Densification of a Nd13Fe78NbCoB7-type sintered magnet by (Nd, Dy)-hydrideadditions using a powder blending technique

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 w ork, 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 m etallurgical route. Increasing the sintering temperature and the duration o f the sintering did not result in any significant improvements in the rho v alues 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 hydr ides on the magnetic properties and microstructural appearance of the sinte red 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 densif ication could be achieved and magnets with densities >7.40 g cm(-3) could b e produced consistently. The total addition of (Nd+Dy), with varying propor tions of Nd and Dy, was limited to 2 at% and at each addition, a full densi ty in the sintered state was attained. Using I at% Nd and 1 at% Dy, an intr insic coercivity (H-ci) of similar to 780 kA m(-1) with a corresponding ene rgy density [(BH)(max)] value of similar to 324 kJ m(-3) were obtained. The se 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 degree s C for I h, followed by air-cooling to room temperature. These studies hav e confirmed that powder blending using Nd and Dy hydrides is a very effecti ve means of promoting liquid phase sintering and optimising magnetic proper ties in Nd-Fe-B-type magnets. (C) 1999 Elsevier Science SIA. All rights res erved.