Presentation Information
[P1-25]Synthesis of Fine (Nd,Ce)2Fe14B Powders via the Reduction-Diffusion Process For Fabricating Ce-substituted Nd-Fe-B Sintered Magnets
*Jeong Hyun Kim1, Kyung-Shik Yoon1, Hyeon Seong Kim1, Hee Yeon Jeon1, Tae-Hoon Kim2, Young-In Lee1 (1. Seoul National University of Science and Technology (Korea), 2. Korea Institute of Materials Science (Korea))
Keywords:
Nd,Ce-Fe-B sintered magnets,Reduction-Diffusion process,Grain refinement
Nd-Fe-B sintered magnets have been widely used in advanced technologies, such as electric vehicles and renewable energy systems, due to their excellent magnetic properties. The increasing demand for permanent magnets, combined with the growing instability in Nd supply, has driven the exploration for alternative rare-earth elements. Ce- or La-substitution for Nd in Nd-Fe-B magnets has become a promising solution to resource supply issues, as these elements are naturally more abundant. However, Ce2Fe14B exhibits inferior intrinsic magnetic properties compared to Nd2Fe14B, leading to reductions in remanence and coercivity in Ce-substituted magnets. To improve the cost performance of Ce-substituted magnets, microstructural control is essential. In particular, grain refinement plays a critical role in enhancing coercivity, as the coercivity mechanism in Nd-Fe-B magnets transits to coherent rotation when grains approach the single-domain size.
Research on the grain-refined Ce-substituted magnets has focused on the hot-deformation process using rapidly solidified ribbons. Optimized Ce substitution and microstructure in hot-deformed magnets with a grain size of about 200 nm have shown a high magnetic property comparable to N42M-grade. However, the hot-deformation process faces limitations in scalability and cost, making the development of the sintering process essential for the industrial production of Ce-substituted magnets. Reducing the grain size of Ce-substituted sintered magnets is limited by the 3-5 μm of NdCe-Fe-B particle size produced through jet milling. Therefore, synthesizing (Nd,Ce)2Fe14B powder with a particle size below 1 μm via the reduction-diffusion (R-D) process is necessary to achieve grain refinement. A few studies have demonstrated the feasibility of synthesizing Ce-substituted powders via the R-D process; however, research on producing (Nd,Ce)2Fe14B single-phase powders with appropriate particle sizes is still limited, and no studies have been reported on the fabrication of Ce-substituted sintered magnets from R-D powders.
In this study, (Nd,Ce)2Fe14B powders were synthesized by optimizing the R-D process using Nd-Ce oxides, enabling the fabrication of Ce-substituted sintered magnets with a single main phase (SMP) structure with homogeneously distributed Nd and Ce atoms within the grains. Compared to the R-D process using elemental precursors, the use of Nd-Ce oxides increased the Ce substitution ratio to 27% while maintaining the 2-14-1 phase. Also, the synthesized (Nd0.73Ce0.27)2Fe14B powder had an average particle size of 1.2 μm. Furthermore, a press-less sintering (PLP) process was applied to the (Nd0.73Ce0.27)2Fe14B powders, and the sintering behavior of the Ce-substituted magnets was systematically analyzed. The results demonstrate that fabricating PLP sintered magnets using Ce-substituted 2-14-1 powders synthesized by the R-D process provides insights into the development of grain refinement techniques for Nd-reduced magnets.
Research on the grain-refined Ce-substituted magnets has focused on the hot-deformation process using rapidly solidified ribbons. Optimized Ce substitution and microstructure in hot-deformed magnets with a grain size of about 200 nm have shown a high magnetic property comparable to N42M-grade. However, the hot-deformation process faces limitations in scalability and cost, making the development of the sintering process essential for the industrial production of Ce-substituted magnets. Reducing the grain size of Ce-substituted sintered magnets is limited by the 3-5 μm of NdCe-Fe-B particle size produced through jet milling. Therefore, synthesizing (Nd,Ce)2Fe14B powder with a particle size below 1 μm via the reduction-diffusion (R-D) process is necessary to achieve grain refinement. A few studies have demonstrated the feasibility of synthesizing Ce-substituted powders via the R-D process; however, research on producing (Nd,Ce)2Fe14B single-phase powders with appropriate particle sizes is still limited, and no studies have been reported on the fabrication of Ce-substituted sintered magnets from R-D powders.
In this study, (Nd,Ce)2Fe14B powders were synthesized by optimizing the R-D process using Nd-Ce oxides, enabling the fabrication of Ce-substituted sintered magnets with a single main phase (SMP) structure with homogeneously distributed Nd and Ce atoms within the grains. Compared to the R-D process using elemental precursors, the use of Nd-Ce oxides increased the Ce substitution ratio to 27% while maintaining the 2-14-1 phase. Also, the synthesized (Nd0.73Ce0.27)2Fe14B powder had an average particle size of 1.2 μm. Furthermore, a press-less sintering (PLP) process was applied to the (Nd0.73Ce0.27)2Fe14B powders, and the sintering behavior of the Ce-substituted magnets was systematically analyzed. The results demonstrate that fabricating PLP sintered magnets using Ce-substituted 2-14-1 powders synthesized by the R-D process provides insights into the development of grain refinement techniques for Nd-reduced magnets.