Presentation Information
[O2-2]Breaking Performance Limits in Nd-Fe-B Magnets via Extreme Grain Optimization and Grain Boundary Diffusion Synergy
Qingfeng Shan1, *Cong Wang1, Yongjiang Yu1, Bingqiang Shi1, Pengfei Wang1, Yumeng Zhang1, Jianing Wang1, Hang Zhao2 (1. Yantai Zhenghai Magnetic Material Co., Ltd. (China), 2. Institute of Functional Materials, Central Iron & Steel Research Institute (China))
Keywords:
sintered NdFeB,ultra-high comprehensive performance,grain optimization,magnet evaluation
As a key material in modern motor systems, the synergistic regulation of coercivity and heavy rare earth (HRE) content in Nd-Fe-B permanent magnets constitutes a core challenge for industrial applications. This study developed ultra-high-performance magnets through an extreme strategy combining grain optimization and grain boundary phase regulation. A normalized magnet evaluation system (HcJ-RF) was newly established to scientifically assess the intrinsic coercivity of HRE/light rare earth (LRE)-containing Nd-Fe-B diffusion magnets. Experimental results demonstrate that the optimized magnets achieved record-breaking performance: The sum of (BH)max and HcJ exceeded 87, while the normalized coercivity HcJ-RF reached 30 kOe – both representing the highest reported values to date.
Through systematic optimization of processing conditions and alloy composition, the pre-diffusion magnet grain size was refined from 4.82 μm to 2.28 μm with improved size distribution, alongside adjusted ratios of grain boundary phase-forming elements. During Tb diffusion treatment, both optimized and conventional magnets exhibited controlled grain growth, with the optimized version showing superior grain size distribution (σ=1.91 μm). EPMA analysis confirmed continuous Tb-rich grain boundary phases with gradient HRE distribution in optimized magnets. This enabled a BHJ improvement to 87.3 ((BH)max=44.4 MGOe, HcJ=42.9 kOe) without increasing HRE consumption. According to the action law of different rare earth elements on HcJ, the HcJ values under different system conditions in previous work were normalized to the HcJ -RF performance under the condition of the same base material with a heavy rare earth-free formula. The HcJ -RF of the magnets prepared in this work reached 30.3 kOe. Micromagnetic simulations revealed that refined grains and optimized grain boundaries enhance reverse magnetization nucleation fields by reducing demagnetization coupling effects.
This breakthrough highlights the critical role of grain optimization in HRE grain boundary diffusion processes: The decoupled enhancement of remanence and coercivity through extreme grain refinement and boundary phase regulation establishes a new paradigm for cost-effective magnet development. This technology significantly reduces HRE consumption, demonstrating crucial strategic value for balancing rare earth resource utilization.
Through systematic optimization of processing conditions and alloy composition, the pre-diffusion magnet grain size was refined from 4.82 μm to 2.28 μm with improved size distribution, alongside adjusted ratios of grain boundary phase-forming elements. During Tb diffusion treatment, both optimized and conventional magnets exhibited controlled grain growth, with the optimized version showing superior grain size distribution (σ=1.91 μm). EPMA analysis confirmed continuous Tb-rich grain boundary phases with gradient HRE distribution in optimized magnets. This enabled a BHJ improvement to 87.3 ((BH)max=44.4 MGOe, HcJ=42.9 kOe) without increasing HRE consumption. According to the action law of different rare earth elements on HcJ, the HcJ values under different system conditions in previous work were normalized to the HcJ -RF performance under the condition of the same base material with a heavy rare earth-free formula. The HcJ -RF of the magnets prepared in this work reached 30.3 kOe. Micromagnetic simulations revealed that refined grains and optimized grain boundaries enhance reverse magnetization nucleation fields by reducing demagnetization coupling effects.
This breakthrough highlights the critical role of grain optimization in HRE grain boundary diffusion processes: The decoupled enhancement of remanence and coercivity through extreme grain refinement and boundary phase regulation establishes a new paradigm for cost-effective magnet development. This technology significantly reduces HRE consumption, demonstrating crucial strategic value for balancing rare earth resource utilization.
