Correlation between microstructural heterogeneity and energy product in hot deformed Nd-Fe-B magnets

Abstract

We systematically investigated the local crystallographic texture, magnetic domain structure, and the associated magnetic reversal process of different regions, namely fine-grain (FG), coarse-grain (CG), and large-grain (LG) regions in hot-deformed Nd-Fe-B magnets. The FG region possesses the strongest (00 l) texture and plays a dominant role on the magnetic properties. In contrast, the CG region with partially aligned sub-micron grains and the LG region with randomly aligned micro-sized grains exhibit much weaker (00 l) texture, where the reversal magnetic domains primarily nucleate, deteriorating the remanence and the squareness of the demagnetization curve seriously. This finding highlights a new strategy to achieve high energy density in hot-deformed Nd-Fe-B magnets, i.e. maximizing the volume fraction of highly (00 l) textured FG regions and reducing the undesirable CG and LG regions. Our further experiment enhancing the maximum energy product of the magnet from 42.6 to 51.1 MGOe through optimizing the microstructure homogeneity unambiguously demonstrates the general applicability of the strategy.