压力诱导液相扩散调控热变形钕铁硼晶界相及其对矫顽力机制的影响

The coercivity of hot deformed magnets can be remarkably enhanced by infiltrating liquid phase along grain boundaries. It suggests an effective technology to develop the low cost heavy RE-free Nd-Fe-B magnets with high stability which meets the requirements in energy conservation and emissions reduction and new energy fields. However, the uncontrolled diffusion process resulted from the random diffusion of liquid phase in hot deformed magnets will lead to a high proportion of grain boundary and then an obvious reduction of remanence. In this project, considering the regular shape of plate-like grains in hot deformed Nd-Fe-B magnets, the pressure induced infiltration of low eutectic alloys will be introduced to regulate the spatial distribution and chemical composition of the intergranular phase. At the pressure induced diffusion process, the liquid phase will be enforced to assemble in grain boundaries parallel to C-axis and reduce the existence between flat surfaces of platelets. Meanwhile, the microstructure, micro-magnetic structures and magnetic behaviors will be synthetically analyzed to make clear the relationship between the nucleation and propagation of reversed magnetic domains and magnetic properties and microstructures of magnets. Furthermore, the analysis will reveal the effect of distribution, composition and magnetism of grain boundary phase on intergranular coupling interaction and coercivity mechanism. This project will provide theoretical guidance and experiment experience for microstructure and coericivity modification and it is helpful to obtain a high coercivity without reduction of remanence in hot deformed Nd-Fe-B magnets.

晶界液相扩散可以显著提升热变形钕铁硼永磁体矫顽力，为满足节能减排和新能源领域应用需求、发展低成本的无重稀土高稳定性钕铁硼永磁材料提供了技术途径，但自由扩散无法控制扩散量与晶界相的空间分布，导致晶界相比例过高，剩磁下降显著。本项目利用热变形磁体相对规则的片状晶结构，采用压力诱导低共晶点液相合金沿晶界扩散，探索调控晶界相的空间分布与化学组分的关键技术，在扩散过程中强制将液相引入片状晶短轴侧面，增强畴壁钉扎效果，同时压缩片状晶基面的晶界相含量并强化片状晶有序堆垛，保持高剩磁。通过综合研究显微结构、微磁结构，以及宏观磁化行为，将反磁化畴的形成与拓展与材料的磁性能和显微组织关联起来，揭示热变形磁体晶界相分布、成分与磁性对晶粒间磁耦合的影响规律，研究矫顽力及其调控机制，为调控微结构和矫顽力提供理论指导和实验经验，实现晶界相的高效利用，达到提高矫顽力且保持高剩磁的目的。

钕铁硼永磁体矫顽力与材料的晶粒尺寸、晶界结构有着密切的关系。为了获得较高的矫顽力，通常采用重稀土晶界扩散技术或低共晶点合金晶界扩散技术。在热变形磁体中，无约束晶界扩散无法控制扩散量与晶界相的空间分布，导致晶界相比例过高，剩磁下降显著，发展晶界相在热变形磁体中择优分布工艺是研究热变形磁体矫顽力机制的关键。. 因此为了开展热变形磁体矫顽力提升的同时不显著降低磁体的剩磁的研究，本项目利用热变形磁体相对规则的片状晶结构，采用压力诱导低共晶点液相合金沿晶界扩散，在扩散过程中强制将液相引入片状晶短轴侧面，增强畴壁钉扎效果，同时压缩片状晶基面的晶界相含量并强化片状晶有序堆垛，从而保持高剩磁。为了进一步研究压力辅助作用下晶界相的择优分布，采用快淬粉晶界扩散预处理技术，压力诱导复合结构磁体制备技术，压力诱导重稀土晶界扩散技术，揭示热变形磁体晶界相化学组分、空间分布与磁性等对主相晶粒间磁耦合的影响规律，阐明热变形磁体矫顽力机制。为了提高磁体的剩磁，进行了热变形磁体微观结构优化研究，通过抑制粗晶区，优化磁体的织构取向度。在此基础上，高剩磁的无重稀土热变形钕铁硼磁体。