Texture development and grain boundary phase formation in Ce- and Ce-La-substituted Nd-Fe-B magnets during hot-deformation process. (1st November 2022)

• Record Type: Journal Article
• Authors: Kim, Ga-Yeong; Kim, Tae-Hoon; Cha, Hee-Ryoung; Lee, Sang-hyub; Kim, Dong-Hwan; Kim, Yang-Do; Lee, Jung-Goo
• Is Part Of: Journal of materials science & technology. Volume 126(2022)
• Page Start: 71
• Page End: 79
• Publication Date: 2022-11-01
• Subjects: Nd-Fe-B magnets -- Hot-deformation -- Nd-saving -- Ce-substitution -- La-substitution -- Infiltration; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2022.04.006
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: The Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets hinder the texture development and grain boundary phase formation during the hot-deformation process. The decrease in volume fraction of RE-rich liquid in the grain boundaries by Ce- and Ce-La substitution is a critical reason for the deterioration of magnetic and microstructural properties of Ce- and Ce-La-substituted Nd-Fe-B hot-deformed magnets. Based on the results, a method to increase both the coercivity and remanence of the Ce- and Ce-La-substituted Nd-saving hot-deformed magnets was developed: intermediate infiltration (I-infiltration). Abstract: In this study, the influence of Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets on their magnetic and microstructural changes in the course of the hot-deformation process was investigated to gain insight into further reducing the Nd content in fine-grained Nd-Fe-B hot-deformed magnets. We found that the [001] texture and microstructure of the RE-rich grain boundary phases, which are the factors that determine the remanence and coercivity of hot-deformed magnets, were deteriorated by the Ce- and Ce-La-substitution. This is because the volume fraction of the RE-rich liquid formed in the grain boundaries during the hot-press and hot-deformation decreased due to the Ce- and Ce-La-substitution, thereby increasing the friction between the 2:14:1 grains while the c -axes of grains were aligned by grain rotation and decreasing the RE concentration of grain boundary phases. In particular, the Ce-La-co-substitution further prevented the liquid formation within the grain boundaries of the magnets during hot-press and hot-deformation because the wettability of the RE-rich liquid on the 2:14:1 grains became poor when La was substituted for Nd in the 2:14:1 grains. These results indicate that there is room for further improvement in both the remanence and coercivity of the Ce- and Ce-La-substituted magnets by introducing additional liquid into the grain boundaries prior to hot-press and hot-deformation. By applying the Nd-Cu infiltration process to the melt-spun ribbons (intermediate infiltration, I-infiltration), both the remanence and coercivity of the Nd-saving (Nd0.7 Ce0.3 )-Fe-B and (Nd0.7 Ce0.225 La0.075 )-Fe-B hot-deformed magnets were successfully improved.