A study on the Nd-rich phase evolution in the Nd-Fe-B sintered magnet and its mechanism during post-sintering annealing

► No Nd-rich grain boundary phase from the Dy segregated Nd-rich phase. ► Formation of the Dy segregated Nd-rich phase should be reduced for the Dy saving. ► Cu-enriched C-Nd2O3 triple junction and grain boundary phases are formed during the 2nd post-sintering annealing. ► Cu-segregation stabilized the meta-stable C-Nd2O3 by rearrangement of the Nd atoms in the h-Nd2O3. ► C-Nd2O3 phase reduces the lattice misfit with the main phase, dramatically.