电泳沉积晶界扩散钕铁硼磁体磁性及机制研究

发布时间：2018-07-07 10:18

本文选题：烧结Nd-Fe-B磁体 + 电泳沉积　；参考：《武汉大学》2016年博士论文

【摘要】：为满足电动汽车、风力发电机、节能家电等新兴领域对稀土永磁材料的需求、促进稀土资源的高效利用,提高磁体的综合磁性能、减少高矫顽力磁体的重稀土使用量已成为烧结Nd-Fe-B磁体研究领域的重要目标。本文发展了电泳沉积这一新兴的晶界扩散技术,研究了关键工艺过程和稀土含量对磁体性能的影响规律,确定了重稀土化合物DyF3和TbF3的最佳扩散工艺,优化了不同稀土含量磁体的最佳扩散量,阐明了扩散磁体的矫顽力增强机制,研究了扩散磁体的使役性能,制备了低重稀土高矫顽力的烧结Nd-Fe-B磁体,实现了重稀土的高效利用,对电泳沉积晶界扩散磁体的规模化制造和应用具有重要指导意义。主要研究成果如下：1.采用电泳沉积方法,在烧结Nd-Fe-B磁体表面成功制备出均匀、平整、厚度可控的重稀土化合物涂层。确定了电泳沉积晶界扩散DyF3的最佳扩散温度和扩散时间。通过控制温度和时间等扩散工艺参数,磁体的矫顽力从16.1 kOe大幅提高到22.8 kOe。无重稀土磁体中添加少于1.2 wt.% Dy,磁体矫顽力的增加量高于6.5 kOe,重稀土利用效率比常规粉末冶金方法高三倍以上。精确表征了扩散样品中Dy浓度随到磁体表面距离的变化关系,分析表明磁体矫顽力的增加与Dy元素的浓度和分布密切相关。通过微观结构的分析,阐明了矫顽力的增强机制：高温扩散后,Dy元素主要沿晶界扩散进入磁体内部,在主相晶粒外围形成具有高磁晶各向异性场的(Nd, Dy)2Fe14B相,从而显著提高磁体的矫顽力。此外,被Dy替代的Nd元素析出于晶界,晶界相变得更加连续均匀且增厚,使得相邻主相晶粒之间的磁孤立作用增强,进一步提高了磁体的矫顽力。2.利用电泳沉积厚度可控这一优势,系统研究了DyF3涂层厚度和磁体厚度对烧结Nd-Fe-B磁体磁性能和微观结构的影响,初步解决了晶界扩散法仅适用于薄片磁体的局限性。随着涂层厚度的增加,磁体的矫顽力从16.10 kOe逐渐增加到24.04 kOe。通过对涂层厚度的优化,无重稀土磁体中扩散少于1.3wt.%的Dy,磁体矫顽力可显著提高8.0 kOe,与其他方法相比优势明显。由于重稀土元素的扩散深度有限,扩散效果受限于磁体的厚度,研究发现磁体的矫顽力随磁体厚度的增加逐渐降低。当磁体厚度为8.5 mm时,矫顽力增加量仍有3.26 kOe,优于当前见诸报道的最佳结果。从而进一步证实电泳沉积法是一种能够精确控制涂层厚度、经济高效的制备较厚的高矫顽力磁体的方法。3.采用电泳沉积TbF3的方法,系统研究了初始磁体稀土含量对晶界扩散磁体的影响规律,阐明了重稀土元素的扩散机制和扩散磁体的矫顽力增强机制。磁性能结果表明,不同稀土含量磁体的矫顽力都随着涂层厚度的增加先逐渐升高,而后趋于稳定或者降低。稀土量为30wt.%的初始磁体获得的矫顽力增加量最大,添加少于0.81 wt.% Tb时,矫顽力提升10.07 kOe,实现了重稀土的高质化利用。微观结构分析表明稀土量为30wt.%的初始磁体中,稀土量较低,晶界相较少且连续性较弱,扩散后磁体表面形成core-shell结构且深度达500μm,晶界相的连续性显著增强。而稀土量为34wt.%的磁体,扩散后晶界相的改善程度不及稀土量为30wt.%的磁体,因此矫顽力的增加量低于稀土量为30wt.%的磁体,但是晶界扩散少于1.44 wt.% Tb时,磁体的矫顽力高达28.12 kOe,是目前无重稀土晶界扩散磁体矫顽力的最高值。这一工作对优化不同牌号的烧结磁体的最佳扩散效果、制备低重稀土高矫顽力烧结Nd-Fe-B磁体具有重要的指导意义。4.系统研究了晶界扩散对不同稀土含量烧结Nd-Fe-B磁体使役性能的影响规律。高温磁性能测量结果表明扩散后磁体的矫顽力温度系数有明显的降低,温度稳定性得到改善。高温条件下磁体的不可逆磁通损失随稀土含量的增加而降低,晶界扩散样品的不可逆磁通损失显著降低,极大地提高了磁体的使用温度。扩散样品晶界处存在的大量氟化物,提高了磁体的电阻率。
[Abstract]:In order to meet the needs of the rare earth permanent magnets, such as electric vehicles, wind turbines, energy saving appliances and other emerging fields, the efficient utilization of rare earth resources, the improvement of the comprehensive magnetic properties of the magnets and the reduction of the heavy rare-earth use of high coercive magnets have become an important target for the study of the sintered Nd-Fe-B magnets. The influence of the key process and the content of rare earth on the properties of magnets was studied. The best diffusion process of heavy rare earth compounds DyF3 and TbF3 was determined. The best diffusion amount of the magnets with different rare earth content was optimized. The coercive force enhancement mechanism of the diffused magnets was clarified. The performance of the diffusion magnets was studied and the preparation of the diffusion magnets was studied. The sintered Nd-Fe-B magnets with high coercivity of low Re rare-earth and high re coercion have great significance for the large-scale manufacture and application of the electrophoretic deposition of grain boundary diffusion magnets. 1. the main research results are as follows: 1. by electrophoretic deposition, the uniform, smooth and controllable thickness of the sintered Nd-Fe-B magnets was successfully prepared. The best diffusion temperature and diffusion time of DyF3 are determined. By controlling the diffusion process parameters such as temperature and time, the coercive force of the magnet is greatly increased from 16.1 kOe to 22.8 kOe., with less than 1.2 wt.% Dy added to the heavy rare earth magnet, the increase of coercivity of the magnet is higher than 6.5 kOe, and the heavy rare earth is used. The efficiency is more than three times higher than the conventional powder metallurgy. The relationship between the Dy concentration in the diffusion sample and the distance of the magnet surface is precisely characterized. The analysis shows that the increase of the coercivity of the magnets is closely related to the concentration and distribution of the Dy elements. Through the analysis of the microstructure, the strengthening mechanism of the coercive force is clarified: after the high temperature diffusion, the Dy element is the main element. The magnetic field (Nd, Dy) 2Fe14B phase