Sm-Fe-N alloys prepared by Si-doping-assisted strip casting without prolonged high-temperature annealing

Novel preparation methods free of prolonged high temperature annealing (PHTA) are highly desirable for fabricating high-performance anisotropic Sm-Fe-N powders. In this study, a Si-dope-assisted strip casting method was designed in preparing Sm 2 Fe 17- x Si x N 3-δ ( x = 0-1.0) material, and high-performance Sm-Fe-N powder with optimal maximum energy product up to 27.8 MGOe were demonstrated free of PHTA at x = 0.2. Systematic investigations were conducted into the effects of Si doping on the microstructural evolution and magnetic changes. The optimal maximum energy product is approximate 15% enhancement relative to the that of x = 0. The performance enhancement stems from not only the absence of α-Fe secondary phase but also the simultaneous suppression of Sm-rich secondary phase in Sm 2 Fe 17 -based alloys. A nitridation-induced disappearance of Sm-rich secondary phase was observed during the nitriding process. The doped Si exhibits complex distribution in prepared alloys, with higher atomic ratios at the grain boundaries than in the crystals of the main phase. When the doping amount reaches x ≥ 0.5, all magnetic properties deteriorate owing to the impeded nitridation of the main phase. Both the micrometer-sized α-Fe phase inherited from the as-cast Sm 2 Fe 17 alloys and the α-Fe phase derived from Sm-rich-phase decomposition are found decoupled from the Sm 2 Fe 17 N 3-δ main phase, exerting only a slight deteriorating effect on the coercivity of the Sm-Fe-N powders.