Effects of strain ratio and stain rate on microstructure and magnetic properties of Nd-Fe-B nanocrystalline magnets during hot-deformation process

This study investigates the effects of strain ratio and strain rate on microstructure and magnetic properties of Nd-Fe-B nanocrystalline magnets during hot-deformation process. The consolidated Nd-Fe-Ga-Co-B isotropic magnet is prepared by hot-pressing under 100 MPa in a vacuum. Field emission scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometry are used for characterization. Observations show that the remanence and coercivity tended to increase and decrease with increasing strain ratio, respectively. Moreover, remanence increases while coercivity decreases as strain rate decreases. These results indicate that slow strain rate is favorable for improvement of remanence with well-aligned grains. However, a change in grain boundary phase as thinned Nd-rich phase is a major drawback, caused by increasing strain ratio including extended deformation time in slow strain-rate hot-deformation process.