界面调配提高纳米晶复合永磁材料矫顽力的研究

In general, there is a trade-off between magnetization and coercivity in nanocomposite magnets, that is, high magnetization usually accompanied by small coercivity is a major barrier for achieving high-energy products in the magnets . Thus, the simultaneous enhancement of both the magnetization and coercivity is a fundamental challenge in the quest for high performance α-Fe/Nd2Fe14B nanocomposite magnets. The NdCu eutectic alloy or a heavy rare-earth element such as Dy is introduced to the grain boundary in α-Fe/Nd2Fe14B nanocomposite magnets prepared via a hot pressure or hot deformation process compared with thermally annealing. The interfacial structure and composition of the nanocomposite magnets are studied by employing positron lifetime measurements combined with a coincident Doppler broadening (CDB) measurement of the positron-electron annihilation photons. The influence of interfacial structure and composition on the coercivity and energy product is analyzed. The hysteresis loop of the magnets is measured at room temperature using a vibrating sample magnetometer, and their magnetization reversal mechanism was studied by analyzing initial magnetization curves and minor hysteresis loop. In conclusion, the coercivity and energy product of α-Fe/Nd2Fe14B nanocomposite magnets are enhanced by interfical modification such as interfacial structure and composition.

纳米晶复合永磁材料的矫顽力低是制约高性能永磁材料发展的主要原因之一，同步提高磁化强度和矫顽力是进一步提高纳米晶复合永磁材料磁性能的关键。本申请采用热压结合低温退火技术在α-Fe/Nd2Fe14B纳米晶的界面处引入低熔点合金NdCu，利用热变形结合退火技术将重稀土元素Dy扩散至α-Fe/Nd2Fe14B纳米晶的界面处。利用正电子湮灭等研究α-Fe/Nd2Fe14B纳米晶界面结构和成分特征及其控制，研究不同热压/热变形工艺及退火条件下NdFeCoB 合金所制备的α-Fe/Nd2Fe14B纳米晶磁体界面结构和成分的变化规律及其对合金矫顽力和磁能积的影响。测定磁体初始磁化曲线和小磁滞环的矫顽力Hci，根据其磁化强度M和矫顽力Hci随磁化场强度的变化规律来研究纳米晶复合永磁体的矫顽力机制。 本项研究通过α-Fe/Nd2Fe14B纳米晶界面结构和成分的调配来提高纳米晶复合永磁材料矫顽力从而改善其磁能积

本项目瞄准纳米晶复合永磁材料研究中制约这类材料发展的关键问题：软磁相的存在必然导致磁体矫顽力的降低，磁体本身磁化强度和矫顽力间内在的倒置关系开展研究工作。通过对Nd2Fe14B/α-Fe纳米晶磁体矫顽力机制的研究弄清了界面调配提高矫顽力的根本原因。从制备工艺和合金元素等方面进行设计，通过控制熔体快淬过程，采用严重塑性变形结合热退火、热压缩变形等先进技术制备出各向同性和各向异性Nd2Fe14B/-Fe型纳米晶复合永磁材料并进行微结构的控制，即永磁纳米晶的择优取向与软磁纳米晶的良好形态控制及界面结构和化学成分调配。.本项目通过引入低熔点Pr-Cu合金、添加Ti、Nb等合金元素优化磁体的界面结构实现了Nd2Fe14B/α-Fe型纳米复合永磁材料剩磁和矫顽力的同步提高；基于核/壳纳米结构的思想，提出了三维(3D)自组装类核/壳纳米结构的策略，所制备的各向同性纳米晶复合磁体同时具有高的矫顽力和高的剩余磁化强度，最大磁能积(BH)max高达25 MGOe，是目前报道的各向同性Nd2Fe14B/-Fe纳米晶复合磁体的最高值；提出了两步高压热压缩变形技术思想，实现了硬磁相Nd2Fe14B的（00l）织构与高软磁相含量（> 30%）及均匀细小的两相晶粒尺寸和分布的同时控制，制备出最大磁能积为24.3 MGOe的各向异性块体纳米复合磁体，是目前报道的软磁相超过20%的同类型磁体中性能最高的块体纳米复合永磁材料。研究结果对高性能纳米晶复合永磁材料的制备和发展具有重要的意义。