Effect of additives on thermal stability of Nd-Fe-B bonded magnets (abstract)

Abstract

Effects of Zr and Nb on magnetic properties and thermal stability were studied for Nd-Fe-B bonded magnets. Bonded magnets with a composition of Ndx(Fe94-x-y)B6Ty, where T=Zr and Nb; x=11.0, 11.5, and 12.0; y=0, 0.5, 1.0, 1.5, and 2.0; were prepared by using melt spun ribbons. The addition of Zr up to 0.5 at .% increased the (BH)max of the bonded magnets, and further addition of Zr decreased the (BH)max at each Nd content level. Hci increased monotonously with an increase in Zr. (BH)max and Hci of the Nb containing bonded magnets also showed similar behavior. Irreversible flux loss after exposure at 180 °C for 1000 h significantly reduced with an increase in the Zr content at each Nd content level. Both the structural flux loss and the thermal fluctuation flux loss were reduced with an increase in the Zr content. An irreversible flux loss of about 5% was obtained when the Nd and Zr content were 11.5 at .% and 2.0 at. %, respectively. A similar value of irreversible flux loss was also obtained in Nb containing bonded magnets with the same composition. It was found that the oxygen pickup by the bonded magnets during the heat resistant test was well correlated to the structural loss of the bonded magnets. A structural flux loss of less than 3% was obtained when the oxygen pickup was less than 0.4 wt. % for both additives. SEM studies revealed that the grain size of the 2-14-1 phase observed in the additive-containing specimens was finer than that of the base alloy.