CORROSION OF NDFEB PERMANENT-MAGNETS IN HUMID ENVIRONMENTS AT TEMPERATURES UP TO 150-DEGREES-C

The corrosion of NdFeB permanent magnets has been investigated in oxidizing environments containing controlled additions of water vapor in the temperature range 79-155 degrees C under conditions where no condensation of electrolyte occurs. The corrosion occurs by intergranular attack leading to formation of pits. No significant corrosion was observed in dry environments at temperatures up to 155 degrees C, indicating that H2O vapor is necessary to produce corrosion. Much higher corrosion rates were measured in Ar-20% O-2-water vapor gas mixtures at 145 degrees C than in air-water vapor mixtures at the same temperature, indicating that nitrogen inhibits the attack. The rate of attack in the Ar-20% O-2-water vapor environment increased with time of exposure.