钕铁硼晶界重构与高抗蚀性磁体制备研究
发布时间：2018-09-08 15:09
【摘要】：Nd-Fe-B磁体因其优异的磁性能被称为“磁王”,是应用最广泛的稀土功能材料,已成为高新技术的关键基础材料。但是,烧结Nd-Fe-B磁体的晶界富Nd相与硬磁性Nd2Fe14B主相的电位差巨大,导致磁体抗腐蚀性能极差,是目前该领域亟待解决的重要问题。本文针对这一组织结构根源,基于晶界重构思路,设计与合成了Nd64Co36、Nd65Ni35和Nd30Co65Cu5(Nd6Co13Cu)等系列高电位辅合金；采用双合金工艺制备出晶界相电极电位与主相相当的新磁体,有效降低两相间电化学反应的驱动力,显著提高了磁体的本征抗蚀性。此外,采用Ta或Nb等高熔点金属进行晶界改性,可以抑制主相晶粒异常长大,进一步提高磁体的磁性能,尤其是矫顽力。主要结果如下：根据合金相图与元素理化特性参数,设计并合成了Nd64Co36、Nd65Ni35和 Nd6Co13Cu等与主相润湿性良好的低熔点高电位辅合金,进行钕铁硼磁体晶界组织重构。Nd64Co36、Nd65Ni35和Nd6Co13Cu重构晶界合金的熔点分别为566℃、540℃和605℃,低于富Nd相的熔化温度655℃。在烧结过程中先于富Nd相熔化成液态,改善晶界相的流动性和与主相的润湿性,提高了磁体的烧结密度。合金中的Co、Ni和Cu的标准电极电位分别是-0.277 V、-0.250 V和+0.337 V,远高于Nd(-2.431V)和Fe(-0.440 V),进入晶界相后可提高电极电位。此外,Co、Ni、Cu 在晶界处形成化学性质更加稳定的化合物,阻碍腐蚀沿晶界的扩展。由于重构磁体主合金成分非常接近Nd2Fe14B正比相,磁体的总稀土用量可降至28.00 wt.%(仅比正比相高1.33 wt%,远低于商业磁体30.5 wt%的稀土含量),减少了磁体中富Nd相的体积分数,有效提高烧结磁体的抗腐蚀性能,并节约了宝贵的稀土资源,大幅降低成本。通过烧结后续热处理,重构的晶界相沿主相晶粒光滑连续分布,消除相邻铁磁相晶粒间的磁耦合作用,提高磁体的磁性能,尤其是矫顽力。基于双合金工艺,利用上述三种高电位辅合金和近2：14：1正比相的主合金进行晶界重构, 制备出系列高本征抗蚀性Nd-Fe-B烧结磁体。采用(Pr,Nd)12.97Fe80.58Ga0.19B6.26主合金添加0.5 wt.%的Nd64C036辅合金,重构后的磁体综合性能最佳,Br、Hcj和(BH)max分别达到13.99 kGs、13.01 kOe和47.93 MGOe,总稀土含量仅为29.26 wt.%,远低于磁性能相当的N48商用磁体。且该磁体在不同腐蚀环境中都具有更好的本征抗蚀性,在3.5%NaC1溶液中的腐蚀电位为-0.779 V,远高于-1.032 V(N48)；在120℃、2个大气压和100%相对湿度环境下96小时的失重量也从2.47mg/cm2下降到0.3mg/cm2;在0.1 M硫酸溶液中1800秒的放氢量从62 ml下降到35ml。采用Nd65Ni35辅合金进行晶界重构也能提高磁体的本征抗蚀性,其最佳添加量为2wt.%。在此基础上,对稀土含量更低的(Pr,Nd)12.44Fe81.45B6.11磁体进行Nd6Co13Cu三元合金晶界重构。添加量为2wt.%的重构磁体稀土总量仅为28.46wt.%,富Nd相体积分数大幅降低。此外,由于标准电极电位更高的Cu元素的引入,进一步提高了晶界相的稳定性。该磁体在3.5% NaCl溶液中的腐蚀电位提高到-0.705V,在湿热环境下96小时的失重量进一步降低至0.28 mg/cm2;在0.1 MH2SO4溶液中浸蚀1800秒的放氢量也降低至18.52 ml。同时,该磁体仍具有较高的磁性能,其Br、Hcj和(BH)max分别达到14.03kGs、12.62 kOe和48.55 MGOe。基于高熔点金属Ta或Nb进行晶界改性,在提高本征抗蚀性的同时,可以有效抑制主相晶粒异常长大,进一步提高磁体的矫顽力。与商用磁体相比,单独采用Ta进行晶界重构,主相晶粒尺寸由22.4μm细化到8.7μm,磁体矫顽力由16.7 kOe提高至17.7 kOe,湿热环境下96h的失重量由2.47 mg/cm2下降到0.23 mg/cm2。采用Nb和高电位Cu晶界改性,不仅有效细化晶粒尺寸提高矫顽力,更重要的是低熔点高电位元素Cu的共同添加,可以进一步提高晶界电位以及主相与晶界相的润湿性,提高磁体的本征抗蚀性。实验证明,磁体在湿热环境下96h的失重量仅为未改性磁体的1/5；在3.5%NaCl溶液中的腐蚀电位也由-1.115 V提高到-0.799 V,腐蚀电流由62.33μA/cm2降低到12.28μA/cm2。
[Abstract]:Nd-Fe-B magnet is called "magnet king" because of its excellent magnetic properties, which is the most widely used rare earth functional material and has become the key basic material of high and new technology. However, the potential difference between the Nd-rich phase at grain boundary of sintered Nd-Fe-B magnet and the main phase of hard magnetic Nd_2Fe_14B is huge, resulting in the extremely poor corrosion resistance of the magnet, which is an urgent problem to be solved in this field. In this paper, a series of high potential auxiliary alloys Nd64Co36, Nd65Ni35 and Nd30Co65Cu5 (Nd6Co13Cu) were designed and synthesized based on the idea of grain boundary reconstruction, and a new magnet with a grain boundary electrode potential equivalent to the main phase was prepared by double alloy process, which can effectively reduce the driving force of electrochemical reaction between two phases. The intrinsic corrosion resistance of the magnet is improved. In addition, the abnormal grain growth of the main phase can be restrained and the magnetic properties, especially the coercivity, can be further improved by grain boundary modification with high melting point metals such as Ta or Nb. The melting points of Nd64Co36, Nd65Ni35 and Nd6Co13Cu reconstructed grain boundary alloys are 566, 540 and 605, respectively, which are lower than the melting temperatures of Nd-rich phase 655 C. During the sintering process, the Nd-rich phase melts into liquid state before the Nd-rich phase melts, improving the fluidity of grain boundary phase and improving the fluidity of grain boundary phase. The standard electrode potentials of Co, Ni and Cu in the alloy are - 0.277 V, - 0.250 V and + 0.337 V, much higher than those of Nd (- 2.431 V) and Fe (- 0.440 V), respectively. The electrode potentials can be increased after entering the grain boundary phase. The total rare earth content of the reconstructed magnet can be reduced to 28.00 wt. (only 1.33 wt% higher than the proportional phase and