THE TERNARY-SYSTEM SM-CO-ZR ISOPLETHIC SECTION AT CO=89AT.PERCENT

A knowledge of solid-liquid equilibria is necessary to optimise sinter ing temperature in industrial Sm2Co17-type magnets. A single-phase sta te is reported as precursor of the cellular microstructure of the Sm2C o17 permanent magnets. The formation of this phase at high temperature seems for a large part to be governed by Zr addition. In order to und erstand the behaviour of 2:17-type magnets, phase relationships have b een investigated in the Co-rich field of the Sm-Co-Zr system. The 1150 degrees C isothermal section has been reinvestigated. A two-phase reg ion was observed involving hexagonal and rhombohedral Sm2Co17. An isop lethic section has been drawn for temperatures between 1150 degrees C and the melting points of the alloy with Co=89 at.%, (Sm + Zr) = 11 at .%. Two four-phase equilibria have been observed. A tentative polyther mal representation of the Sm-Co-Zr system in the Co-rich field has bee n drawn.