硼含量对镓掺杂烧结钕铁硼微观结构及磁性能的影响

Effect of boron content on the microstructure and magnetic properties of Ga-doped sintered Nd-Fe-B magnets

采用粉末冶金工艺制备了不同硼含量(质量分数)的高镓掺杂无重稀土烧结钕铁硼磁体,研究了硼的成分变化对物相构成、磁体微观结构及磁性能的影响。结果表明,在硼的质量分数从0.90%逐渐增加到1.00%过程中,磁体的矫顽力呈明显下降趋势,且在硼质量分数超过0.94%后,磁体性能发生急剧恶化;微观结构分析显示,当硼质量分数较低时,材料中有大量Nd6Fe13Ga相形成,晶界相宽度较宽且其分布连续性明显优于高硼含量磁体,硼质量分数的增加明显抑制了Nd_(6)Fe_(13)Ga相的形成,材料中晶界相体积分数降低,晶界物相由非铁磁相向铁磁相转变;进一步结合微磁学模拟证实,构建非铁磁性晶界相和较宽的晶界相宽度以降低Nd_(2)Fe_(14)B主相晶粒间的交换耦合作用是保障磁体具备高矫顽力的关键所在。

High Ga-doped heavy rare earth free sintered Nd-Fe-B magnets with the different boron contents(mass fraction)were prepared by powder metallurgy method in this work.The effect of boron content on phase formation,microstructure,and magnetic properties of the magnets was investigated.Results show that the coercivity of the Ga-doped sintered Nd-Fe-B magnets decreases as the boron content increases from 0.90%to 1.00%.The magnetic properties deteriorate drastically when the boron content exceeds0.94%.Microstructure studies show that the significant amount of Nd_(6)Fe_(13)Ga phases are present and the grain boundary broadens when the boron content is low.The increase of boron content inhibits the formation of Nd_(6)Fe_(13)Ga phase,which leads to the transformation of grain boundary from non-ferromagnetic to ferromagnetic and the volume fraction decrease of the grain boundary phase.Further micromagnetics simulation confirms that the construction of the non-ferromagnetic grain boundary phase and the wider grain boundary phase can reduce the exchange-coupling interaction between the Nd_(2)Fe_(14)B main phase grains,which is critical to ensure the high coercivity of the magnets.