Study on Ce₂Fe₁₄B-based sintered magnets with Ce/RE> 80.

Area of Science:

• Materials Science
• Metallurgy
• Permanent Magnets

Background:

• Development of Ce/RE > 80% sintered permanent magnets faces challenges due to deteriorated microstructures.
• The presence of a tetragonal B-rich phase (fct-RE₅Fe₁₈B₁₈) in grain boundaries disrupts RE-rich phase continuity.
• This phase likely forms via a peritectic reaction at 797 °C, negatively impacting magnet performance.

Purpose of the Study:

• To investigate the role of minor neodymium (Nd) substitution in Ce-rich sintered magnets (Ce/RE > 80%).
• To explore methods for improving the microstructure and magnetic properties of these magnets.
• To assess the feasibility of large-scale utilization of cerium (Ce) in permanent magnets.

Main Methods:

• Investigated Ce_25.5∼31.5Nd_0∼5Fe_bal.B_1.25M_1.15 (wt.%) sintered magnets with high Ce content (Ce/RE > 80%).
• Analyzed the effect of direct Nd addition versus blending NdH_x powders during jet milling (JM).
• Characterized microstructural evolution and magnetic properties (coercivity, remanence, maximum energy product).

Main Results:

• Direct Nd addition (3-5%) did not significantly improve microstructure or coercivity in high Ce magnets.
• Blending 2% NdH_x powders into Ce_27.5Nd₃Fe_bal.B_1.25M_1.15 resulted in uniform grain boundaries and Nd-rich shells.
• Achieved excellent magnetic properties: H_cj = 1.714 kOe, B_r = 9.395 kG, (BH)_max = 11.16 MGOe for Ce_27.5Nd₃+2% NdH_x magnet (Ce = 84.5 wt% of RE).

Conclusions:

• NdH_x powder blending is an effective strategy to enhance microstructure and magnetic properties in high Ce sintered magnets.
• This method promotes uniform grain boundary phase distribution and Nd enrichment, overcoming limitations of direct Nd addition.
• The findings support the large-scale application of Ce in permanent magnets by improving process/microstructure design.