A study of the effects of Cu-addition on the annealing behavior and microstructures of Nd-Fe-B type sintered magnets

A high temperature homogenization treatment (1100°C for one hour) is applied to sintered magnets of Nd₁₇Fe_76.5B₅Cu_1.5. This is followed by a low temperature anneal (600°C for one hour). The magnetic properties of the samples are related to their microstructure. The formation of Nd₂Fe₁₇ during the homogenization and quench treatment is thought to be responsible for the fall in coercivity, and the increased remanence is attributed to an increased fraction of the Nd₂Fe₁₄B matrix phase. The subsequent anneal at 600°C causes the disappearance of most of the Nd₂Fe₁₇ phase and this corresponds with an increase in the coercivity. Quenching after the 600°C anneal gives better magnetic properties than slow cooling from this temperature. Furnace cooling the sample after homogenization results in the disappearance of the Nd₂Fe₁₇ phase and this treatment gives the highest coercivity and energy product