Microstructural studies on Pr-Fe-B-Cu magnets produced by upset forging ofcast ingot

Recent work has shown that Pr-Fe-B-Cu-type permanent magnets have been prod uced from cast ingot materials using upset forging and that intrinsic coerc ivity can be enhanced substantially by a post forging heat treatment at 100 0 degrees C for 5 h plus 500 degrees C for 3 h. In the present work, the mi crostructures of both as-upset forged and heat treated magnets have been in vestigated by optical and by scanning electron microscopy (SEM) in an attem pt to er,plain the origin of this increase in the intrinsic coercivity. Bac kscattered electron images on the SEM, energy dispersive X-ray analysis (ED X) and thermomagnetic analysis confirm the presence of Pr2Fe17 (Fe/Pr appro ximate to 8.2) after the upset forging process and heat treatment at 1000 d egrees C. The quantity of this phase is substantially reduced after the sec ond heat treatment at 500 degrees C. In addition a Pr34Fe62Cu4 (Pr6Fe13Cu) phase has also been observed by SEM and EDX analysis after the anneal at 50 0 degrees C. The increase in the coercivity on annealing has been attribute d to the grain boundary improvement isolation and to the reduction in the a mount of the Pr2Fe17 phase after heat treatment at 500 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.