【作者】 崔雪鸿；

【导师】 曾德长；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2012， 博士

【摘要】 纳米晶双相复合永磁材料是由饱和磁化强度高的软磁性相和各向异性场强的硬磁性相在纳米尺度通过交换耦合相互作用而形成的倍受关注的新型永磁材料。这类材料具有稀土含量低，价格便宜，化学稳定性好等特点，具有潜在的开发应用前景。本文采用熔体快淬以及铜模水冷吸铸法制备出了纳米复合REFeB/Fe3B永磁材料，同时系统地研究了其组织结构与磁性能关系以及反磁化机制。采用熔体快淬方法制备15m/s快淬速度的REFeCoBM薄带，对于NdFeCoBM体系，直接快淬成份Nd₉Fe_71.5B_15.5Zr₄薄带矫顽力为891kA/m，剩余磁极化强度为0.77T，饱和磁极化强度为1.37T，Jr/Js=0.56，最大磁能积为82.9kJ/m³，添加元素提高了薄带退火后的综合磁性能。而Co和难熔金属的复合添加使薄带在15m/s的转速下得到了完全非晶，验证了Co和难熔金属的复合添加可以提高体系非晶形成能力。对于Pr_9.5（FeCo）_71.5B₁₅M₄体系，薄带出现了二元相Fe₂B和软磁性相Fe₃B，15m/s的快淬速度没能得到非晶或者直接快淬硬磁性相薄带。采用熔体快淬方法制备50m/s快淬速度的REFeCoBM薄带。对于Nd（FeCo）BM（Nb,Zr）体系，Nb和Zr的添加能提高合金的非晶形成能力，而且能改善快淬薄带晶化后的矫顽力和综合磁性能。同时Nb添加比Zr添加更能细化退火薄带的晶粒，改善微结构和磁性能。虽然Co的添加对矫顽力有所降低，但却能提高退火薄带的剩余磁极化强度温度稳定性、合金的剩余磁极化强度，及最大磁能积。9%的Nd体系中Nd₂Fe₁₄B硬磁性相比9.5%的Nd的体系中少，因此，9%的Nd体系的矫顽力较9.5%的Nd体系小。根据实验数据与理论分析了矫顽力机制。并且进一步分析了合金中相互作用关系的Henkel曲线，证实了合金中确实存在交换耦合作用。分析了Pr_9.5（FeCo）_71.5B₁₅M（Nb, Zr）₄成份的结构与磁性能， Pr取代Nd降低了薄带晶化峰的峰值温度，说明Pr加入使合金热力学稳定性变差，晶化转变及晶粒长大易于进行，从而使合金的显微结构比较粗大。对于DyFeBM（Nb, Zr）体系，Dy₂F₁₄B的高磁晶各向异性场给合金带来了高矫顽力，但是，由于它本身的饱和磁化强度就很低，而且它的交换长度较短，对软磁性相的分布和尺寸有更高的要求，很难达到充分的交换耦合，导致剩磁与最大磁能积都很低。用铜模水冷吸铸的方法制备成分（Y, Dy, Nd）₄FeB₂₂（Ta, Nb）₂直径2mm的棒材合金，成分Dy₄Fe₇₂B₂₂Nb₂得到了完全非晶的2mm棒材样品。分析了形成大块非晶可能的原因。同时采用单辊甩带法制备了相同成分的50m/s快淬薄带，通过热分析，利用基辛格方程计算了Dy₄Fe₇₂B₂₂Nb₂体系的晶化激活能。两个晶化放热峰的晶化激活能分别为572和484kJ/mol。两个放热峰分别对应Fe₃B和Dy₂Fe₁₄B。对棒材和热处理后的薄带样品进行了磁性能测试可知，由于其体系中稀土成份很低，导致了硬磁相Dy₂Fe₁₄B的相成份也很低，因而矫顽力较小，永磁性能不高。采用铜模水冷吸铸制备了（Nd, Pr）（Fe, Co）B（Nb, Zr）直径为2mm以及1mm的棒材。在Nd（Fe, Co）B（Nb, Zr）系列中，主要的相结构为硬磁性相Nd2Fe14B和软磁性相（Fe₃B,Fe）。成份Nd₉Fe_71.5B_15.5Nb₄直接快淬吸铸棒材剩磁为0.56T，矫顽力为568kA/m，最大磁能积为35.9kJ/m³。在650oC，10分钟退火后，矫顽力高达1151kA/m，剩余磁极化强度也略有增加。其原因可能在于二元相FeNb的存在，FeNb相弥散于Nd₂Fe₁₄B相中，提高了畴壁之间的钉扎，同时又保留了软硬磁性相之间的强交换耦合作用。在Pr（Fe,Co）B（Nb, Zr）系列中，主要的相结构为硬磁性相Pr₂Fe₁₄B和软磁性相（Fe₃B, Fe）。直接吸铸棒材的矫顽力在40-159kA/m之间。成份Pr_9.5Fe_51.5Co₂₀B₁₅Nb₄在650oC保温退火5分钟，退火后的矫顽力高达1210kA/m，剩余磁极化强度为0.61T,最大磁能积为65.1kJ/m³。二元相Fe₂Nb在磁体畴壁之间的钉扎作用，有效地抑制了磁矩反转。对于（Nd, Pr）（Fe, Co）B（Nb, Zr）1mm直接吸铸棒材，成份Nd₉Fe_71.5B_15.5Nb₄表现出较好的硬磁性能，矫顽力为307kA/m，剩余磁极化强度为0.57T，最大磁能积为34.8kJ/m³。而Pr系列中，Pr_9.5Fe_71.5B₁₅Nb₄矫顽力为1113kA/m，剩余磁极化强度为0.61T，最大磁能积为56.2kJ/m³。Pr_9.5Fe_71.5B₁₅Zr₄矫顽力为1118kA/m，剩余磁极化强度为0.69T，最大磁能积为80.7kJ/m³。更多还原

