Modifying microstructure and magnetic properties of Nd-Fe-B magnet by pressure-assisted sintering

In this paper, microstructure and magnetic properties of Nd-Fe-B magnet were modified by pressure-assisted sintering. The pressure-assisted sintering (PS) and common sintering (CS) were adopted, respectively, and the densifying process and microstructure evolution of magnet with increasing the sintering temperature were clarified. The densified and fine-grained Nd-Fe-B magnet was achieved. The variations of the alignment degree, shrinkage ratio, microstructural characteristics with the magnitude and direction of exerted pressure were revealed. It was demonstrated that the higher density, finer grains and higher alignment degree were achieved in the PS magnet. Especially, the grain boundary microstructure in the PS magnet was significantly improved, in which Nd-rich phases became thin and exhibited net-like distribution, meanwhile, crystal interface became flat and regular. Therefore, high remanence and high coercivity were simultaneously achieved in PS magnet, which were attributed to high density and alignment degree, as well as continuous, flat and straight intergranular phases.