【作者】 白书欣；

【导师】 才鸿年；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2006， 博士

【摘要】 粘结NdFeB是在磁学、冶金、复合材料、粉末冶金、化工等多学科知识基础上发展起来的一种新型的功能复合材料,它具有许多烧结磁体所不具备的特点,引起了研究者和企业界的广泛关注。经过近二十年的研究发展,它成为永磁材料家族中的一个新宠,应用范围越来越广。粘结NdFeB的理论和技术主要包括①高性能磁粉的制备、②磁粉与粘结剂预混的配合料制备技术、③磁体的成型技术、④磁体的后处理技术。为了适应不断发展的技术和应用要求,对上述内容进行系统地总结和研究就显得十分必要。作者重点对粘结NdFeB磁体的设计理论、高性能双相纳米交换耦合磁粉、粘结NdFeB磁体用粘结剂和助剂、粘结NdFeB磁体的制备工艺、混杂粘结NdFeB磁体等进行了研究,制备了具有不同特性NdFeB基粘结磁体。本文首先对粘结NdFeB的设计进行了研究,提出了压缩成型和注射成型两类粘结NdFeB的磁粉堆垛模型,计算了这两类磁体粘结剂的最基本需求量,分别为:2.42wt%和5.18wt%;在分析影响粘结NdFeB性能的基础上,提出了其设计流程（图2.5）。在分析总结研究现状的基础上,作者研究了Nd（Pr）-Fe-B-Ti-C系双相纳米耦合磁体,通过电弧熔炼、快淬甩带制备了14种成分的Nd（Pr）₂Fe₁₄B/α-Fe合金,采用VSM测试分析了它们的磁性能,TEM和XRD分析了结构和组成,并对影响其材料结构和性能的因素进行了分析,结果表明:适量的钛和碳加入到Nd（Pr）-Fe-B基双相纳米复合永磁,改变了合金在冷却和晶化退火过程的相析出顺序,使2-14-1相成为先析出相,抑制了α-Fe的析出和晶粒长大,经快淬和晶化退火后,形成了细小均匀Nd₂Fe₁₄B纳米晶粒（20～30nm）被晶界区以α-Fe为主的软磁相所分隔的显微结构;当Re含量为7～9.5at%,Ti与2-14-1相的摩尔比1∶1,TiC与TiB₂的摩尔比1∶2时,Re-Fe-B-Ti-C合金的平均磁能积约为15MGOe（119.4kJ/m³）,其中稀土含量达到9at%时,纳米交换耦合永磁体矫顽力可以达到950kA/m（μ₀H=1.2T）以上。通过对不同粘结剂制备的粘结NdFeB磁体的磁性能、力学性能和磁体制备的工艺性能的实验比较与综合分析,确定了制备压缩粘结NdFeB磁体应选用环氧值高、润滑作用强、对磁粉包裹均匀的固态树脂作为粘结剂的主要成分,其中F48和E-20树脂是理想的树脂;实验研究了配合料存放不同时间后制备的磁体磁性能和力学性能,发现时效性能主要受固化剂与环氧树脂反应难易程度的影响,高温固化剂和潜伏性固化剂适于制备配合料,其中双氰胺/环氧树脂体系制备的配合料综合性能明显优于顺丁烯二酸酐/环氧树脂体系。配合料体系（HQP-2G+F-48+DICY）时效62天内,所制成的磁体抗压强度保持180MPa以上;通过调整尼龙与MOP-D磁粉的比例,混炼了不同配比的尼龙/MQP-D磁粉,热压后制成磁体,测试了磁体的密度,结果表明:78%体积分数的磁粉与尼龙混炼后,当成型压力达到120MPa时,磁体的密度就达到了5.9g/cm³,可以实现低成型压力制备高密度磁体;采用F44树脂和间苯二胺固化剂制成粘结NdFeB磁体在180℃时的强度可以达到110MPa以上,在高温下可以正常使用。本文还对粘结NdFeB磁体制备的关键技术进行了研究,主要研究内容和结果为:（1）通过球磨等手段得到了不同粒度的磁粉,制成粘结磁体后测量其磁性能,并计算出磁粉的性能。结果表明磁粉粒径越小,磁体和磁粉的磁性能就越差,其根本原因是磁粉粒径减小,磁体内部和磁粉颗粒之间退磁场增加导致磁性能变差,如果磁粉的细化过程引起磁粉部分氧化也会导致磁性能的下降。小粒径的磁体制成粘结磁体后,由于磁体密度的下降还会引起磁体性能的进一步下降;（2）实验采用了不同偶联剂、不同用量、和不同处理方法对磁粉进行预处理,通过测量、比较所制备的粘结磁体力学性能与磁性能,认为通过偶联剂溶液对磁粉进行预处理可以明显提高磁粉的磁性能和力学性能,其中硅烷和钛酸酯的最佳用量为1wt%和0.1wt%;（3）实验研究了混胶造粒过程添加不同润滑剂对配合料的流动性和成型性的影响,发现添加0.2%的硬脂酸锌与聚乙烯醇缩丁醛（两者质量比为1∶1）混合润滑剂既可以显著地提高配合料的流动性,又可以保证粘结磁体的力学与磁性能;（4）通过对不同粘结剂含量粘结磁体的磁性能和力学性能测量分析,发现粘结剂的用量为2～3wt%左右时可以得到最佳综合性能;（5）实验通过测定不同压力下磁粉的粒度变化和相应粘结磁体的磁性能,结合磁体断口分析,认为900MPa是适宜的成型压力,成型压力太小磁体密度不高,磁性能低;太大虽然可以进一步提高磁体密度,但磁粉碎化严重,增加了磁体内部的退磁场,磁性能提高并不明显,同时还给成型模具带来严峻的考验;（6）实验研究了不同成型温度下粘结磁体的密度与磁性能,结果表明在树脂软化点以上温度附近进行温压成型可以提高磁体的密度和磁性能;（7）实验采用XRD研究了影响各向异性NdFe₁₂N_x粘结磁体取向度的因素,发现通过溶剂和强磁场预处理可以破坏磁粉之间存在的由于静磁作用而产生的团聚力,再通过磁场中混胶干燥,造粒后磁场成型、固化就可以得到取向度高的磁体,最大磁能积达到了6.44MGOe;（8）实验制备出了最高磁能积为94kJ/m³（11.8MGOe）热固性NdFeB粘结磁体,和密度达到5.9g/cm³、磁能积为62.0 kJ/m³（7.79MGOe）的φ220mm磁体。实验最后研究了各向同性NdFeB和各向异性锶铁氧体、各向异性Sm₂Co₁₇两个体系的混杂粘结磁体,测量了不同的混杂比例的粘结磁体的磁性能,结果表明在NdFeB/锶铁氧体混杂磁体中锶铁氧体含量为50%以下时有矫顽力绝对增大的现象,而在NdFeB/各向异性Sm₂Co₁₇混杂磁体中Sm₂Co₁₇含量为10%时有剩磁增强现象,其磁能积达到了11.3MGOe（89.95kJ/m³）,Henkel曲线表明各向同性NdFeB/各向异性Sm₂Co₁₇混杂粘结磁体中存在有双相纳米耦合永磁中类似的交换作用。混杂磁体同时表现出了较单一磁粉制备的粘结磁体更好的温度稳定性。更多还原

【Abstract】 Bonded NdFeB magnet is a new kind of functional composite materials and is becoming a new subject which is based on magnetism,metallurgy,composite materials, powder metallurgy and chemical engineering etc.Broad attention has been driven to bonded NdFeB magnets because of their special characteristics which sintered NdFeB magnets don’t have.In terms of materials and technics,the routine of bonded magnet includes preparation of high performance magnetic powders,preparation of premixed powders, compressing and the subsequent treatment of bonded magnets.It is necessary to summarized and investgated the above aspects systematically in order to meet the requirements of continuously developing technics and applications.In this dissertation, the design of bonded magnets,high performance nanocomposite exchange-coupled magnetic powder,the binders and curing agents for bonded NdFeB magnets,the technics of preparing bonded NdFeB magnets and bonded hybrid magnets