| Sintering studies of the mixture of a coarse 60wt% Sm-Co additive (about 200㎛ size) and a fine SmCo_5 powder (about 5㎛ size) and the mixture of a coarse SmCo_5 powder and a fine additive were made to understand the role of the liquid additive during sintering of the SmCo_5 permanent magnets. The density change of the fine powder mixtures was also studied, varying their total Sm content and sintering time, to understand the sintering of a Sm-rich phase powder of the SmCo_5 homogeneity region. The results showed that the mixture of the SmCo_5 powder and the 60wt% Sm-Co additive was sintered through three stages; 1) Upon melting of the Sm-Co additive, the liquid phase immediately permeated through the SmCo_5 powder during the first stage. 2) As the liquid phase was brought to contact with the SmCo_5 powder, new phases, SmCo₃ and Sm₂Co_7 were formed by interphase reaction and interdiffusion of Sm and Co atoms between the liquid phase and the SmCo_5 powder. On continued sintering, the liquid phase, the SmCo₃ and the Sm₂Co_7 phase disappeared successively in the order of listing, while an equilibrium phase of the powder mixture, that is, a Sm-rich phase of the SmCo_5 homogeneity region was formed during the second stage. 3) During the last stage, solid state sintering of the Sm-rich phase of the SmCo_5 homogeneity region occurred by diffusion of Co-vacancies that were believed to exist in the Sm-rich phase. The experimentally observed relationship between density change of sintered magnets and sintering time was discussed in relation to the theories and experimental results reported previously. |
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