Suppressing the CeFe2 phase formation and improving the coercivity and thermal stability of Ce-Fe-B alloys by Si substitution

Abstract

Low anisotropy field and low Curie temperature of Ce2Fe14B phase seriously restrict the application of Ce-Fe-B alloys. Most of the previous work suggest that REFe2 phase inevitably forms in the compositions with high Ce content. In this work, Si substitution for Fe is found to not only suppress the formation of CeFe2 phase, but also significantly improve the coercivity Hc and thermal stability of Ce17Fe78-xSixB6 (x = 0–3.0) alloys. All Si-doped alloys exhibit higher Hc and better thermal stability than Ce17Fe78B6 alloy. With increasing Si doping, a relatively high Hc = 525 kA/m is obtained in the Ce17Fe77.75Si0.25B6 alloy. An abnormal increase of Hc as well as almost unchanged Jr and (BH)max is observed in Ce17Fe78-xSixB6 (x > 1.5) alloys. The refined XRD results indicate that the volume fraction of CeFe2 phase can be dramatically reduced via a moderate content of Si doping. Hard magnetic grains are isolated by forming a structure with thin and continuous intermediate layer, consequently preventing the domain wall propagation. The Curie temperature of the main phase monotonically increases from 424 K for x = 0–445 K for x = 3.0, resulting in improved thermal stability. The highest Hc of 530 kA/m, the lowest temperature coefficients (|β| = 0.551%/°C and |α| = 0.368%/°C), and an acceptable Jr = 0.44 T are obtained in Ce17Fe78-xSixB6 (x = 3.0) alloy. The nucleation and pinning are both responsible for the coercivity mechanism of Ce17Fe75Si3B6 alloy, which should be the reason for its high coercivity.