基于Nd_(6)Co_(13)Cu晶界重构的高抗蚀性钕铁硼磁体

High Corrosion-resistant NdFeB Permanent Magnet Based on Nd_(6)Co_(13)Cu Grain Boundary Restructuring

抗蚀性差是长期限制多元多相钕铁硼永磁材料应用的关键问题之一。富Nd晶界相电极电位远低于Nd_(2)Fe_(14)B硬磁主相,是导致抗蚀性差的组织结构根源。本文基于晶界重构思路,设计并制备了Nd_(6)Co_(13)Cu(%,原子分数)高电位辅合金和(Pr,Nd)_(28.00)Fe_(bal)B_(1.03)(%,质量分数)低稀土含量的2∶14∶1型主合金,通过双合金方法,制备了不同Nd_(6)Co_(13)Cu添加量的重构磁体,综合磁性能/抗腐蚀性能测试和显微组织结构/成分分析,揭示了重构磁体的性能变化规律和调控机理。结果表明,2%Nd_(6)Co_(13)Cu添加量的重构磁体综合性能优异,总稀土含量仅为28.46%,湿热环境下96 h腐蚀失重仅为0.28 mg/cm^(2),为相同稀土含量未重构磁体的26%,磁性能[B_(r)=14.03 kG,H_(cj)=12.62 kOe,(BH)_(max)=48.55 MGOe]同样优于未重构磁体。在近(Nd,Pr)_(2)Fe_(14)B化学计量比的主合金中加入低熔点Nd_(6)Co_(13)Cu辅合金,可在低总稀土含量的前提下保证磁体的烧结致密度和综合磁性能,大幅降低富Nd相的体积分数,减少腐蚀源,抑制腐蚀沿晶界区域的扩展。此外,高电极电位Nd_(6)Co_(13)Cu添加可增加晶界区域的化学稳定性,降低电化学腐蚀原动力。综上所述,晶界重构方法提供了一种提升钕铁硼磁体抗蚀性的新途径。

Poor corrosion resistance has long been one of the major concerns limiting the wider application of Nd_(2)Fe_(14)B per-manent magnet,which is originated from the multi-phase microstructure as the electrode potential of Nd-rich intergranular phase is much lower than that of Nd,Fex4B matrix phase.In this paper,based on the grain boundary restructuring approach,high-potential Nd_(6)Co_(13)Cu(%,Atom fraction)grain boundary alloy and near-stoichiometric(Pr,Nd)_(28.00)Fe_(bal)B_(1.03)(%,Mass fraction)main alloy with low rare earth content were designed and prepared.By the dual alloy method,restructured magnets with different Nd_(6)Co_(13)Cu additions were prepared.Based on the collected measurements of the magnetic properties and corro-sion resistance,as well as microstructural and compositional analysis,the controlling mechanism of the Nd_(6)Co_(13)Cu restruc-tured magnets was revealed.Results show that the 2%Nd_(6)Co_(13)Cu restructured magnet possesses excellent comprehensive per-formance with the total rare earth content(TREC)of merely 28.46%,low mass loss in 96 h test in hot and humid corrosive environment(0.28 mg/cm^(2),26%of the value for the un-restructured magnet with the same TREC),and superior magnetic properties(B_(r)=14.03 kG,H_(cj)=12.62 kOe,(BH)_(max)=48.55 MCOe)compared to the un-restructured magnet.The addition of low-melting-point Nd_(6)Co_(13)Cu alloy to the near-stoichiometric 2:14:1-type main alloy guarantees the high density and comprehensive magnetic properties at low TREC,which significantly reduces the volume fraction of vulnerable Nd-rich phase,lowers the corrosion source,and suppresses the corrosion propagation along the grain boundary region.Besides,the addition of high-electrode-potential Nd_(6)Co_(13)Cu also increases the chemical stability of grain boundary region and reduces the electrochemi-cal corrosion activity.In summary,the proposed grain boundary restructuring approach provides a feasible way towards high corrosion-resistant NdFeB magnets.