much lower than 30.5 wt% of the commercial magnet). The volume fraction of the Nd-rich phase in the reconstructed magnet is reduced, the corrosion resistance of the sintered magnet is improved effectively, and the precious metal is saved. After heat treatment, the reconstructed grain boundary phases are smoothly and continuously distributed along the main phase grains, eliminating the magnetic coupling between adjacent ferromagnetic grains and improving the magnetic properties, especially the coercivity of the magnets. A series of Nd-Fe-B sintered magnets with high intrinsic corrosion resistance were fabricated by grain boundary reconstruction of Au. By adding 0.5 wt.% Nd64C036 auxiliary alloy into (Pr, Nd) 12.97 Fe 80.58 Ga 0.19 B 6.26 main alloy, the comprehensive properties of the reconstructed magnets were the best. Br, Hcj and (BH) Max reached 13.99 kGs, 13.01 kOe and 47.93 MGOe, respectively. The total rare earth content was only 29.26 wt.%, much lower than that of the magnets. The corrosion potential of N48 commercial magnet in 3.5% NaC1 solution is - 0.779 V, which is much higher than - 1.032 V (N48). The weight loss of N48 commercial magnet in 96 hours is also reduced from 2.47 mg/cm2 to 0.3 mg/cm2 at 120 C, 2 atmospheric pressures and 100% relative humidity, and in 0.1 M sulfuric acid solution. The intrinsic corrosion resistance of Nd65Ni35 auxiliary alloy can also be improved by introducing the Nd65Ni35 auxiliary alloy for grain boundary reconstruction. The optimum addition of Nd65Ni35 auxiliary alloy is 2wt. The corrosion potential of the magnet in 3.5% NaCl solution was increased to - 0.705V, and the weight loss was further reduced to 0.28 mg/cm2 in 96 hours under humid and hot conditions, and dissolved in 0.1 MH2SO4. At the same time, the magnetic properties of the magnet are still high. The Br, Hcj and (BH) max of the magnet reach 14.03 kGs, 12.62 kOe and 48.55 MGOe respectively. The modification of grain boundary based on the high melting point metal Ta or Nb can effectively restrain the abnormal grain growth of the main phase and further improve the intrinsic corrosion resistance. Comparing with commercial magnets, the grain size of main phase was refined from 22.4 to 8.7 micron, the coercivity of magnets was increased from 16.7 kOe to 17.7 kOe, and the weight loss was reduced from 2.47 mg/cm2 to 0.23 mg/cm2 in 96 h under hot and humid conditions. The intrinsic corrosion resistance of the magnet can be further improved by the co-addition of low melting point and high potential element Cu, which can further improve the grain boundary potential and the wettability of the main phase and grain boundary phase. Increased to -0.799 V, the corrosion current decreased from 62.33 A/cm2 to 12.28 A/cm2.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM27
本文编号：2230879
[Abstract]:Nd-Fe-B magnet is called "magnet king" because of its excellent magnetic properties, which is the most widely used rare earth functional material and has become the key basic material of high and new technology. However, the potential difference between the Nd-rich phase at grain boundary of sintered Nd-Fe-B magnet and the main phase of hard magnetic Nd_2Fe_14B is huge, resulting in the extremely poor corrosion resistance of the magnet, which is an urgent problem to be solved in this field. In this paper, a series of high potential auxiliary alloys Nd64Co36, Nd65Ni35 and Nd30Co65Cu5 (Nd6Co13Cu) were designed and synthesized based on the idea of grain boundary reconstruction, and a new magnet with a grain boundary electrode potential equivalent to the main phase was prepared by double alloy process, which can effectively reduce the driving force of electrochemical reaction between two phases. The intrinsic corrosion resistance of the magnet is improved. In addition, the abnormal grain growth of the main phase can be restrained and the magnetic properties, especially the coercivity, can be further improved by grain boundary modification with