Magnetic properties evolution with grain boundary phase transformation and their growth in Nd-Fe-Cu-Ga-B sintered magnet during post-sinter annealing process. (October 2021)

• Record Type: Journal Article
• Authors: Fu, Song; Liu, Xiaolian; Jin, Jiaying; Zhang, Zhiheng; Liu, Yongsheng; Yan, Mi
• Is Part Of: Intermetallics. Volume 137(2021)
• Publication Date: 2021-10
• Subjects: A. Functional alloys -- B. Annealing -- Magnetic properties -- C. Powder metallurgy -- D. grain boundary -- Segregation; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2021.107303
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: The formation of Nd6 Fe13 Ga phase promoted the continuity and non-ferromagnetism of grain boundary (GB) phases of Nd-Fe-Cu-Ga-B magnets during proper post-sintering annealing process. The coercivity increased dramatically with a decrease of remanence. After further annealing at the sintering temperature, the remanence recovered with a drop of coercivity. It indicated that Nd2 Fe14 B phase decomposed with the formation of Nd6 Fe13 Ga phase. Overextending the annealing time led to the gradual decrease of coercivity as the growth of Nd6 Fe13 Ga phase weakened the continuity of GB phases. Increasing the annealing temperature to the optimum temperature for Nd6 Fe13 Ga phase can aggravate the decrease of coercivity and remanence. Owing to the intensifying segregation of Ga and Fe in GB phases with the formation of Nd6 Fe13 Ga phase by dehydrogenation (HD) at 560 °C, high coercivity can be obtained by annealing at a lower temperature or for shorter time compared with HD at 480 °C. The enrichment of Cu in Nd-rich phase ensured its wettability and non-ferromagnetism when the diffusion of Fe and Ga became more local with the formation of Nd6 Fe13 Ga phase. Therefore, the combined effect of Cu doping and reasonable high temperature HD was conducive to obtain high coercivity in a larger range of annealing time and temperature for Nd-Fe-Ga-B magnet, which was a potential method for its mass production. Highlights: Cu segregated with Ga and Fe during the formation of Nd6 Fe13 Ga phase. Nd6 Fe13 Ga grew with extending annealing time and decreased the coercivity. Dehydrogenation at 560 °C accelerated phase transition and coercivity increase. Cu enrichment in Nd-rich phase enhanced its wettability and non-ferromagnetism. Cu doping and high temperature HD expanded the proper annealing conditions.