Bulk Fabrication and Coercivity Enhancement of Ce-Based RE ₂ Fe ₁₄ B Prepared by a Modified Reduction–Diffusion Process

Rare-earth (RE) permanent magnets, particularly Nd₂Fe₁₄B, are essential for various high-performance applications. The supply risks and high price of critical rare-earth elements like Nd, however, have driven the search for alternative RE₂Fe₁₄B (2-14-1) compounds for reducing or replacing the Nd content. In our previous work, we developed a modified reduction-diffusion (R-D) process for synthesizing 2-14-1 phases. Nevertheless, fabricating bulk magnets with enhanced magnetic properties using this method remains challenging due to phase decomposition during sintering. In this study, we directly address this challenge, implementing a dual strategy: particle size refinement and grain boundary engineering. After synthesizing 2-14-1 compounds through the modified R-D process, we applied high-energy ball-milling to refine the particle size, followed by heat-treatment with Ca as a reducing agent to suppress phase decomposition and promote phase recovery. Further improvement of the magnetic properties was achieved through the addition of a low-melting-point Nd₇₀Al₂₀Cu₁₀ alloy, which facilitated the formation of a uniform grain boundary. This modification enhanced magnetic decoupling, resulting in a significant increase in coercivity up to 10 kOe for Ce-based 2-14-1. This comprehensive approach presents a promising pathway for the development of cost-effective and high-performance Ce-based permanent magnets, contributing to the advancement of efficient rare-earth magnets.