The influence on sintering of the $SmCo_5$ permanent magnets of a liquid phase formed by melting of Sm-Co additive containing 60wt% Sm was investigated in relation to liquid phase sintering. Model-sintering studies of the mixture of a coarse (about 200um size) Sm-Co additive and a fine (about 5um size) $SmCo_5$ powder and the mixture of a coarse (about 200um size) $AmCo_5$ powder and a fine (about 5um size) Sm-Co additive were made to understand the influence on sintering of the $SmCo_5$ permanent magnets of a liquid phase Sm-Co additive.
Upon melting of the Sm-Co additive, the liquid phase immediately permeated through capillaries between fine $SmCo_5$ powder particles. As the liquid phase was brought to contact with the $SmCo_5$ powder, new phases $SmCo_5$ and $Sm_2Co_7$ were formed by interphase reaction and interdiffusion of Sm and Co atoms between the liquid phase and the $SmCo_5$ powders. On continued sintering, the liquid phase, the $SmCo_3$ phase and the $Sm_2Co_7$ phase disappeared successively in the order of listing, while an equilibrium phase of the powder mixture, a Sm-rich phase of the $SmCo_5$ homogeneity region was formed. It is believed that the liquid phase formed by melting of the Sm-Co additive plays and essential role in converting the composition of the powder mixture to that of an equilibrium Sm-rich phase of the $SmCo_5$ homogeneity region.
The shrinkage of the powder mixtures was studied, varying their total Sm contents in the range between 35 and 38wt%. The powder mixture whose equilibrium phase was the Smrich phase of the $SmCo_5$ homogeneity region exhibited the maximum shrinkage. This is attributed to the fact that Co-vacancy concentration is the maximum in the Sm-rich phase.
The shrinkage of the powder mixtures whose equilibrium phase was the Sm-rich phase was studied, varying sintering time in the range between 1 minute to 240 minutes. This result indicated that sintering occurs by grain boundary diffusion of Co-vacancies.
