Journal article
Microstructure of shell and grain boundary phase in Nd-Fe-B sintered magnets grain boundary diffusion processed with low-melting LRE-Al-Cu (LRE = La and Pr) alloys
Materials characterization, Vol.216, p.114249
10/2024
DOI: 10.1016/j.matchar.2024.114249
Abstract
We report magnetic and microstructural changes in Nd-Fe-B sintered magnets after the grain boundary diffusion process (GBDP) of low-melting LRE-Al-Cu alloys [LRE (Light Rare-earth) = La and Pr]. A distinctive microstructural feature of the magnets GBD treated with La-Al-Cu (LAC) and Pr-Al-Cu (PAC) were characterized via the electron probe microanalysis and high-angle annular dark-field scanning transmission electron microscopy analysis at a depth of 50 μm from the magnet surface. The formation of a thick high-anisotropy Pr-Al-rich shell was clearly observed in the PAC-GBDP magnets, whereas there was no distinct shell formation in the LAC-GBDP magnets. La, Al, and Cu were dissolved in the Nd-rich grain boundary phase (GBP) rather than in the main phase, thereby thickening the GBP. This resulted in a difference in the coercivity gain between PAC-GBDP (+6.4 kOe) and LAC-GBDP (+3.3 kOe). The point to note here is that the remanence reduction induced by LAC-GBDP (−0.2 kG) is much smaller than that induced by PAC-GBDP (−1.2 kG) because the grain boundary diffused La-Al-Cu, which can dilute the saturation magnetization of the Nd2Fe14B (2–14-1) crystal, does not dissolve into 2–14-1. Furthermore, the squareness of demagnetization curves of the LAC-GBDP magnets (98%) was much improved than that of the PAC-GBDP magnets (86%). This is because chemically induced liquid film migration (CILFM), an undesirable grain growth phenomenon induced by shell formation, does not occur in LAC-GBDP magnets. In conclusion, the deterioration in remanence and squareness, which are serious problems in the LRE-GBDP, can be minimized by the LAC-GBDP; thus, the utilization of La in the GBDP is a promising method for obtaining a high maximum energy product of the magnets. Based on the results of this analytical work, we propose a guide for developing a cost-effective novel GBDP source that can prevent grain growth by CILFM and increase the magnetocrystalline anisotropy of the shell.
•The distinct microstructure of the grain boundary diffused (GBD) magnets with La-Al-Cu and Pr-Al-Cu were characterized.•Pr-Al-Cu causes undesirable grain growth from Pr-Al-rich shell formation by Chemically induced liquid film migration (CILFM).•La-Al-Cu prevents CILFM and concentrated at the grain boundary, thereby maintaining high remanence and squareness.•Novel cost-effective La-based GBD source was proposed for enhanced magnetic performance.
Details
- Title: Subtitle
- Microstructure of shell and grain boundary phase in Nd-Fe-B sintered magnets grain boundary diffusion processed with low-melting LRE-Al-Cu (LRE = La and Pr) alloys
- Creators
- Ye Ryeong Jang - Yonsei UniversityTae-Hoon Kim - Korea Institute of Materials ScienceJeongmin Kim - Daegu Gyeongbuk Institute of Science and TechnologyHyun-sook Lee - Yonsei UniversityKyungmi Lee - Yonsei UniversityJong Wook Roh - Kyungpook National UniversityTae-Suk Jang - Sun Moon UniversityWooyoung Lee - Yonsei University
- Resource Type
- Journal article
- Publication Details
- Materials characterization, Vol.216, p.114249
- DOI
- 10.1016/j.matchar.2024.114249
- ISSN
- 1044-5803
- eISSN
- 1873-4189
- Publisher
- Elsevier Inc
- Language
- English
- Date published
- 10/2024
- Academic Unit
- Nursing
- Record Identifier
- 9985219295302771
Metrics
1 Record Views