Improvement of size and magnetic properties of Nd_(9.5)Fe_(72.5)Ti_3B_(15) bulk magnets by Zr or Nb substitution for Ti

摘要

Magnetic properties and microstructure of directly quenched Nd_(9.5)Fe_(72.5)Ti_(3_x)M)xB_(15) (M=Nb and Zr; x=0-3) bulk magnets in rod form with a diameter of 0.9 mm have been studied. Proper Nb or Zr substitution for Ti has been found to well modify phase constitution and to refine the grain size from 200 to 50-100 nm effectively. Accordingly, the magnetic properties of the rods are enhanced remarkably from _iH_c = 6.2 kOe and (BH)_(max)=5.6 MGOe for Nd_(9.5)Fe_(72.5)Ti_3B_(15) to i_H_c =6.7-15.4 kOe and (BH)_(max)=6.0-8.2 MG Oe for Nd_(9.5)Fe_(72.5)Ti_(3-x)M_xB_(15). The optimum magnetic properties of B_r = 6.6 kG, _iH_c=9.6 kOe, and (BH)_(max)=8.2 MG Oe can be achieved for Nd_(9.5)Fe_(72.5)Ti_(2.5)Zr_(0.5)B_(15) alloy, while the highest coercivity of i_H_c=15.4 kOe [B_r=5.9 kG and (BH)_(max)=7.0 MG Oe] is obtained for Nd_(9.5)Fe_(72.5)Nb_3B_(15). Their high permanent magnetic property arises mainly from the existence of a large volume fraction of 2:14:1 phase, finer grain size, and the existence of grain boundary phase.