资源节约型稀土永磁材料的高性能化研究

发布时间：2018-01-06 15:39

本文关键词：资源节约型稀土永磁材料的高性能化研究　出处：《浙江大学》2017年博士论文　论文类型：学位论文

【摘要】：钕铁硼是目前磁性最强、应用最广、消耗稀土最多的永磁材料。钕铁硼的多年快速增长,导致我国稀土资源利用极不平衡,其高度依赖的Nd、Pr、Dy、Tb等昂贵稀土资源日益紧缺,而Ce、La等廉价的高丰度稀土则大量积压。减少昂贵的重稀土 Tb、Dy和扩大高丰度的Ce、La在钕铁硼中的应用,发展低成本高性能磁体,已成为稀土永磁材料基础研究的重要方向。钕铁硼的强磁性源于2:14:1四方相的内禀硬磁性。为满足高温应用,通常在Nd-Fe-B中添加大量的重稀土 Tb/Dy提高2:14:1相的各向异性场以提高矫顽力,但它导致磁能积降低,且显著增加成本;另一方面,Ce/La_2Fe_(14)B相的内禀磁性远弱于Nd/Pr2Fe14B,过去在钕铁硼中极少使用。因此,如何在不用或者尽可能少用Dy/Tb的情况下获得高矫顽力和抑制添加Ce/La导致的磁稀释效应是研制低成本高性能磁体的重要挑战。针对上述问题,本文从“减法”和“加法”两方面着手,开展了资源节约型稀土永磁材料的高性能化研究:一是通过设计含Dy的新晶界相,实现Dy在液相烧结过程中向主相晶粒边界层扩散,增强局域各向异性,极大降低了高矫顽力磁体中重稀土用量;二是构筑多主相结构,即Ce在2:14:1相中非均匀取代Nd,利用不同内禀磁性主相间的磁耦合作用增强磁性能,成功研制出高Ce取代量的高性能磁体。主要创新点如下:设计了(Pr,Dy,Cu)-H_x氢化物,重构Nd-Fe-B磁体晶界相,基于脱氢后元素的商活性实现Dy向主相边界层的商效扩散,增强局域磁晶各向异性,显著提商了重稀土在高矫顽力磁体中的利用效率。传统的直接重稀土合金化方法制备高矫顽力磁体(～20 kOe),需要添加2.0 at.%左右的Dy。晶界添加纯金属元素Dy或者含Dy合金粉末,在烧结和热处理过程中,Dy除了部分的向2:14:1主相晶粒扩散,依旧有大量的Dy元素在晶界上富集,导致了重稀土元素的利用效率低。本文设计了 Dy浓度较低的晶界相氢化物(Pr,Dy,Cu)-H_x,在高温烧结和热处理扩散过程中,利用氢化物脱氢后的高活性,使重稀土元素Dy向主相边界层高效扩散,并降低Dy元素在晶界相中的浓度,在仅添加0.32 at.%的Dy时,矫顽力力从15.0 kOe提升到18.2 kOe,提升幅度为21.3%,单位原子百分比的Dy对矫顽力的贡献高达10.9 kOe,有效提高了重稀土元素Dy的利用效率。在掌握多主相Nd-Ce-Fe-B磁体的磁性能变化规律的基础上,成功制备出高Ce取代量的商性能烧结磁体。采用双主相工艺,Ce和Nd在主相中高度非均匀分布,主相间的长程磁相互作用使磁体磁性能尤其是矫顽力远高于相同平均成分、Ce在主相中均匀分布的单主相磁体。发现少量的Ce取代,多主相磁体退磁曲线的方形度Kk/Hcj下降较多。随Ce取代量提高,磁体在反磁化过程中表现出类似“单相”的行为,方形度得以回复到94%以上。此外,多主相磁体的热处理工艺对磁性能的影响更为复杂:一方面,热处理改善晶界相分布状态,有利于抑制主相晶粒间的短程磁相互作用(提高矫顽力);另一方面,热处理进一步促进稀土元素在主相晶粒间的互扩散,趋向形成与单主相磁体类似的Ce均分分布,弱化主相间的长程磁相互作用(降低矫顽力)。基于两种作用的竞争关系,通过改善和优化烧结和热处理工艺,在保持Ce非均匀分布的多主相结构的同时形成连续均匀分布的晶界相,成功制备出高Ce取代量、高性能的RE-Fe-B多主相烧结磁体,当45wt.%Ce取代Nd时,磁体的综合磁性能依旧保持在Hcj=9.0kOe,Br=12.4kG,(BH)max=36.7MGOe。掌握了高Ce取代量RE-Fe-B磁体的晶界相组织演变规律,并揭示了其对磁性能作用机理。除了多主相磁体中晶粒间的长程磁相互作用外,晶界相显微组织对磁性能尤其是矫顽力也有重要影响。本文发现在高Ce取代量的Nd-Ce-Fe-B磁粉中出现少量的REFe_2相,遗传到最后的多主相磁体中,以连续的晶界相组织分布在2:14:1相晶粒间,对磁体的矫顽力起正面作用。由于REFe_2相熔点(978℃)低于2:14:1相,在高温(1030℃)烧结过程中熔化,增加了液相体积分数,改善了晶界相与主相之间的润湿性,形成了连续分布晶界相,弱化主相晶粒之间的短程磁相互作用。洛伦兹透射电镜(L-TEM)证明了晶界组织的优化可以有效抑制晶粒之间短程交换作用;不同主相晶粒之间长程的静磁相互作用依旧存在,从而在反磁化过程中,有效各向异性强的主相晶粒抑制各向异性弱的晶粒磁化翻转。上述两个因素对保持多主相烧结磁体的矫顽力都具有重要作用。
[Abstract]:NdFeB magnetic current is the strongest, the most widely used, the consumption of rare-earth permanent magnet material. Most of the years of NdFeB rapid growth, resulting in rare earth resource utilization in China is extremely uneven, which is highly dependent on the Nd, Pr, Dy, Tb and other expensive rare earth resources become increasingly scarce, while Ce, La and other cheap high the abundance of rare earth overstock. Less expensive heavy rare earth Tb, Dy and the expansion of high abundance of Ce, the application of La in the development of NdFeB magnets, high performance and low cost, has become an important direction of rare earth permanent magnet materials research. The ferromagnetic source of NdFeB in tetragonal 2:14:1 intrinsic hard magnetic. To meet the high temperature application, usually with heavy rare earth Tb/Dy in a lot of Nd-Fe-B to improve the anisotropy field of 2:14:1 phase to improve the coercivity, but it leads to lower energy product, and