Hydrogenation disproportionation desorption recombination in Sm–Co alloys by means of reactive milling

Abstract

Sm–Co-type alloys were disproportionated by milling in hydrogen at enhanced temperatures. X-ray diffraction confirmed the disproportionation of the SmCo5 and Sm2Co17 phases into Sm hydride and α-Co. This “reactive milling” procedure facilitates the disproportionation of these alloys which are characterized by a very high thermodynamic stability, and therefore are not available for a standard hydrogenation disproportionation desorption recombination treatment. Recombination of the reactively milled powders leads to the formation of the original phases, now with dramatically refined grain sizes of around 25 nm and significant coercivities such as μ0JHC=3.7 T in the case of the SmCo5 alloy. Exchange coupling between the nanoscaled grains resulted in magnetically single phase behavior despite a multiphase microstructure. In particular, for the Sm2Co17 alloy, a remanence enhancement was observed for recombination temperatures ⩽700 °C.