【Abstract】 Nanocomposite permanent magnetic material is a kind of attracting new permanentmagnet. It consists of both nano-scale hard magnetic phase with high anisotropic field andsoft magnetic phase with large saturation magnetization, leading to excellent magneticperformance through exchange coupling between their neighboring atomic magnetic moments.In addition to the high maximum energy product that may be achieved, nanocompositemagnets are of commercial interest because they require less of an expensive rare earthelement, low cost and high corrosion resistance.In this dissertation, nanocomposite REFeB/Fe3B type hard magnetic alloys have beenprepared by melt-spinning technique with subsequent crystallization annealing and coppermold water cooling method. The microstructure and magnetic properties of the alloys havebeen investigated. The magnetization and demagnetization behavior of nanocomposite alloyshave also been studied.REFeCoBM ribbons were fabricated by single copper rolling at speed of15m/s. In theNdFeCoBM alloys, for Nd₉Fe_71.5B_15.5Zr₄component, amazing magnetic properties ofjHc=891kA/m, J_r=0.77T, J_s=1.37T, J_r/J_s=0.56, and （BH）_max=82.9kJ/m³were achieved for as-spunalloy ribbons. The doping of Co and refractory elements such as Nb, Zr enhances the GFA（Glass Forming Ability） to get fully amorphous ribbons, and also improves the magneticproperties after heat-treatment. For Pr_9.5（FeCo）_71.5B₁₅M₄alloys, fully amorphous or hardmagnetic properties failed in as--spun ribbons. The binary Fe2B phase and soft magneticphase Fe₃B were exhibited in ribbons.REFeCoBM ribbons were fabricated by single copper rolling at speed of50m/s. InNd（FeCo）BM（Nb, Zr） alloys, the addition of Nb and Zr can enhance the GFA, refine thestructure after annealing and improve magnetic properties. The addition of Co can enhancethe Jrand the temperature stability of Jr, still improve the maximum magnetic energy productat the expense of slightly coercivity decreasing. The contents of9.5at%Nd have highercoercivity than the9at%, due to the increasing of hard magnetic phase Nd2Fe14B. Thecoercivity mechanism was analyzied based on experiments and theory. Furthermore, thehenkel plots were analyzed to testify the exchange coupling in alloys. The structure andmagnetic properties of Pr_9.5（FeCo）_71.5B₁₅M（Nb, Zr）₄were also studied. With the substitutionof Nb by Pr the alloy has a lower crystallization temperature, which means that Pr makes thealloy instabler in crystallization kinetics. So the crystallization transition and the grain growthtake place easier, which results in coarse and inhomogeneous microstructure and a lower remanence. For DyFeBM（Nb, Zr） alloys, the high anisotropic field of Dy₂Fe₁₄B brings in highcoercivity, due to its low saturation magnetization and short exchange length, improves therequirement of the distribution of soft magnetic phase and grain size, which are hard to getfully exchange coupling, then leads to lower remanence and less maximum energy product.