which has high magnetic anisotropy field in the main phase of the main phase is formed along the grain boundary, thus the coercive force of the magnet is greatly improved. In addition, the Nd element replaced by Dy is out of the grain boundary, and the phase transition of the grain boundary is more continuous and thicker, which makes the magnetic isolation between the adjacent main phase grains strengthen and advance. The influence of the thickness of DyF3 coating and the thickness of the magnets on the magnetic properties and microstructure of the sintered Nd-Fe-B magnets is systematically studied by improving the coercive force of the magnet.2.. The effect of the thickness of the coating and the thickness of the magnets on the magnetic properties and microstructure of the sintered Nd-Fe-B magnets is systematically studied. KOe is gradually increased to 24.04 kOe. by optimizing the thickness of the coating. The diffusion of the magnets can be significantly increased by 8 kOe in the non heavy rare earth magnets, and the coercivity of the magnets can be significantly increased by 8 kOe. The diffusion effect of the heavy rare earth elements is limited to the thickness of the magnets. The increase of thickness is gradually reduced. When the thickness of the magnet is 8.5 mm, the increase of coercive force is still 3.26 kOe, which is better than the best results reported at present. Thus, it is further confirmed that electrophoretic deposition is a method to accurately control the thickness of the coating and to prepare the thicker high coercive magnets with economic efficiency,.3. by electrophoretic deposition of TbF3. The effect of the rare earth content on the diffusion magnets at the grain boundary is studied systematically. The diffusion mechanism of heavy rare earth elements and the coercive force enhancement mechanism of the diffused magnets are clarified. The magnetic energy results show that the coercivity of the magnets with different rare earth content increases gradually with the increase of the thickness of the coating, and then tends to stabilize or decrease. The maximum coercivity increased for the initial magnet of 30wt.%, and the coercive force increased by 10.07 kOe when adding less than 0.81 wt.% Tb. The high quality utilization of heavy rare earth was realized. The microstructure analysis showed that the rare earth content was 30wt.%, the rare earth content was lower, the grain boundary phase was less and the continuity was weaker, and the core-shell junction formed after the diffusion of the magnets. With a depth of 500 mu m, the continuity of the grain boundary phase is significantly enhanced. The magnet with a rare earth content of 34wt.% is less than a magnet with a rare earth amount of 30wt.%, so the increase of coercive force is lower than that of a rare earth 30wt.%, but the coercivity of the magnetic field is less than 1.44 wt.% Tb, and the coercive force of the magnet is as high as 28.12 kOe. The highest value of coercive force of non heavy rare earth grain boundary diffusion magnets. This work has important guiding significance to optimize the best diffusion effect of different grades of sintered magnets and prepare Nd-Fe-B magnets with low weight rare earth and high coercive force sintering. The effect of grain boundary diffusion on the performance of Nd-Fe-B magnets with different rare earth content is studied. The measurement results of the temperature and magnetic properties show that the temperature coefficient of the coercive force of the magnets is obviously reduced and the temperature stability is improved. The irreversible flux loss of the magnet decreases with the increase of the rare earth content, and the irreversible flux loss of the grain boundary diffusion sample decreases significantly, which greatly improves the use temperature of the magnets. The presence of a large amount of fluoride at the grain boundary enhances the resistivity of the magnet.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM27

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