MAGNETIC-PROPERTIES AND MICROSTRUCTURES OF SPRAYED SMCO5 MAGNETS EXPOSED TO INTERMEDIATE TEMPERATURES

The hysteresis observed in Hci from cycling SmCo5 magnets at temperatures of 650-800 °C has been shown to result from an inability to completely redissolve the precipitated phase (Sm2Co 17) at the higher temperature in the short time that has been allowed. It has, therefore, been concluded that the rate of Sm 2Co17 precipitation is higher than that of dissolution at these temperatures. Metallographic observations made on plasma-sprayed SmCo 5 magnets (after exposing them for time periods of a few hours to several weeks at these temperatures) show that the precipitated phase exists as discrete second-phase particles in the material unlike in sintered magnets where extensive Sm2Co17 precipitation is observed at grain boundaries. It is suggested that the striations observed in micrographs of SmCo5 magnets (after exposure to these temperatures) are the result of strain processes related to thermal-expansion mismatch of neighboring grains.