Coercivity enhancement by low oxygen content graphene addition in hot-deformed Nd-Fe-B magnets

• Published in: Journal of magnetism and magnetic materials Vol. 511; p. 166940
• Main Authors: Yang, Qiaosen, Wang, Renquan, Liu, Ying, Li, Jun, Chen, Hongxing, Yang, Xiaojiao
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2020; Elsevier BV
• Subjects: Coercivity; Deformation effects; Ferrous alloys; Grain boundaries; Grain growth; Graphene; Heat treatment; Hot-deformation; Low oxygen content graphene nanoplatelets; Magnetic materials; Magnetic properties; Magnets; Microstructure; Nd-Fe-B; Neodymium; Oxidation; Oxygen; Oxygen content; Remanence; Thermal conductivity; Low oxygen content graphene nanoplatelets; Hot-deformation; Microstructure; Nd-Fe-B; Coercivity
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2020.166940

•By doping 0.2 wt% graphene nanoplates (GNPs) with heat treatment, the magnets exhibited a significant enhancement of coercivity from 12.24 to 16.62 kOe, yet remanence remained almost unchanged.•The thermal conductivity of samples was remarkably improved after doping GNPs.•The grain size significantly reduced after doping GNPs. The amount of free oxygen carried by the GNPs would affect the size and orientation of the interface grains. The effects of oxygen content in graphene nanoplatelets (GNPs) on the microstructure and magnetic properties of hot-deformed (HDed) Nd-Fe-B magnets were investigated in this work. The GNPs were heat treated at 500 °C to effectively reduce the oxygen content from 27000 ppm (GNP-R) to 7768 ppm (GNP-H). Compared with adding the same amount of GNP-R, the GNP-H doped magnet possessed finer and better texture grains at the contact interface of original powders. The coercivity of GNP-H doped magnet was enhanced from 14.16 kOe to 16.62 kOe, and the remanence increased from 13.18 kGs to 13.61 kGs. Owing to the high thermal conductivity of GNP-H doped magnet, the heat transferred between the grains more quickly and thus restraining the grain growth. Therefore, the GNP-H doped magnet got a higher coercivity. The observation of microstructure revealed that the adsorbed oxygen on the surface of GNP-R reacted with Nd-rich phase. It would result in the oxidation of Nd-rich phase and the decreasing of Nd-rich phase at the grain boundaries. Because of inadequate liquid Nd-rich phase, the Nd2Fe14B grains were difficult to complete the dissolution-reprecipitation. Consequently, a high oxygen environment would deteriorate the orientation of grains.