2002 Volume 43 Issue 3 Pages 589-592
The microstructure and magnetic properties of nanocrystalline Fe42.5Co42.5Nb7B8 alloy were investigated. The bcc nanocrystalline alloy obtained by annealing the amorphous precursor at 873 K for 3.6 ks exhibits a high saturation magnetization (Is) of 1.90 T and a lower coercivity (Hc) of 60 A/m. It also exhibits a very high Curie temperature (Tc) more than 1173 K. The structure of the nanocrystalline alloy was found by high-resolution transmission electron microscopy (HRTEM) to consist of a mixture of nearly spherical bcc grains with sizes of 5 to 10 nm. HRTEM combined with EDS and nano-beam electron diffraction with a diameter of 2 nm revealed that the amount of Nb in the intergranular amorphous phase was larger than that in the bcc grain. The segregation of Nb element in the intergranular amorphous phase increases the thermal stability of the amorphous phase and suppresses the grain growth of the bcc phase. The high thermal stability of the structure and the high Curie temperature are promising for soft magnetic material for high temperature application.