Limitations in the grain boundary processing of the recycled HDDR Nd-Fe-B system

Ikram, Awais (author), Awais, Muhammad (author), Sheridan, Richard Stuart (author), Walton, Allan (author), Kobe, Spomenka (author), Pušavec, Franci (author), Žužek Rožman, Kristina (author)

Fully dense spark plasma sintered recycled and fresh HDDR Nd-Fe-B nanocrystalline bulk magnets were processed by surface grain boundary diffusion (GBD) treatment to further augment the coercivity and investigate the underlying diffusion mechanism. The fully dense SPS processed HDDR based magnets were placed in a crucible with varying the eutectic alloys Pr$_{68}$Cu$_{32}$ and Dy$_{70}$Cu$_{30}$ at 2–20 wt. % as direct diffusion source above the ternary transition temperature for GBD processing followed by secondary annealing. The changes in mass gain was analyzed and weighted against the magnetic properties. For the recycled magnet, the coercivity (H$_{Ci}$) values obtained after optimal GBDP yielded ~60% higher than the starting recycled HDDR powder and 17.5% higher than the SPS-ed processed magnets. The fresh MF-15P HDDR Nd-Fe-B based magnets gained 25–36% higher coercivities with Pr-Cu GBDP. The FEG-SEM investigation provided insight on the diffusion depth and EDXS analysis indicated the changes in matrix and intergranular phase composition within the diffusion zone. The mechanism of surface to grain boundary diffusion and the limitations to thorough grain boundary diffusion in the HDDR Nd-Fe-B based bulk magnets were detailed in this study.

• Language: English
• Keywords: rare earth permanent magnets, HDDR Nd$_2$Fe$_{14}$B, recycling, spark plasma sintering, grain boundary diffusion processing (GBDP), high coercivity
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2020
• Number of pages: 17 str.
• Numbering: Vol. 13, iss. 16, art. 3528
• PID: 20.500.12556/RUL-134379
• UDC: 537.6(045)
• ISSN on article: 1996-1944
• DOI: 10.3390/ma13163528
• COBISS.SI-ID: 25316867
• Publication date in RUL: 12.01.2022

Record is a part of a journal

• Title: Materials
• Shortened title: Materials
• Publisher: MDPI
• ISSN: 1996-1944
• COBISS.SI-ID: 33588485

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
• Licensing start date: 10.08.2020

Secondary language

• Language: Slovenian
• Keywords: redki zemeljski trajni magneti, recikliranje, sintranje s plazmo, postopek difuzije meje zrn (GBDP), visoka magnetna koercivnost