THE INFLUENCE OF ZRO2 ADDITION ON PHASE-COMPOSITION IN THE ND-DY-FE-BSYSTEM AND IMPROVED CORROSION-RESISTANCE OF THE MAGNETS

The positive influence of ZrO2 addition on the magnetic properties, te mperature coefficients and corrosion resistance of Nd-Dy-Fe-B magnets were established. The improvements in these parameters were attributed to microstructural changes. The phase composition was analyzed using HREM, and besides the known phases an additional Zr boride phase was f ound, which was identified using crystal structure analysis as a ZrB2 plate -like phase. Due to the formation of the new phase and oxidation of Nd from the Nd -rich grain boundary phase, the sensitivity of the grain boundaries is diminished to a great extent, and as a consequence the corrosion process does not proceed in the sample. It remains limi ted to the exposed surface, which is a worthwhile contribution to the improvement of the resistance against corrosive conditions.