Effects of heat treatments on coercivity and microstructure in Nd15Fe77B8 sintered magnets

The effects of post-sintering heat treatments on the structure and properties in sintered Nd15Fe77B8 magnets have been investigated. In the as-sintered sample, the crystal structure of the Nd-rich phase was f.c.c., while the Nd-rich phase transformed into a superlattice after heat treatment at 600°C for 1 h. However, the structures of Nd2Fe14B and B-rich (Nd1+ϵFe4B4) phases did not change upon heat treatment. It is suggested that the formation of the superlattice enhances the coercivity of the magnets.