Jiaying Jin, Mengfan Bu, Zhiheng Zhang, Hansheng Chen, Simon P. Ringer, Liang Zhou, Wang Chen, Mi Yan
{"title":"Intergranular phase transformation in post-sinter annealed Nd–Dy–Fe–Cu–Ga–B magnet: from Ia3¯-cubic to I4/mcm-tetragonal structure","authors":"Jiaying Jin, Mengfan Bu, Zhiheng Zhang, Hansheng Chen, Simon P. Ringer, Liang Zhou, Wang Chen, Mi Yan","doi":"10.1016/j.actamat.2024.120493","DOIUrl":null,"url":null,"abstract":"High-coercivity Nd–Fe–B permanent magnets crucially depend on the deliberate modulation of intergranular phases, an important embodiment being <em>I</em>4/<em>mcm</em>-tetragonal Nd<sub>6</sub>Fe<sub>13</sub>Ga intergranular phase in the Nd–Fe–Ga–B magnet. Particularly, for the Nd–Dy–Fe–Cu–Ga–B magnet containing multiple rare earths (RE) and alloying metals (M), understanding the evolution of RE<sub>6</sub>(Fe,M)<sub>14</sub> intergranular phase becomes more critical in the quest for higher coercivity. Here we design the (Nd,Pr)<sub>29.0</sub>Dy<sub>3.0</sub>Fe<sub>bal</sub>Cu<sub>0.5</sub>Ga<sub>0.5</sub>B<sub>0.9</sub>N<sub>1.15</sub> (N=Co, Al, Zr, wt.%) as-sintered magnets, where the major RE/Cu/Ga-rich <em>I</em>a<span><math><mover accent=\"true\" is=\"true\"><mn is=\"true\">3</mn><mo is=\"true\">¯</mo></mover></math></span>-cubic intergranular phase is agglomerated in triple junctions. These pristine as-sintered magnets are subjected to annealing over a wide temperature range (390∼900 °C for 3 h) and quenching over a wide time range (0.5∼12 h at 460 °C). Through systematic microstructural characterization and first-principle calculation, the intergranular phase transformation from RE/Cu/Ga-rich <em>I</em>a<span><math><mover accent=\"true\" is=\"true\"><mn is=\"true\">3</mn><mo is=\"true\">¯</mo></mover></math></span>-cubic to Fe/Ga-rich <em>I</em>4/<em>mcm</em>-tetragonal structure, and accompanying elemental segregation is unveiled. During post-sinter annealing, metastable state I firstly occurs, consisting of nanostructured RE/Cu-rich <em>I</em>a<span><math><mover accent=\"true\" is=\"true\"><mn is=\"true\">3</mn><mo is=\"true\">¯</mo></mover></math></span>-cubic and <em>I</em>4/<em>mcm</em>-tetragonal lamellas, with the emergence of multi-twins and coherent interface. Then it evolves into metastable state II, consisting of lath-shaped Fe/Cu/Ga-rich <em>I</em>4/<em>mcm</em>-tetragonal structure with fluctuating Fe/Cu concentrations. Simultaneously, metastable state III occurs, exhibiting <em>P</em>4-tetragonal platelets with lower Cu content and reduced crystallographic symmetry. Finally, heightened Fe/Ga diffusion into the lattice of tetragonal phase with synchronous Cu discharge generates the thermodynamically more stable Fe/Ga-rich RE<sub>6</sub>Fe<sub>13</sub>Ga phase. The implication of phase transformation pathways on the coercivity is discussed, offering valuable insights into the optimization of RE<sub>6</sub>(Fe,M)<sub>14</sub> intergranular phase and allowing more space for enhanced coercivity.","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":null,"pages":null},"PeriodicalIF":8.3000,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Acta Materialia","FirstCategoryId":"88","ListUrlMain":"https://doi.org/10.1016/j.actamat.2024.120493","RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
High-coercivity Nd–Fe–B permanent magnets crucially depend on the deliberate modulation of intergranular phases, an important embodiment being I4/mcm-tetragonal Nd6Fe13Ga intergranular phase in the Nd–Fe–Ga–B magnet. Particularly, for the Nd–Dy–Fe–Cu–Ga–B magnet containing multiple rare earths (RE) and alloying metals (M), understanding the evolution of RE6(Fe,M)14 intergranular phase becomes more critical in the quest for higher coercivity. Here we design the (Nd,Pr)29.0Dy3.0FebalCu0.5Ga0.5B0.9N1.15 (N=Co, Al, Zr, wt.%) as-sintered magnets, where the major RE/Cu/Ga-rich Ia-cubic intergranular phase is agglomerated in triple junctions. These pristine as-sintered magnets are subjected to annealing over a wide temperature range (390∼900 °C for 3 h) and quenching over a wide time range (0.5∼12 h at 460 °C). Through systematic microstructural characterization and first-principle calculation, the intergranular phase transformation from RE/Cu/Ga-rich Ia-cubic to Fe/Ga-rich I4/mcm-tetragonal structure, and accompanying elemental segregation is unveiled. During post-sinter annealing, metastable state I firstly occurs, consisting of nanostructured RE/Cu-rich Ia-cubic and I4/mcm-tetragonal lamellas, with the emergence of multi-twins and coherent interface. Then it evolves into metastable state II, consisting of lath-shaped Fe/Cu/Ga-rich I4/mcm-tetragonal structure with fluctuating Fe/Cu concentrations. Simultaneously, metastable state III occurs, exhibiting P4-tetragonal platelets with lower Cu content and reduced crystallographic symmetry. Finally, heightened Fe/Ga diffusion into the lattice of tetragonal phase with synchronous Cu discharge generates the thermodynamically more stable Fe/Ga-rich RE6Fe13Ga phase. The implication of phase transformation pathways on the coercivity is discussed, offering valuable insights into the optimization of RE6(Fe,M)14 intergranular phase and allowing more space for enhanced coercivity.
期刊介绍:
Acta Materialia serves as a platform for publishing full-length, original papers and commissioned overviews that contribute to a profound understanding of the correlation between the processing, structure, and properties of inorganic materials. The journal seeks papers with high impact potential or those that significantly propel the field forward. The scope includes the atomic and molecular arrangements, chemical and electronic structures, and microstructure of materials, focusing on their mechanical or functional behavior across all length scales, including nanostructures.