【作者】 王金磊；

【导师】 李福山；

【作者基本信息】 郑州大学 ， 材料加工工程， 2013， 硕士

【摘要】 具有交换耦合作用的NdFeB双相复合永磁材料,以其较高的磁性能引起重视,如何制备低稀土含量且性能优异的NdFeB双相复合永磁材料是目前永磁材料研究方向之一。本文采用熔体快淬法制备出Nd8.5Fe84.5.xNb0.5Zr0.5B6Cux (x=0,0.5,1)三种不同Cu含量的双相复合永磁材料,随后使用DSC、XRD和VSM等方法研究了制备工艺参数和Cu元素的添加对NdFeB双相复合永磁材料显微结构和磁性能的影响。三种的合金快淬速度较大时,快淬条带主要由非晶相组成,晶化过程中形核质点减少,需要克服很大的形核激活能才能形核,致使形核率较低,部分晶粒异常长大,不利于磁性能的提高。当快淬速度较慢时,条带中含有部分先结晶相α-Fe和Fe3B等,在晶化过程中易于长大、粗化,减少软、硬磁相之间的交换比例,影响合金的磁性能。当合金的快淬速度较合适时,合金条带中有适当的结晶相,在晶化退火时可以作为形核的质点,增大形核率同时阻碍晶粒的长大,获得细小均匀的晶粒结构,提高合金的综合磁性能。对于不同Cu含量的合金都有不同的最佳淬速与之对应,Nd8.5Fe84.5Nb0.5Zr0.5B6合金与Nd8.5Fe84Nb0.5Zr0.5B6Cu0.5合金20m／s快淬时磁性能最佳,而Dd8.5Fe83.5Nb0.5Zr0.5B6Cu1合金则25m／s时磁性能较好。本文重点研究了晶化工艺对条带结构和磁性能的影响。晶化温度过高或者晶化时间过长,在晶粒能充分析出但同时也造成晶粒尺寸过大,其比表面积减小,同时易于一些反磁畴的形核,则软、硬磁相之间的交换耦合作用减弱,使合金的磁性能降低。但晶化温度过低或者晶化时间过短,合金非晶相晶化不完全,同时软、硬磁相析出数量较少。非晶相的存在,阻碍软、硬磁相之间的交换耦合作用,影响合金的磁性能的提高。不过对于不同Cu含量的合金,获得最佳磁性能的晶化工艺参数有所不同。Nd8.5Fe84.5Nb0.5Zr0.5B6合金在750℃晶化退火8min后磁性能较佳,其最大磁能积(BH)m=137.21kJ/m3;Nd8.5Fe84Nb0.5B6Cu0.5合金在730℃晶化退火20min磁性能较优,其最大磁能积(BH)m=103.72kJ/m3;而Nd8.5Fe83.5Nb0.5Zr0.5B6Cu1合金在73℃晶化退火15min磁性能较好,其最大磁能积(BH)m=93.71kJ/m3。同时也研究了Cu元素的添加对合金磁性能的影响。通过研究发现,添加cu元素不利于合金综合磁性能的提高。尽管Cu元素的添加,能促发α-Fe相的形核,但在晶化过程中先析出相易于长大、粗大,同时不利于硬磁相的析出,且Cu易于偏聚在软、硬磁相之间,阻碍交换耦合作用,降低合金的磁性能。更多还原

【Abstract】 NdFeB two-phase composite permanent magnetic materials with exchange coupling are brought to the forefront because of their superior magnetic properties. How to prepare NdFeB two-phase composite permanent magnetic materials which have low rare-earth content and excellent properties is one of the research directions of permanent materials. In this study, by using the rapid quenching of melt method, two-phase composite permanent magnetic materials with three different contents of Cu Nd8.5Fe84.5_xNbo.5Zr0.5B6Cux (x=0,0.5,1) are prepared. Then research on the effects of preparation technological parameter and the addition of element Cu on the microstructures and magnetic properties of NdFeB two-phase composite permanent magnetic materials is conducted by DSC、 XRD and VSM.When with a faster quenching speed of the three kinds of alloy, melt-spun ribbons are mainly composed of amorphous phase and the nucleating particles are reduced in the crystallization process, so much nucleation activation energy need to be overcome for nucleation. Then the nucleation rate is very low and some grains grow abnormally, which go against the promotion of magnetic properties. When with a lower quenching speed, some first crystalline phase contended in melt-spun ribbons like a-Fe and Fe3B, etc. is easy to grow and be coarsened in the crystallization process, which reduces the exchange proportion between soft and hard magnetic phase and influence the magnetic properties of the alloy. When with an appropriate quenching speed of the alloy, some proper crystalline phase in the alloy melt-spun ribbons can be seen as nucleating particle in crystallization annealing, increasing the nucleation rate and blocking the grain growth. Then wee and homogeneous grain structure can be obtained, which improves the comprehensive magnetic properties of the alloy. Alloys with different Cu content have different optimum quenching speed. Nd8.5Fe84.5Nb0.5Zr0.5B6and Nd8.5Fe84Nb0.5Zr0.5B6Cu0.5have optimum magnetic properties at the rapid quenching speed of20m/s, while Nd8.5Fe83.5Nb0.5Zr0.5B6Cu1at 25m/s.This study focuses on the research of the effects of crystallization technology on melt-spun ribbons and magnetic properties. When crystallization temperature too high or crystallization time too long, the crystal particles can fully separate out but the crystal particles will be oversized and the specific surface area will be reduced, which benefits the nucleation of some anti-magnetic domain. Then the exchange coupling between soft and hard magnetic phase is weakened and the magnetic properties of the alloy is reduced. While, when crystallization temperature too low or crystallization time too short, amorphous phase crystallization of alloy is incomplete and the soft and hard magnetic phase separate out less. The existence of amorphous phase blocks the exchange coupling between soft and hard magnetic phase, which influences the improvement of alloy magnetic properties. For alloys with different Cu content, the crystallization technology parameters of optimum magnetic properties are different. For Nd8.5Fe84.5Nb0.5Zr0.5B6, the optimum magnetic property is realized8min after crystallization annealing at750℃and the maximum magnetic energy product is (BH)m=137.21kJ/m3. The optimum magnetic property of Nd8.5Fe84Nb0.5Zr0.5B6Cu0.5is realized20min after crystallization annealing at730℃and the maximum magnetic energy product is (BH)m=103.72kJ/m3. The optimum magnetic property of Nd8.5Fe83.5Nb0.5Zr0.5B6Cu1is realized15min after crystallization annealing at730℃and the maximum magnetic energy product is(BH)m=93.71kJ/m3.Besides, this study also discusses the effects of addition of element Cu on alloy magnetic properties. The research result shows that the addition of element Cu goes against the improvement of alloy’s comprehensive magnetic property. The addition of Cu can accelerate the nucleation of a-Fe phase, but the first precipitated phase is easy to grow and be coarsened in the crystallization process, meanwhile, it goes against the precipitation of hard magnetic phase and Cu is easy to gather between the soft and hard magnetic phase, blocking the exchange coupling and reducing alloy’s magnetic properties.更多还原