热流变钕铁硼块状磁体及辐向磁环的研究

发布时间：2018-05-28 07:59

本文选题：Nd-Fe-B + 热压/热流变　；参考：《钢铁研究总院》2017年硕士论文

【摘要】：热压/热流变工艺是制备全密度和纳米晶各向异性钕铁硼永磁材料的有效方法。并且利用热流变钕铁硼磁体沿着压力方向取向的特点,可以制备辐向永磁环。但是纳米晶磁体的矫顽力并不高,未能达到理论的预期值,若要更进一步扩大热流变钕铁硼永磁体的应用范围,需要对热流变磁体的矫顽力机理及增强矫顽力的方法进行研究与探索。本文通过调整热流变过程的流变温度、流变速率等工艺参数,并将Nd-Fe-B与Pr-Cu混合粉末进行热压/热流变处理,以对磁体的制备工艺及矫顽力的机制进行研究。同时,通过改善反向挤压工艺,最终制备了无裂纹的各向异性钕铁硼辐向永磁环。全文主要结论如下:(1)热流变块状磁体的磁性能随着流变速率的增加呈现先增加后减小的趋势,并在流变速率为0.0050s-1时达到最优性能。SEM观察表明,晶粒在流变速率为0.0050s-1时排布最为规整。XRD图谱及沿不同方向的磁化曲线都表明块状磁体在流变速率为0.0050s-1时取向度最好。(2)少量添加Pr-Cu后,磁体的矫顽力提升效果明显。通过对微观结构TEM的观察,发现添加Pr-Cu后,主相片状晶粒间的富稀土层变厚,晶粒尺寸变小,并有Pr-Cu富集现象。通过测量外加磁场与磁体的c轴呈不同夹角时的磁滞回线,发现热流变钕铁硼磁体的矫顽力机制由形核机制及钉扎机制共同作用,并且在添加Pr-Cu后,形核机制增强,钉扎机制减弱。(3)通过调整反向挤压工艺,最终制备了厚壁且无裂纹的辐向磁环。分析了辐向磁环的不均匀性的原因,认为辐向磁环的不均匀性可通过模具设计等一系列方法来加以改进。从磁环的顶部(上端)到底部(下端)位置,磁性能先增加后减小,并在距离磁环顶部为总高度3/4的位置,磁性能达到最高。挤压速率从1.33mm/s变化至1.03mm/s的过程,在磁环的相同位置,磁性能都增大。挤压速率为1.03mm/s时,在距离磁环顶部为总高度3/4的位置时,磁性能为Br=12.83 kGs,Hcj=16.39kOe,(BH)max=36.09MGOe。SEM 显示,挤压速率高时,磁体晶粒排布混乱,不规则;挤压速率低时,晶粒排布更为规则。(4)磁环沿着直径(磁环外表面至内表面)方向,越靠近内表面,矫顽力越低,剩磁越高,SEM显示,在贴近内表面位置,磁体晶粒排布更为规则,在贴近外表面,晶粒排布较为混乱。
[Abstract]:Hot pressing / thermal rheological process is an effective method for preparing NdFeB magnets with full density and nanocrystalline anisotropy. The radial permanent magnetic rings can be prepared by using the heat flux NdFeB magnets along the direction of pressure orientation. However, the coercivity of nanocrystalline magnets is not high and fails to reach the expected theoretical value. If we want to further expand the application scope of Nd-Fe-B permanent magnets with heat flux, The coercivity mechanism and the methods to enhance the coercivity of heat flux magnets need to be studied and explored. In this paper, the preparation process and coercivity mechanism of magnets were studied by adjusting the rheological temperature and rheological rate of the heat rheological process, and the mixture of Nd-Fe-B and Pr-Cu powder was treated by hot pressing / hot rheological treatment. At the same time, the crack free anisotropic NdFeB radial permanent magnetic ring was prepared by improving the reverse extrusion process. The main conclusions of this paper are as follows: (1) the magnetic properties of the heat flux bulk magnets increase first and then decrease with the increase of rheological rate, and the optimum properties are obtained when the rheological rate is 0.0050s-1. When the grain flow rate is 0.0050s-1, the most regular .XRD pattern and the magnetization curves along different directions show that the coercivity enhancement effect of bulk magnets is obvious after adding a small amount of Pr-Cu to the bulk magnets with the best orientation when the rheological rate is 0.0050s-1. By observing the microstructure of TEM, it is found that after the addition of Pr-Cu, the rare-earth rich layer between the main photo grains becomes thicker, the grain size becomes smaller and the Pr-Cu is enriched. By measuring the hysteresis loop of the magnetic field at different angles to the c axis of the magnet, it is found that the coercivity mechanism of the heat flux NdFeB magnets is combined with nucleation mechanism and pinning mechanism, and the nucleation mechanism is enhanced after the addition of Pr-Cu. By adjusting the reverse extrusion process, the radial magnetic ring with thick wall and no crack was finally prepared by adjusting the pinning mechanism. The reasons for the inhomogeneity of the radial magnetic ring are analyzed. It is considered that the inhomogeneity of the radial magnetic ring can be improved by a series of methods such as die design and so on. From the top (top end) to the bottom (bottom end) position of the magnetic ring, the magnetic performance first increases and then decreases, and the magnetic performance reaches the highest when the total height is 3 / 4 from the top of the ring. When the extrusion rate changes from 1.33mm/s to 1.03mm/s, the magnetic properties increase at the same position of the magnetic ring. When the extrusion rate is 1.03mm/s, when the total height is 3 / 4 from the top of the magnetic ring, the magnetic property is Br=12.83 kGsSU Hcjn 16.39kOeOEN (Br=12.83) 36.09MGOe.SEM shows that, when the extrusion rate is high, the distribution of the magnets is chaotic and irregular, and when the extrusion rate is low, the magnetic properties of the magnets are irregular, and the results show that when the extrusion rate is high, the magnetic properties of the magnets are irregular. The closer the inner surface, the lower the coercivity, and the higher the remanence, the more regular the distribution of the magnets is, and the closer the outer surface, the more regular the distribution of the magnets is, and the more regular the magnetic grains are, the more regular the magnetic grains are in the direction of the diameter (outer surface to the inner surface) of the magnetic ring, and the lower the coercive force is, the higher the remanence is, The grain distribution is more chaotic.
【学位授予单位】：钢铁研究总院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM273

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