Coercivity enhancement and microstructural characterization of Sm2Fe17Nx alloys prepared by mechanochemical treatment

This paper reports that high coercivity Sm2Fe17Nx alloy of fine grain size was successfully synthesized by a modified mechanochemical treatment from Sm11.83Fe88.17 cast alloy. The effects of the Ca-added mechanical milling and the following heat treatments on the characteristics of the alloy samples were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and vibrating sample magnetometer. The results indicate that, after a 6 h milling of the mixture of hydrogen decrepitated Sm–Fe powders and Ca granule, general tendency for the as-milled powders was not only to discompose into amorphous α-Fe and Sm–Fe phase, but also to disproportionate into SmHx and α-Fe phase gradually, and the oxidization of Sm was barely detectable while CaO phase appeared. A subsequent reduction–diffusion at 900 °C for 1 h and nitrogenation at 450 °C for 4 h resulted in the formation of Sm2Fe17Nx without obvious α-Fe phase and Sm oxide after a washing treatment. The magnetic measurements showed that the coercivity of more than 16 kOe was obtained for the mechanochemically synthesized sample, while its squareness of the demagnetization curve was much improved, compared with the samples without Ca-added mechanical milling or reduction–diffusion treatment, due to its high purity and mean grain size found to be approximately 40–65 nm.