were discussed in detail,and bonded magnets with different characteristics based on NdFeB powders were gained.Two kinds of packing model of magnetic powders for compression moulding magnets and injection moulding magnets were suggested.The least amount of binder for these two kinds of bonded magnets is 2.42wt%and 5.18wt%respectively.The flow chart（Fig.2.5） of designing bonded magnets was given.Nd（Pr）-Fe-B-Ti-C nanocomposite magnets with fourteen different compositions were prepared by means of arc melting and melt-spinning.With the help of Vibrating Sample Magnetometer（VSM）,TEM and XRD,the magnetic properties,microstructure and constituents of these magnets were measured.The factors that influence the microstructure and magnetic properties were also discussed.The results show that the sequence of phase formation in cooling and annealing process is changed for the addition Titanium and Carbon.Addition of Ti and C promotes the formation of 2/14/1 phase and suppresses the formation and the growth ofα-Fe,resulting in a fine microstructure with Nd₂Fe₁₄B（about 20～30nm） surrounded by a boundary phase consisting ofα-Fe and other soft phases.For nanocomposite Re-Fe-B-Ti-C alloys,with 7～9.5at%Rare Eearth metals,ratio of 1:1 for Ti to 2/14/1 phase,ratio of 1:2 TiC to TiB₂,an average energy product could reach to approximately 15MGOe（119.4k J/m³）. Especially when the rare earth metal content reaches 9at%,a high coercive above 950kA/m can be achieved.The magnetic properties,mechanical properties and processing ability of bonded NdFeB magnets with different kinds of binders were well discussed.It was found that solid state resin such as F48 and E-20 was the ideal basis of the binder for their high epoxy value,better lubricative effect and more evenly encapsulating ability of the magnetic powders.The magnetic properties and mechanical properties ot bonded magnets prepared by premixed powders stored for different time were measured.It was found that the aging properties of premixed powders are mainly affected by the reaction activity of curing agent/epoxy resin system.High temperature curing agent and latent curing agent are good candidates for preparing premixed powders due to their stability at room temperature.DICY/epoxy binder shows a better comprehensive performance than maleic anhydride/epoxy binder.After 62 days’ aging,bonded magnets with "HQP-2G powders+F-48 resin+DICY" can get high a compressive strength above 180MPa.Thermoplastic polymer bonded MQP-D magnets were prepared by hot press the premix of MQP-D magnetic powders with different proportion of nylon,and the density of these magnets were measured.The result shows that thermoplastic polymer bonded magnets with a density of 5.9g/cm3 can be gained at the pressure of 120MPa, temperature of 240℃for the magnet with powder volume fraction of 78%,so bonded magnets with a high density can be made at a low pressure.Bonded NdFeB magnets with metaphenylene diamine and F44 resin as a binder has a compressive strength of 110MPa at 180℃,suitable for high temperature application.The key technics for preparing bonded NdFeB were also investigated in this dissertation,the main topics and results were showed as follows.（1） Magnetic powders with various granularities were obtained by mechanical milling and other means.The magnetic properties of bonded magnets using these powders were measured and corresponding properties of these powders were derived. The result shows that the magnetic properties deteriorate when the granularity decrease, and this is due to the increase of demagnetization field between the magnetic particles in the bonded magnets.Furthermore,if partial oxidation of powders occurred in fining process,the magnetic properties also deteriorate.The magnetic properties further decrease because of the low density of bonded magnets with fine magnetic powders.