Post-sintering heat treatment effect on the coercivity of sintered (Nd,Dy)(15)(Fe,Co,Mo,Al)(77)B-8 permanent magnets

The effect of heat treatment on the intrinsic coercivity. H-i(c) and micros tructure were investigated for sintered (Nd,Dy)(15)(Fe,Co,Mo,AI)(77) Bg per manent magnet. The microstructure has been investigated by scanning electro n microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray spectrosc opy and Mossbauer spectroscopy. The observed behaviour of H-i(c) may be cau sed by a superposition of the following effects: (i) the distribution of th e nonmagnetic phases and the ratio of the amount of hard magnetic Nd2Fe14B- phase to the amount of the residual phases; (ii) homogeneous distribution o f elements in the main phases; (iii) removing the stresses in the phases; a nd (iv) diffusion of AI, Mo and Co into the hard magnetic Nd2Fe14B-phases. (C) 2000 Elsevier Science S.A. AII rights reserved.