Metastable borides and the inducement of texture in Pr/sub 2/Fe/sub 14/B-type magnets produced by HDDR

Abstract

A modified hydrogenation-disproportionation-desorption-recombination (HDDR) process has been applied to Pr/sub 2/(Fe,Co,Zr)/sub 14/B-type alloys. XRD and Rietveld analysis show that a Fe/sub 3/B phase observed in a Pr/sub 13.7/Fe/sub 80.3/B/sub 6/ alloy solid-disproportionated at 875/spl deg/C is transformed to Fe/sub 2/B and bcc Fe on further hydrogen annealing and that the formation of Fe/sub 3/B is partly suppressed when the alloy is processed at 800/spl deg/C. No residual 2-14-1-type phases are observed after disproportionation of Pr/sub 13.7/Fe/sub 63.5/Co/sub 16.7/Zr/sub 0.1/B/sub 6/ alloy but here a new intermediate boride phase, Pr(Fe,Co)/sub 12/B/sub 6/ (rhombohedral R~3m), is found. Pr(Fe,Co)/sub 12/B/sub 6/ transforms to (Fe,Co)/sub 2/B and /spl alpha/-(Fe,Co) on further hydrogen annealing or conventional disproportionation. For both alloys it is found that processing at higher temperature leads to a better texture on recombination. The role of the Co and Zr additives is not primarily the stabilization of the 2-14-1 matrix phase against hydrogen disproportionation but more importantly the stabilization of intermediate boride phases.