significantly increase the cost; on the other hand, Ce/La_2Fe_ (14) B is the intrinsic magnetic properties is much weaker than in the past Nd/Pr2Fe14B, nd iron Boron rarely used. Therefore, how to use or as little as possible with Dy/Tb under the condition of high coercive force and magnetic inhibition caused by Ce/La dilution effect is an important challenge for development of low cost high performance magnets. Aiming at the above problems, this article from the "subtraction" and "addition" two aspects to carry out. Study on high performance resource conservation of rare earth permanent magnet materials: one is through the new grain boundary design phase containing Dy, Dy in the liquid phase sintering process to the main phase grain boundary layer diffusion, enhanced local anisotropy, which greatly reduces the amount of heavy rare earth magnets with high coercivity; two is to build a multi main phase the structure of Ce in 2:14:1 phase, non uniform to replace Nd, using magnetic coupling different intrinsic magnetic properties and magnetic properties of main reinforced, successfully developed a high amount of Ce to replace the high performance magnets. The main innovations are as follows: Design (Pr, Dy, Cu) -H_x hydride, Nd- reconstruction Fe-B grain boundary phase, the dehydrogenation of elements taking the activities of Dy to the main phase boundary layer diffusion based on business efficiency, enhance the local magnetic anisotropy, improve business efficiency in high coercivity magnets. The heavy rare earth direct heavy rare earth alloying the traditional method of preparing high coercivity magnets (20 ~ kOe), need to add the Dy. grain boundaries around 2 at.% with pure metal Dy or Dy containing alloy powder during sintering and heat treatment process, in addition to the part of the Dy diffusion to the 2:14:1 main phase grain, there is still a large number of Dy elements enriched in grain boundaries, resulting in a heavy rare earth element utilization efficiency is low grain boundary. This paper designed the lower concentration of Dy phase (Pr, Dy, Cu by -H_x), in high temperature sintering and thermal diffusion process, high activity after using hydride dehydrogenation, the heavy rare earth element Dy to the main phase boundary layer, diffusion, and reduce the Dy element in the grain boundary phase concentration Only in degree, adding 0.32 at.% of Dy, the coercivity force increased from 15 kOe to 18.2 kOe, to enhance the rate of 21.3% units, atomic percentage of Dy contribution to the coercive force of up to 10.9 kOe, effectively improve the utilization efficiency of heavy rare earth elements Dy. Based the variation in magnetic multi master master Nd-Ce-Fe-B magnet on the successful preparation of high performance sintered magnets Ce to replace the taking amount. By double main phase process, Ce and Nd in the primary phase of highly inhomogeneous distribution, long-range magnetic interaction and main magnetic properties especially the coercivity is