Tuning the microstructure and magnetic properties of bulk nanocomposite magnets with large strain deformation

In this study, we investigated the effect of strain on the microstructure and magnetic properties of bulk α-Fe/Nd2Fe14B nanocomposite magnets produced by a combination of severe plastic deformation at room temperature and subsequent thermal annealing. Experiment results indicate that severe plastic deformation can induce the formation of α-Fe and Nd2Fe14B nanocrystals in the amorphous matrix and then suppress the formation of metastable intermediate phases during thermal annealing. The volume fraction of α-Fe phase in the magnets increases as the strain increases，and the grain size of α-Fe and Nd2Fe14B phases significantly decreases. As a result, the bulk magnets made at ε=6.2 show enhanced magnetic properties, (BH)max=17.8 MGOe and Hc=7.2 kOe, compared with that of directly annealed partially amorphous (Nd-Pr)-Fe-Co-Nb-B, (BH)max=12.2 MGOe and Hc=6.2 kOe.