of similar to 324 kJ m(-3) were obtained. These values were improved to similar to 950 kA m(-1) and similar to 331 kJ m(-3), respectively, by applying a standard annealing treatment of 600 degrees C for I h, followed by air-cooling to room temperature. These studies have confirmed that powder blending using Nd and Dy hydrides is a very effective means of promoting liquid phase sintering and optimising magnetic properties in Nd-Fe-B-type magnets. (C) 1999 Elsevier Science SIA. All rights reserved.
