【作者】 张修海；

【导师】 熊惟皓；

【作者基本信息】 华中科技大学 ， 材料学， 2008， 博士

【摘要】 本文用模压成型方法制备了粘结Nd-Fe-B磁体，分析了Nd-Fe-B合金体系的热力学性质，利用差热分析仪（DSC）、扫描电镜（SEM）、抗弯／抗压强度测试仪、MATS-2010H永磁材料测量仪等分析设备，系统地研究了硅烷耦联表面改性处理、粘结剂含量、强磁场、成型工艺及固化工艺等参数对粘结Nd-Fe-B磁体组织结构和性能的影响，进而优化了粘结Nd-Fe-B磁体的制各工艺。Nd-Fe-B合金体系的热力学分析表明，在Nd-Fe-B合金体系熔炼及冷却过程中，Nd₂Fe₁₄B相变反应的吉布斯自由能变化小于零，因此，生成Nd₂Fe₁₄B相的相变反应是可以自发进行的，这是制备Nd-Fe-B永磁体的先决条件；元素Nd、Fe和B都是容易被氧化的元素，它们氧化物的生成反应比Nd₂Fe₁₄B相的相变反应更容易，因此，在Nd-Fe-B磁体制备过程中，要尽量降低合金中的氧含量。用硅烷对Nd-Fe-B磁粉进行表面包覆改性处理，改善了磁粉的抗氧化性，提高了粘结磁体的相对密度、力学性能和磁性能，当耦联剂含量为1wt％时，表面处理效果最好。粘结剂含量对磁体性能的影响结果显示：粘结磁体的力学性能随着粘结剂含量的增加而增大；而磁性能随着粘结剂含量的增加而减小。本文研究了环氧树脂粘结Nd-Fe-B磁体制备工艺，工艺C是单向压制成型，且无保压时间，制备工艺简单，生产效率高，工艺C适合大批量工业化生产；工艺C制备磁体时，使磁体获得最佳力学性能的工艺条件为：①环氧树脂与固化剂含量比为7：3，②160℃左右的固化温度，③620Mpa的成型压力；磁体的剩磁和最大磁能积随着成型压力的增加而增加，而内禀矫顽力随着成型压力的增加反而降低。本文用强磁场对环氧树脂粘结Nd-Fe-B磁体进行饱和磁化，当磁场强度从1．5T增到5T时，磁体的剩磁B_r和最大磁能积（BH）_max增加很快；当磁场强度从5T增到10T时，磁体的B_r和（BH）_max增加很慢；当磁场强度大于10T以后，磁体的B_r和（BH）_max几乎不再增加；磁场强度从低到高变化时，磁体的内禀矫顽力H_ci变化不大，没有明显的变化规律。本文利用温压成型工艺制备了酚醛树脂粘结Nd-Fe-B磁体，温压成型磁体的性能比室温压制磁体的性能有较大的提高，在酚醛树脂含量为3wt％，压制压力为620MPa时，室温压制磁体的相对密度仅为89．4％，剩磁为0．6176T，内禀矫顽力为704．2kA／m，最大磁能积为72．1kJ／m³；而温压磁体的相对密度提高到97．3％，剩磁达到了0．6786T，内禀矫顽力达到了714．2kA／m，最大磁能积达到了79．7kJ／m³。酚醛树脂粘结Nd-Fe-B磁体可以不进行二次固化，未二次固化磁体的最佳温压温度为180℃。当其它工艺参数相同时，二次固化后磁体的磁性能与未二次固化磁体的磁性能相比降低了，这是因为二次固化后，磁体的热损失、热应力增大，磁体被氧化的几率增大，导致磁体的磁性能下降，可见二次固化对磁体磁性能是不利的。本文用温压成型工艺制备了尼龙（尼龙12）粘结Nd-Fe-B磁体，160℃温压磁体的力学性能比室温压制磁体的力学性能提高很多，当温压温度从160℃增加到190℃时，磁体力学性能有少量的增加；当温压温度从190℃增加到200℃时，磁体力学性能变化不大；磁体的力学性能随着成型压力的增加而增加，没有出现拐点；磁体的剩磁和最大磁能积随着成型压力的增加而增加，而磁体的内禀矫顽力降低；磁体的磁性能随着固化温度的升高而降低；对环氧树脂粘结Nd-Fe-B磁体及尼龙粘结Nd-Fe-B磁体的断口扫描电镜分析可知，粘结Nd-Fe-B磁体是一种脆性材料，粘结剂的含量及粘结强度是磁体力学性能的决定因素，大颗粒磁粉自身的强度对磁体的力学性能有一定的贡献。本文研究了复合（环氧树脂和尼龙66）粘结Nd-Fe-B磁体，并与环氧树脂和尼龙粘结Nd-Fe-B磁体的性能进行比较，尼龙12粘结剂体系制备Nd-Fe-B磁体由于磁体密度相对较低，磁体内部空隙较多，粘结剂的粘结强度较低，因此，磁体的力学性能也较低；复合粘结剂体系制备Nd-Fe-B磁体，当EP：PA=1．0：3．5时，磁体密度与环氧树脂粘结剂体系的磁体密度相当，但由于尼龙66含量比环氧树脂多2．5wt％，因此，尼龙66是影响磁体粘结强度的主导因素，加上尼龙66的力学性能优于环氧树脂，所以复合粘结磁体的力学性能比其它两种磁体的高。尼龙粘结Nd-Fe-B磁体密度比环氧树脂粘结及复合粘结Nd-Fe-B磁体密度低，磁体内部单位体积中的磁性颗粒少，因此，尼龙粘结Nd-Fe-B磁体的剩磁和磁能积比其它两种磁体的低，但磁体的内禀矫顽力比其它两种磁体的高。更多还原

