Phase evolution, microstructure and magnetic properties of bulk α-Fe/Nd2Fe14B nanocomposite magnets prepared by severe plastic deformation and thermal annealing.

In this study, the phase evolution, microstructure and magnetic properties of bulk α-Fe/Nd 2 Fe 14 B nanocomposite magnets prepared by a combination of severe plastic deformation (SPD) and thermal annealing have been investigated. Experimental results demonstrate that SPD affects the phase evolution of (Nd,Pr)-Fe-Co-Nb-B alloy upon annealing significantly. The formation of metastable intermediate phases, such as Nd 2 Fe 23 B 3 and Fe 3 B, in the alloy has been effectively inhibited as the strain ε is increased to ε = 6.1, yielding a high volume fraction of α-Fe phase ( V c ∼ 37%) in the bulk α-Fe/Nd 2 Fe 14 B magnets. The grain size of α-Fe and Nd 2 Fe 14 B phases in the magnets decreases with increasing strain. A smaller grain size d = 13.3 nm for α-Fe and 26.5 nm for Nd 2 Fe 14 B is achieved at ε = 6.1, and the magnets show the magnetic properties, ( BH ) max = 14.9 MGOe and H c = 6.4 kOe, larger than those in the α-Fe/Nd 2 Fe 14 B magnets made by directly annealing amorphous ribbons, ( BH ) max = 10.3 MGOe and H c = 4.6 kOe. The enhanced coercivity in the SPD magnets results from an increase in domain-wall-pinning strength. [ABSTRACT FROM AUTHOR]