The role of cobalt addition in magnetic and mechanical properties of high intrinsic coercivity Nd-Fe-B magnets

The role of cobalt addition in magnetic and mechanical properties of high intrinsic coercivity Nd-Fe-B magnets by adding cobalt element and blending micron cobalt powder was investigated. The results showed that the excellent magnetic properties of high intrinsic coercivity Nd-Fe-B magnets were obtained at the Co content of 1.5 wt%, and then the intrinsic coercivity and fracture toughness decline after blending 3 wt% micron Co powder. Blending Co powder increased the Co content of main phase grain and Nd-rich phase, and the phenomenon that the Co powder additive is in the presence of pure Co particles was not been found in the sample. Simultaneously, blending Co powder reduced the heavy rare earth content of main phase grain, and new phases containing heavy rare earth and Co were formed, such as soft ferromagnetic phase R(FeCo)3, the low-anisotropy phase R(FeCo)5 and rich-B phase R1.1(FeCo)4B4. These phenomena lead to a decrease in the intrinsic coercivity of high intrinsic coercivity Nd-Fe-B magnets. Further investigation on the grain and grain boundary indicated that the effect mechanism of blending Co powder on magnetic properties is not the same as that of the traditional alloying route.