【Abstract】 Bonded Nd-Fe-B magnets were prepared by the method of compression molding. The thermodynamic properties of Nd-Fe-B alloy system were discussed. The influences of silane coupling treatment, binder content, high magnetic field, compaction process and thermosetting technology on the microstructure and properties of bonded Nd-Fe-B magnets were studied by the analysis of DSC, SEM, bending strength, compressive strength and MATS-2010 Permanent Magnet Test. The preparation process of bonded Nd-Fe-B magnets was optimized.The analysis of thermodynamic properties of Nd-Fe-B alloy system showed that the Gibbs free energy change （AG） in the phase transformation of Nd₂Fe₁₄B phase was less than zero （AGO） during the melting and cooling of Nd-Fe-B alloy. The formation of Nd₂Fe₁₄B phase was feasible in the Nd-Fe-B alloy system, which was the premise condition of preparation of Nd-Fe-B permanent magnet. The elements of Nd, Fe and B were oxidated easily and the formation of their oxides was easier than that of Nd₂Fe₁₄B phase. So reducing the oxygen content of Nd-Fe-B alloy system was significant during the preparation of Nd-Fe-B permanent magnet.The antioxidation, relative density, mechanical properties and magnetic properties of Nd-Fe-B magnets were improved after the silane coupling treatment of Nd-Fe-B magnetic powders. The coupling effect was the best when the content of silane coupling agent was 1wt%. The effects of binder content on the properties of magnets indicated that the mechanical properties of bonded magnets increased with the increase of binder content, but the magnetic properties decreased.The preparation process of epoxy resin bonded Nd-Fe-B magnets had been studied. The technology C was an uniaxial compaction molding, without dwell time, with simple preparation process and high production efficiency, which was suitable for mass production. The mechanical properties of bonded magnets with technology C obtained the best values when the preparation process was in the following:①the proportion between epoxy resin and curing agent was 7:3;②the thermosetting temperature was about 160℃;③the compaction pressure was 620MPa. The B_r and （BH）_max of bonded magnets increased with the increase of compaction pressure, but the H_ci decreased. The epoxy resin bonded Nd-Fe-B magnets were magnetized in high magnetic field. The B_r and （BH）_max increased almost linearly when the magnetic field strength rose from 1.5T to 5T. But the B_r and （BH）max increased slowly when the magnetic field strength exceeded 5T. Moreover, the B_r and （BH）_max increased no longer with increasing magnetic field up to 10T. However, the H_ci kept almost invariably with the magnetic field increasing.The phenolic resin bonded Nd-Fe-B magnets were prepared by the method of warm compaction molding. The magnetic properties of warm compaction magnets were better than that of room compaction magnets. When the phenolic resin content was 3wt% and compaction pressure was 620MPa, the properties of magnets at room temperature were in the following: relative density =89.4%, B_r =0.6176T, H_ci =704.2 kA/m, （BH）_max=72.1kJ/m³; but the properties of magnets at warm compaction were in the following: relative density =97.3%, B_r=0.6786T, H_ci =714.2 kA/m, （BH）_max=79.7kJ/m³. The phenolic resin bonded Nd-Fe-B magnets might have no need for second thermosetting treatment and the best warm compaction temperature was 180℃. The magnetic properties of magnets with second thermosetting treatment decreased because the hot loss, thermal stress and oxidation degree of magnets increased. So the second thermosetting treatment had adverse effects on the magnetic properties of magnets.The nylon （nylon 12） bonded Nd-Fe-B magnets were prepared by the method of warm compaction molding. The mechanical properties of 160℃warm compaction magnets were better than that of room compaction magnets. The mechanical properties of magnets increased a little when the warm compaction temperature rose from 160℃to 190℃. The mechanical properties kept almost invariably when the warm compaction temperature rose from 190℃to 200℃. The mechanical properties increased and had no turning point with the increase of compaction pressure. The B_r and （BH）_max of bonded magnets increased with the increase of compaction pressure, but the H_ci decreased. The magnetic properties decreased with the increase of thermosetting temperature. Scanning Electron Microscopy （SEM） was used to examine the fracture surfaces of epoxy resin and nylon bonded Nd-Fe-B magnets. The bonded Nd-Fe-B magnet was a kind of brittle materials. The binder content and bonding strength were the decisive factors on the mechanical properties of bonded Nd-Fe-B magnets. The strength of the magnetic powder also helped to increase the mechanical properties of magnets a little.The composite bonded （epoxy resin and nylon66） Nd-Fe-B magnets had been studied, whose properties compared with the epoxy resin and nylon 12 bonded Nd-Fe-B magnets. The mechanical properties of nylon 12 bonded Nd-Fe-B magnet were relatively low because of their low densities, many interspaces and low bonding strength. The densities of composite bonded Nd-Fe-B magnets （EP:PA=1.0:3.5） were equivalent to that of epoxy resin bonded Nd-Fe-B magnets. Because the nylon66 content was more 2.5wt% than the epoxy resin content and the mechanical properties of nylon66 were higher than that of epoxy resin, the mechanical properties of composite bonded Nd-Fe-B magnets were higher than that of two other magnets. Because the densities of nylon bonded Nd-Fe-B magnets were lower than that of two other magnets and the magnetic powders in unit volume were less, the B_r and （BH）_max of nylon bonded Nd-Fe-B magnets were lower than that of two other magnets, but the H_ci was higher than that of two other magnets.更多还原