永磁材料晶界改性与磁性能、耐腐蚀性能研究

发布时间：2018-04-06 07:14

本文选题：晶界添加MgO　切入点：优化晶界显微组织　出处：《太原科技大学》2014年硕士论文

【摘要】：钕铁硼永磁材料应用于我国的各个领域，大到我国的航天工程，小到人们的日常生活，随着更多基于钕铁硼功能器件的开发，将会有更多的商品出现在我们周围。我国稀土资源储备丰富，钕铁硼产业有很好的基础，发展前途光明。但是目前我国钕铁硼产业的自主知识产权还比较少，高端产品落于美国和日本，加大对它的研究势在必行。本文制备的磁体在真空烧结炉内烧结而成，与双合金法相似，基体的成分为：(PrNd)30Gd3Al0.8B1.03Fe余。在真空手套箱里将MgO按不同比例与制备的基体磁粉混合，并用球磨机球磨，然后将混合粉压制成圆柱形并磁化，采用制定的烧结工艺在真空烧结炉中烧结。用NIM-10000H磁性能测量装置测试各个样品的磁性能、用高温高压反应釜和CS电化学工作站测试各个样品在湿热和电化学环境中的的耐腐蚀性。通过XRD、SEM、EDS分析手段系统的研究MgO的添加对磁体的晶界相成份、晶界显微组织的影响，找到磁性能与它们之间的内在联系。研究结果表明：适量的MgO掺入可以使NdFeB合金磁性能和耐腐蚀性能在原有的基础上有所提高。添加0.2%MgO时磁体的密度较原来增加了0.527g·cm-3，剩磁较原来增加了0.179T，磁能积增加了74KJ·m-3，过量则会导致磁性能逐渐降低，添加1%、1.2%MgO时磁体出现了烧结不完全现象，有大量微小孔隙。添加0.4%MgO磁体矫顽力最大，矫顽力相比于没有添加MgO的磁体，增加了120KA·m-1。磁体的失重量则与之不同，在腐蚀24h时，未添加MgO的磁体腐蚀失重最小，添加0.2%MgO磁体腐蚀失重最大，腐蚀时间为48h时，添加0.4%MgO的磁体失重量最小，比未添加的磁体降低了6.2mg·cm-2，这说明腐蚀时间的对腐蚀有较大影响。通过XRD分析，添加0.2%MgO的磁体主晶粒(006)晶向晶粒发育良好，晶粒取向度较好。通过SEM观察材料显微组织发现，添加MgO磁体中有新相的生成，对磁畴有强烈的钉扎作用，利于于矫顽力的提高；添加0.4%MgO磁体晶界明朗，有薄层富钕相，主晶粒细化。通过EDS发现添加的MgO仅存在于晶界相当中，没有进入主相，富钕相的氧含量随MgO的添加而逐渐增大，富钕相结构也发生了的转变。适量添加可以细化主相晶粒，防止大晶粒的产生，优化了晶粒生长取向和晶界相，增加了磁粉的湿润性提高了磁体密度，这是材料磁性能增强的主要原因，而过量添加，则会导致相反的效果，如添加1%、1.5%的MgO。通过高温高压加速氧化实验和电化学腐蚀实验，我们用磁体的失重量和电极化曲线的电极位表征磁体的抗腐蚀性，实验数据结果表明，MgO的添加增强了磁体在电化学环境中的耐腐蚀性，，不仅提高了磁腐蚀电位，降低了腐蚀电流密度而且还保护了磁体原有的钝化膜；失重实验也表明适量添加MgO增强了磁体在湿热环境下的抗腐蚀性能，从显微组织观察到磁体的腐蚀坑明显减少，生成了化学性质稳定的化合物，隔断了腐蚀介质的扩散，这对晶界稳定大有裨益。
[Abstract]:NdFeB permanent magnetic materials are applied in every field of our country, from the space engineering of our country to the daily life of people. With the development of more NdFeB functional devices, more commodities will appear around us.China is rich in rare earth resources, NdFeB industry has a good foundation, bright future.However, the independent intellectual property rights of NdFeB industry in China are still relatively small, high-end products fall behind in the United States and Japan, so it is imperative to increase the research on NdFeB industry.The magnets prepared in this paper are sintered in a vacuum sintering furnace, similar to the double alloy method. The composition of the matrix is more than 30 Gd3Al0.8B1.03Fe.In the vacuum glove box, the MgO was mixed with the prepared magnetic powder in different proportions, then the mixed powder was milled by ball mill, then pressed into a cylindrical shape and magnetized. The sintering process was established and sintered in the vacuum sintering furnace.The magnetic properties of each sample were tested by NIM-10000H magnetic property measuring device, and the corrosion resistance of each sample was tested by high temperature and high pressure reactor and CS electrochemical workstation.The effect of the addition of MgO on the grain boundary phase composition and grain boundary microstructure of magnets was systematically studied by means of XRDX SEMS-EDS analysis, and the intrinsic relationship between magnetic properties and them was found.The results show that the magnetic properties and corrosion resistance of NdFeB alloys can be improved by proper addition of MgO.The density of magnets increased 0.527g cm-3, the remanent magnets increased 0.179T, the magnetic energy product increased 74KJ m-3s, and the magnetic properties decreased gradually when the magnets were added with 0.2%MgO. The magnets were not sintered completely and there were a lot of tiny pores when the magnets were added with 0.2%MgO.The coercivity of the magnets added with 0.4%MgO was the largest, and the coercivity was increased by 120KA m -1 compared with the magnets without MgO.The weight loss of magnets is different from that of magnets. When the corrosion time is 24 h, the weight loss of magnets without MgO is the least, and that of magnets added with 0.2%MgO is the largest, and that of magnets added with 0.4%MgO is the smallest when the corrosion time is 48 h.The 6.2mg cm-2 is lower than that of the unadded magnets, which indicates that the corrosion time has a great influence on the corrosion.By XRD analysis, the main grain orientation of the magnets added with 0.2%MgO is well developed and the orientation degree of the grains is better.The microstructure of the material observed by SEM shows that the new phase is formed in the added MgO magnet, which has strong pinning effect on the magnetic domain, which is beneficial to the increase of the coercivity, and the crystal boundary of the added 0.4%MgO magnet is clear, there is a thin layer of neodymium rich phase, and the main grain is fine.It is found by EDS that the added MgO exists only in the grain boundary and does not enter the main phase. The oxygen content of the neodymium rich phase increases with the addition of MgO, and the structure of the neodymium rich phase also changes.The addition of proper amount can refine the main phase grain, prevent the production of large grain, optimize the grain growth orientation and grain boundary phase, increase the wettability of magnetic powder and increase the density of magnets, which is the main reason for the enhancement of the magnetic properties of the material.Will result in the opposite effect, such as adding 1% of MgO 1.5%.Through accelerated oxidation and electrochemical corrosion experiments at high temperature and high pressure, the corrosion resistance of magnets is characterized by the loss of weight of the magnets and the electrode position of the polarization curves.The experimental results show that the addition of MgO enhances the corrosion resistance of magnets in electrochemical environment, not only increases the magnetic corrosion potential, reduces the corrosion current density, but also protects the original passivation film of the magnets.The weightlessness experiment also showed that the proper addition of MgO enhanced the corrosion resistance of magnets in humid and hot environment. From the microstructure, the corrosion pits of the magnets were obviously reduced, resulting in the formation of compounds with stable chemical properties, which separated the diffusion of corrosion media.This is of great benefit to the stability of the grain boundary.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM273

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