high melting point metals such as Ta or Nb. The melting points of Nd64Co36, Nd65Ni35 and Nd6Co13Cu reconstructed grain boundary alloys are 566, 540 and 605, respectively, which are lower than the melting temperatures of Nd-rich phase 655 C. During the sintering process, the Nd-rich phase melts into liquid state before the Nd-rich phase melts, improving the fluidity of grain boundary phase and improving the fluidity of grain boundary phase. The standard electrode potentials of Co, Ni and Cu in the alloy are - 0.277 V, - 0.250 V and + 0.337 V, much higher than those of Nd (- 2.431 V) and Fe (- 0.440 V), respectively. The electrode potentials can be increased after entering the grain boundary phase. The total rare earth content of the reconstructed magnet can be reduced to 28.00 wt. (only 1.33 wt% higher than the proportional phase and much lower than 30.5 wt% of the commercial magnet). The volume fraction of the Nd-rich phase in the reconstructed magnet is reduced, the corrosion resistance of the sintered magnet is improved effectively, and the precious metal is saved. After heat treatment, the reconstructed grain boundary phases are smoothly and continuously distributed along the main phase grains, eliminating the magnetic coupling between adjacent ferromagnetic grains and improving the magnetic properties, especially the coercivity of the magnets. A series of Nd-Fe-B sintered magnets with high intrinsic corrosion resistance were fabricated by grain boundary reconstruction of Au. By adding 0.5 wt.% Nd64C036 auxiliary alloy into (Pr, Nd) 12.97 Fe 80.58 Ga 0.19 B 6.26 main alloy, the comprehensive properties of the reconstructed magnets were the best. Br, Hcj and (BH) Max reached 13.99 kGs, 13.01 kOe and 47.93 MGOe, respectively. The total rare earth content was only 29.26 wt.%, much lower than that of the magnets. The corrosion potential of N48 commercial magnet in 3.5% NaC1 solution is - 0.779 V, which is much higher than - 1.032 V (N48). The weight loss of N48 commercial magnet in 96 hours is also reduced from 2.47 mg/cm2 to 0.3 mg/cm2 at 120 C, 2 atmospheric pressures and 100% relative humidity, and in 0.1 M sulfuric acid solution. The intrinsic corrosion resistance of Nd65Ni35 auxiliary alloy can also be improved by introducing the Nd65Ni35 auxiliary alloy for grain boundary reconstruction. The optimum addition of Nd65Ni35 auxiliary alloy is 2wt. The corrosion potential of the magnet in 3.5% NaCl solution was increased to - 0.705V, and the weight loss was further reduced to 0.28 mg/cm2 in 96 hours under humid and hot conditions, and dissolved in 0.1 MH2SO4. At the same time, the magnetic properties of the magnet are still high. The Br, Hcj and (BH) max of the magnet reach 14.03 kGs, 12.62 kOe and 48.55 MGOe respectively. The modification of grain boundary based on the high melting point metal Ta or Nb can effectively restrain the abnormal grain growth of the main phase and further improve the intrinsic corrosion resistance. Comparing with commercial magnets, the grain size of main phase was refined from 22.4 to 8.7 micron, the coercivity of magnets was increased from 16.7 kOe to 17.7 kOe, and the weight loss was reduced from 2.47 mg/cm2 to 0.23 mg/cm2 in 96 h under hot and humid conditions. The intrinsic corrosion resistance of the magnet can be further improved by the co-addition of low melting point and high potential element Cu, which can further improve the grain boundary potential and the wettability of the main phase and grain boundary phase. Increased to -0.799 V, the corrosion current decreased from 62.33 A/cm2 to 12.28 A/cm2.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM27
【参考文献】
相关期刊论文 前3条
1 宋振纶;李卫;;钕铁硼永磁材料表面防护技术:特点·应用·问题[J];磁性材料及器件;2008年01期
2 成问好,李卫,李传健;添加Nb对Nd-Fe-B磁体温度稳定性的影响[J];金属学报;2001年01期
3 郑精武;姜力强;陈巧玲;;Electrochemical Corrosion Behavior of Nd-Fe-B Sintered Magnets in Different Acid Solutions[J];Journal of Rare Earths;2006年02期
，本文编号：2230879
本文链接：https://www.wllwen.com/kejilunwen/dianlilw/2230879.html
