Hydrogen disproportionation by reactive milling and recombination of Nd2(Fe1−xCox)14B alloys

Abstract Stoichiometric Nd 2 (Fe 1− x Co x ) 14 B alloys ( x =0, 0.25, 0.5, 0.75 and 1) have been disproportionated into NdH 2+δ and bcc–(Fe,Co) (0≤ x ≤0.75) or fcc–Co ( x =1), respectively, by milling in hydrogen at enhanced temperatures. Reactive milling leads to the disproportionation of the thermodynamically very stable Nd 2 Co 14 B alloy. This reaction is not possible via the conventional hydrogenation disproportionation desorption and recombination (HDDR) process. Grain sizes of disproportionated and recombined Nd 2 (Fe,Co) 14 B materials were found to be 2 Co 14 B alloy shows on average slightly smaller grain sizes than the Nd 2 Fe 14 B compound. A more effective exchange coupling leading to enhanced remanences, possibly due to the slightly smaller grain size, has been observed for Nd 2 Co 14 B powders recombined at 600–700°C.