Effects of Ti and (or) Cu on microstructures and magnetic properties of sintered Nd-Fe-B magnets

The alloying elements Ti and(or) Cu were added into the intergranular regions of sintered Nd-Fe-B magnets and their effects on microstructures and magnetic properties of the magnets were investigated. The results showed that a small amount of Ti and(or) Cu additions can enhance the coercivity and have little effect on the remanence of Nd-Fe-B magnets. Compared with individual addition of pure Ti or Cu elements, Ti and Cu co-addition of intergranular region is more efficient to improve the coercivity of the magnets. The improvement of the coercivity can be attributed to the segregation of Cu element on the surface of the magnetic phase (Nd₂Fe₁₄B) and the occurrence of fine Nd-Fe-Ti particles near grain boundaries. The former can prevent the magnetic coupling of Nd₂Fe₁₄B grains to a certain degree and impede effectively the propagation of reversed domain walls through the magnetic phase grains. The latter can inhibit the growth of magnetic phase grains during the sintering process, resulting in a finer grain size. Both are beneficial to the coercivity enhancement. With increasing Ti content above 0.8%, a strip Ti-rich phase appears in the intergranular region, resulting in the dramatic reduction of the remanence of Nd-Fe-B magnets.