The Mechanism of the Effects of Ta Substitution on the NdFeB-based Nanocomposite Alloys

Directly quenched nanocrystalline and partly amorphous ribbons of Nd9Fe86-xB5Tax (x=0,1,2,and 3) alloys were prepared by melt spinning.The effects of Ta substitution on the microstructure and magnetic properties of nanocomposite NdFeB/α-Fe alloy have been investigated.For the directly quenched alloys,1%Ta addition increases the coercivity and maximum energy product,but over 1% Ta substitution decreases the magnetic properties.It was also found that Ta addition did not lead to a decreased mean grain size.To clarify the role of Ta substitution,the crystallization behavior and magnetic properties of partly amorphous alloys were investigated.The results indicated that the addition of Ta increases the crystallization temperature of Nd2Fe14B phase.The deterioration in the magnetic properties for Ta added alloys resulted,at least partly,from the fact that Ta retards the crystallization of hard magnetic phase and leads to over-growth of soft magnetic grains.This is most likely also the reason why the partly amorphous and annealed alloys have much worse properties than those of optimally directly quenched alloys.