Misorientations across boundary planes in a sintered NdFeB permanent magnet

Abstract

From the perspective of crystallography, there exist crystals as well as boundary planes in NdFeB permanent magnets and accordingly, there should exist orientation textures of Nd₂Fe₁₄B crystals and orientation texture of boundary planes. This work therefore aims to study the misorientations across boundary planes in a sintered NdFeB permanent magnet. As an interdisciplinary study, serial stereological methods are developed to extract more structural information from the material and as the result, spreading wetting and penetration of Nd-Rich phases to the Nd₂Fe₁₄B phase are quantificationally characterized. The entire boundaries are sorted into Nd₂Fe₁₄B/Nd₂Fe₁₄B grain boundaries (N/N boundaries) and Nd₂Fe₁₄B/(thin-layer-like)Nd-Rich phase boundaries (N/R boundaries). 31°/[0 0 1] and 60°/[0 0 1] twist boundaries are preferred among N/N boundaries, while 31°/[0 0 1] and 72°/[0 0 1] misorientations are preferred among N/R boundaries. The structural features of these misorientations are elaborated via the Five Parameter Analysis (FPA) method. The potential correlations between the grain boundary plane distributions (GBPDs) and magnetic properties are then discussed regarding how the anisotropic features at boundary locations impact coercivity, domain and remanence.