much higher than that of the same average composition, in uniform distribution of Ce the main phase of the single phase magnet. Found a small amount of Ce substitution, multiple main magnets of the demagnetization curve rectangularity of Kk/Hcj decreased more. With the Ce content increased, the magnet in the reversal process showed a similar "phase" behavior, to return to more than 94% square degrees. In addition, many Effect of heat treatment on the magnetic properties of the magnet main phase is more complex: on the one hand, the heat treatment improved the grain boundary phase distribution, is conducive to inhibit the interaction between the main phase grain short-range (magnetic coercivity improving); on the other hand, to further promote the heat treatment of rare earth elements in the main phase grain diffusion, tend to form with the single main magnets of Ce were similar distribution, interaction and weak main Cheng Ci (lower coercivity). Competition between the two effects on, by improving and optimizing the sintering and heat treatment process, while maintaining the Ce non uniformly distributed multi main phase structure at the same time the formation of grain boundary continuous uniform distribution the phase was successfully prepared by high Ce content, high performance RE-Fe-B main phase sintered magnets, when 45wt.%Ce replaced Nd, integrated magnets can remain in the Hcj=9.0kOe, Br=12.4kG, max=36.7MGOe. (BH) have high Ce content RE-Fe-B magnet The grain boundary phase microstructure evolution, and reveal the mechanism of magnetic properties. In addition to the main phase in the magnet long-range magnetic interaction between grain and grain boundary phase microstructure on magnetic properties especially the coercivity have an important influence. The paper found that instead of a small amount of REFe_2 phase Nd-Ce-Fe-B magnetic powder in Ce, to the end of the main phase of genetic multi magnet, with continuous grain boundary phase tissue distribution in 2:14:1 grains, the coercive force plays a positive role. Due to the REFe_2 phase (978 DEG C) below the melting point of 2:14:1 phase at high temperature (1030 DEG C) melting and sintering process, adding liquid volume fraction, grain boundary phase and improve the wettability between the main phase, forming a continuous distribution of grain boundary phase, weakening the interaction between the main phase grains. Lorenz short-range magnetic transmission electron microscopy (L-TEM) proved that the optimal organization can restrain the grain boundary between the short-range exchange Effect; magnetostatic interaction still exists in long range between different main phase grain, resulting in the magnetization reversal process, effective strong anisotropy of main phase grain inhibiting grain magnetization reversal. Weak anisotropy plays an important role in the above two factors to keep the main phase of sintered magnet coercivity.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM273

【参考文献】