（Y, Dy, Nd）₄FeB₂₂（Ta, Nb）₂alloys of2mm diameter rod were prepared by a coppersuction casting method in water cooled crucible. Dy₄Fe₇₂B₂₂Nb₂was fully amorphous by theXRD test in the core of the rod. The reason of the bulk metal glass （BMG） forming wasanalyzed by Senkov principle and Inoue empirical rules. Meanwhile, the50m/s as-spunribbons of same components were fabricated, and the crystallization activation energy ofDy₄Fe₇₂B₂₂Nb₂was calculated by thermal analysis and Kissinger equation. The crystallizationactivation energy of two exothermal peaks were572and484kJ/mol, corresponding to Fe3Band Dy₂Fe₁₄B, separately. The magnetic propertied of as-cast rod and annealed ribbons weremeasured; the coercivity was low, due to low rare earth and Dy2Fe14B phase.（Nd, Pr）（Fe, Co）B（Nb, Zr） alloys of2mm and1mm diameter rod were prepared by acopper suction casting method in water cooled crucible. The Nd（Fe, Co）B（Nb, Zr） alloysmainly consist of hard magnetic phase Nd₂Fe₁₄B and soft magnetic phase （Fe₃B, Fe）. Themagnetic properties of ofjHc=568kA/m, J_r=0.56T, and （BH）max=35.9kJ/m³are achieved forNd₉Fe_71.5B（15.5）Nb₄as-cast2mm rod. After annealed at650oC for10minutes, the coercivityreaches up to1151kA/m, and the remanence also has slight increase. It attributes to theexistence of binary phase FeNb. The FeNb particles distributing in the grains hold the reversedomains wall and meanwhile preserve the strong exchange coupling between soft and hardmagnetic phases. The Pr（Fe, Co） B（Nb, Zr） alloys mainly consist of hard magnetic phasePr2Fe14B and soft magnetic phase （Fe₃B, Fe）. The value of coercivity is between40-159kA/mfor as-cast rod samples. After annealed at650oC for5minutes, the magnetic properties ofPr_9.5Fe_51.5Co₂₀B₁₅Nb₄isjHcof1210kA/m, Jrof0.61T,（BH）maxof65.1kJ/m³. The Fe₂Nbparticles pin the domain walls and hinder the reverse domains from growing and moving.For （Nd, Pr）（Fe, Co）B（Nb, Zr） as-cast rods of1mm diameter, the component ofNd₉Fe_71.5B_15.5Nb₄shows the best hard magnetic properties, i.e.jHc=307kA/m, Jr=0.57T,（BH）max=34.8kJ/m³. In Pr series, The magnetic properties of Pr_9.5Fe（71.5）B₁₅Nb₄isjHcof1113kA/m, Jrof0.61T and （BH）maxof56.2kJ/m³, and Pr_9.5Fe_71.5B₁₅Zr₄isjHcof1118kA/m, Jrof0.69T and （BH）maxof80.7kJ/m³.更多还原