Metastable borides and the inducement of texture in Pr2Fe14B-type magnets produced by HDDR

A modified hydrogenation-disproportionation-desorption-recombination (HDDR) process has been applied to Pr₂(Fe,Co,Zr)₁₄B-type alloys. XRD and Rietveld analysis show that a Fe₃B phase observed in a Pr_13.7Fe_80.3B₆ alloy solid-disproportionated at 875°C is transformed to Fe₂B and bcc Fe on further hydrogen annealing and that the formation of Fe ₃B is partly suppressed when the alloy is processed at 800°C. No residual 2-14-1-type phases are observed after disproportionation of Pr_13.7Fe_63.5Co_16.7Zr_0.1B ₆ alloy but here a new intermediate boride phase, Pr(Fe,Co) ₁₂B₆ (rhombohedral R¯3m), is found. Pr(Fe,Co) ₁₂B₆ transforms to (Fe,Co)₂B and α-(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