（2） Magnetic powders were pretreated with various coupling agents,different coupling agent quantity and different treatment methods.The magnetic properties and mechanical properties of the bonded magnets prepared by pretreated powders were measured.It was found that pretreatment with coupling agent solution could enhance the magnetic properties and the mechanical properties of bonded magnets magically. The optimal dosage of coupling agent for silicane and titanite is 1wt%and 0.1wt% respectively.（3） The effect of lubricant addition on the fluidity and molding ability of premixed powders were studied.It shows that 0.2wt%addition of the mixture of Zinc Stearate and Polyvinyl Butyral（the weight ratio is 1:1） can increase the fluidity while magnetic properties and mechanical properties staying good at the same time.（4） The magnetic properties and mechanical properties of bonded magnets with different content of binder were measured.Optimal properties could be achieved when the dosage of binder is about 2～3wt%.（5） The dimension of the magnetic powders in bonded magnets and the magnetic properties of the magnets compressed at different pressure were studied.The fracture of bonded magnet was also analyzed.It shows that 900MPa is the most suitable pressure for preparing compression molding bonded magnets.It is impossible to obtain magnets with high density and high magnetic properties if the pressure far below 900 MPa. Increasing the pressure tends to improve the density,but has no use for the magnetic properties because the powders are crushed badly and the demagnetization field between the magnetic particles increases.（6） The density and magnetic properties of bonded magnets compressed at different temperature were measured.The result shows that the density and magnetic properties could be enhanced by hot compressing at the temperature a little higher than the softening point of the resin.（7） The alignment of anisotropic bonded NdFe₁₂N_x magnets was studied with the aid of XRD.It was found that the congregation between the small particles due to the existence of static magnetic field can be eliminated with the combination of solvent processing and being pulse-magnetized.Anisotropic bonded magnets with a good alignment and an energy product of 6.44MGOe was gained.（8） Epoxy bonded NdFeB magnet with the highest energy product of 94kJ/m³ （11.8MGOe） and thermoplastic polymer bonded magnet with diameter of 220mm, density of 5.9g/cm³ and energy product of 62.0 kJ/m³（7.79MGOe） were achieved.At last,two kinds of bonded hybrid magnets,isotropic NdFeB/anisotrpic Sr-ferrite and isotropic NdFeB/anisotrpic Sm₂Co₁₇ were studied in detail.The results show that a coercivity enhancement is found in bonded NdFeB/Sr-ferrite magnets when the mass fraction of Sr-ferrite is below 50wt%.A remarkable remanence enhancement is gained in bonded NdFeB/Sm₂Co₁₇ magnets when the mass fraction of Sm₂Co₁₇ reaches 10wt%, and the energy product of the magnet is 11.3MGOe（89.95kJ/m³）.The Henkel plot of bonded NdFeB/Sm₂Co₁₇ magnets shows that there has exchanging interaction in hybrid bonded NdFeB/Sm₂Co₁₇ magnet when the Sm₂Co₁₇ mass fraction reaches 10wt%, which is the characteristics of nanocomposite exchange-coupled magnets.It is also concluded that bonded hybrid magnets have better temperature stability than that of bonded magnets prepared by one kind of powders.更多还原