热变形钕铁硼永磁材料的纳米晶结构与矫顽力的关联性研究

The scarcity of the natural resource of heavy rare earth restricts the high temperature applications of Nd-Fe-B magnets. Therefore, enhancing the coercivity of heavy-rare-earth-free or heavy-rare-earth-lean Nd-Fe-B permanent magnets and improving the temperature coefficient of coercivity become research hotspots recently. The Nd-Fe-B magnets prepared by hot pressing and hot deformation process have nano scale lamellar grains, so it has the potential to prepare the high coercivity magnets without the addition of heavy rare earth elements. But the coercivity of the hot deformed Nd-Fe-B magnets without the heavy rare earth is relatively low at present, generally only 10kOe to 15kOe. Low melting point alloy grain boundary diffusion technology can improve the coercivity, but it is generally at the cost of the remanence. The project will prepare heavy-rare-earth-free hot deformation Nd-Fe-B magnets with both high remanence and high coercivity, based on the previous research of the composition, microstructure, and magnetic properties. Firstly, we will study the magnetization reversal behavior of the hot deformation Nd-Fe-B magnet through the micromagnetism finite element simulation, and it will be clarified the relationship between the intrinsic coercivity and the microstructure, such as grain size, grain shape, texture and grain boundary. By adding elements and accuracy control of hot deformation process, the microstructure of hot deformation nanocrystalline Nd-Fe-B magnets will be regulated effectively. The purpose of this project is to explore an effective way to prepare high coercivity Nd-Fe-B magnets without the addition of heavy rare earth elements.

重稀土是制约钕铁硼高温应用的瓶颈，不用或少用重稀土元素制备高使用温度的钕铁硼磁体是当前的研究热点。热压/热变形工艺制备的钕铁硼磁体具有纳米量级的片状晶粒，在不添加重稀土元素的前提下，具备制备高矫顽力磁体的潜力。目前不含重稀土的热变形钕铁硼磁体的矫顽力较低，一般只有10kOe到15kOe。本项目通过热变形钕铁硼磁体的反磁化行为的微磁学模拟，弄清热变形钕铁硼磁体的晶粒大小与形状、取向织构、晶界等与内禀矫顽力的内在关系；然后通过元素添加、热变形工艺的精确控制，实现热变形纳米晶钕铁硼磁体微观组织结构的有效调控从而获得高矫顽力的钕铁硼磁体。最终我们拟探索无重稀土高矫顽力钕铁硼永磁材料的制备新途径，制备出具有高矫顽力的无重稀土纳米晶钕铁硼磁体。

热压/热变形稀土永磁材料是我国稀土永磁材料方面的短板，目前还未实现工业化生产。热压/热变形是制备各向异性稀土永磁材料的一种重要工艺方法，具有与烧结磁体磁性能相当，低成本，短流程近终成型，耐腐蚀性好等优势，极适用于EPS电机、伺服电机及新能源汽车驱动电机等新兴应用领域。与烧结稀土永磁工艺不同，热压/热变形方法无需外界磁场取向即可获得各向异性磁体，织构的形成伴随着晶粒长大同步进行，这种类似于轧制而又兼具致密化的特点恰恰是热变形工艺所特有的，也与Nd-Fe-B自身的特性有关。快淬-热压-热变形是热压各向异性磁体的关键工艺步骤，在这三个工艺过程中材料的微观结构发生巨大的变化，最终磁体的磁性能，特别是内禀矫顽力与微观结构密切相关。. 本项目通过对热压/热变形钕铁硼永磁材料的微观结构及其反磁化行为的深入研究，初步阐明了热压/热变形磁体的晶粒大小与形状、取向织构、晶界等微观结构参数与内禀矫顽力的关联，并初步研究了磁体制备过程中的微观结构演变规律，并通过元素的添加、热变形工艺的精确控制实现了高性能、高矫顽力热变形磁体的可控制备，并尝试了应用热压/热变形工艺制备无重稀土高矫顽力钕铁硼永磁材料。本项目取得了一些较重要的成果：（a）研究了热压/热变形钕铁硼磁体的变形机理，通过实验证实了晶粒旋转和取向长大模型。（b）对Nd-Fe-B热变形磁体取向晶粒的形成过程进行了研究，主要着眼于热变形磁体中异常晶粒的形成及其在变形过程中的变化，异常晶粒的存在也同样影响着磁体各向异性的形成。（c）初步阐明了快淬-热压-热变形过程中，微观结构的演变规律。（d）、获得了高性能的热压/热变形磁体，最优的磁性能达到了Br=14.94 kGs, Hcj=7.80 kOe, (BH)max=54.16 MGOe，为国内最高水平。. 本项目的研究成果对我国热压/热变形钕铁硼磁体的产业化具有一定的指导意义，热压/热变形磁体有望在高功率密度伺服电机、新能源驱动电机、惯性导航、高性能电磁阀门等民用及军用领域得到广泛应用。