Nb的添加对Fe3B/Nd2Fe14B纳米永磁体磁性能与微观结构的影响

研究了微量合金元素Nb的添加对Fe3B／Nd2Fe14B型纳米复合永磁体微观结构与磁性能的影响规律。结果表明,添加Nb元素可以稳定非晶相,阻碍Fe3B粒子的结晶动力学。Nd5．5Fe70．0Co5Cu0．5Nb0．5B18．5非5晶合金在640℃退火处理30min可获得最佳磁性能：Br=1．05T,JHc=367kA／m,(BH)max=80．2kJ／m^3。Nb与Cu的复合添加对Fe3B晶粒的细化效果更显著;Nb元素的添加可以提高合金的磁性能,但添加量必须适中。     

热处理工艺对块体纳米晶Fe3B/Nd2Fe14B复合磁体性能的影响

采用放电等离子烧结技术(Spark Plasma Sintering,简称SPS技术)将快淬Nd4.5Fe77B18.5薄带制备成块状纳米晶复合磁体.着重研究了热处理工艺对磁体密度、微观结构和磁性能的影响.结果表明,通过直接烧结得到的磁体具有超细纳米晶结构,合适的热处理可以消除残余非晶,得到较好的晶体结构和磁性能.但过高的热处理温度和较长的保温时间的增大会造成晶粒长大,结果导致磁性能的恶化.在最佳热处理条件下得到的磁体的磁性能为Br=1.014T,JHc=237.21 kA/m,(BH)max=61.85 kJ/m3.     

Fe3B／Nd2Fe14B双相纳米复合永磁材料研究

纳米复合永磁材料是颇具发展潜力的永磁合金 ,Ｆｅ3Ｂ/Ｎｄ2 Ｆｅ14 Ｂ双相纳米复合永磁材料是其中的主要合金之一。由于其具有优越的性能价格比而倍受关注 ,是替代铁氧体和ＡｌＮｉＣｏ的理想候选永磁材料。制备这类合金的方法一般采用熔体转轮超速激冷法、机械合金法、气体雾化法等 ,其中熔体转轮超速激冷工艺方法是最有效且最常用的方法。实验采用自行研制的生产型真空快淬炉及真空连续晶化炉对Ｆｅ3Ｂ/Ｎｄ2 Ｆｅ14 Ｂ双相纳米复合永磁材料的成分、显微结构及制备工艺进行了研究。确定了性能较好的三元合金成分 ;发现了“厚大片性能更好…     

Nd2Fe14B/(α-Fe,Fe3B)复合纳米晶的生长动力学研究

采用X射线衍射分析(XRD)研究了Fe-Co-Nd-Dy-B非晶合金晶化过程中α-Fe、Fe3B纳米晶的生长动力学.根据纳米晶生长达到稳定状态所需的时间常数tE与退火温度Ta的关系,计算了α-Fe和Fe3B纳米晶的生长激活能为Egα-Fe=95±2 kJ/mol和E Fe3B=133±13 kJ/mol.该值远小于α-Fe和Fe3B两相的表观晶化激活能Ecα-Fe=555 kJ/mol和EcFe3B=481 kJ/mol.这表明Fe-Co-Nd-Dy-B非晶合金晶化过程中α-Fe和Fe3B纳米晶的形成主要由成核所控制.     

α-Fe/Nd2Fe14B复合纳米晶的织构形成研究

采用X射线衍射分析(XRD)技术,研究了NdprFeCoB熔体快淬所制备的α-Fee/Nd2Fe14B纳米晶的织构形成过程.结果表明,Nd2Fe14B纳米晶具有较强的(001)织构,而α-Fe纳米晶具有(110)织构,这些织构垂直于薄带表面,且从自由面到激冷面逐渐减弱.从自由面到激冷面,Nd2Fe14B相在(001)晶面法线方向的尺寸和α-Fe相在(220)晶面法线方向的尺寸逐渐减小.在激冷面各晶面法线方向的尺寸相近,表明纳米晶的形状近似于等轴晶.α-Fe/Nd2Fei4B纳米晶织构的形成和生长受合金薄带在凝固过程中热流梯度的控制.     

快淬Pr2Fe14B粘结磁体制备工艺优化研究

采用过快淬加后续晶化退火处理的方法,研究了快淬速度和晶化工艺对近正分单相快淬Pr2Fe14B粘结磁体磁性能的影响.发现快淬速度、晶化温度和晶化时间均对磁体的组织结构和磁性能有较大影响,以28 m@s-1速度快淬出的条屑,在655℃经10min的晶化处理,可获得最佳磁性能,用3.25wt%环氧树脂粘结的磁体磁性能为:Br=0.69T,Hci=497kA@m-1,Hcb=334kA@m-1,(BH)m=65kJ@m-3.     

合金元素在Nd2Fe14B/α-Fe纳米复合永磁材料中的分布

主要利用三维原子探针研究了Nb和Zr等元素在Nd2Fe14B/α-Fe纳米复合永磁材料中的分布情况。研究发现，Nb、Zr等元素的添加改善了合金的微观结构，使得合金晶化后晶粒细小均匀，晶粒形状更为规则，合金的综合磁性能得到提高。三维原子探针分析结果表明，Nb元素不固溶于Nd2Fe14B硬磁性相，主要以NbFeB的形式在晶界处析出；Zr元素在Nd2Fe14B相内有较高的固溶度，与Nb、Fe在晶界处以成份接近（Zr，Nb）Fe2相的形式析出，富Nb相和富Zr相在晶界的析出阻碍了晶粒的长大，进而细化了晶粒，改善了磁性能。     

Nd2Fe14 B/α-Fe纳米复合永磁材料的有效各向异性

Nd2Fe14B／α-Fe纳米复合永磁材料中存在软-软、软-硬、硬-硬3种不同磁性晶粒界面。不同晶粒间的交换耦合相互作用使其有效各向异性常数Keff减小。Keff可以用这3种不同有效各向异性的统计平均值表示。计算结果显示：如随晶粒尺寸D的减小和软磁性成分的增加而降低。当D减小到4nm时,Keff减小为通常各向异性常数值的1/3∽1/4。当软磁性相体积分数为50％时,Keff的值下降为硬磁性相对应值的1/2左右。有效各二向异性与矫顽力的变化规律基本相同。     

掺杂不同量Nd2O3对CeO2-ZrO2-Al2O3材料性能的影响

采用共沉淀法制备了一系列Nd2O3含量为0～13wt%的CeO2-ZrO2-A12O3(CZA)复合氧化物,并通过X射线衍射(XRD)、低温N2吸附–脱附、氧脉冲吸附(OSC)、H2–程序升温还原(H2-TPR)及扫描电子显微镜(SEM)等方法对所制备的材料进行了表征.研究结果表明,Nd2O3在CZA固溶体中的溶解限约为10wt%,过量Nd的添加会出现分相形成Nd0.5Ce0.5O1.75氧化物.掺杂适量Nd能有效抑制氧化物晶粒的长大,提高材料的热稳定性和氧化还原性能.Nd2O3的掺杂量为10wt%时,样品的织构稳定性最好,1000℃老化5 h后,比表面积和孔容分别达97.14 m2/g和0.44 mL/g.Nd2O3的掺杂量为7wt%时,样品有高的储氧量,经600℃和1000℃焙烧后储氧量分别为938.01μmol/g和821.72μmol/g;体相氧的移动能力最强,还原性能最佳,老化后还原峰温由465℃升高到483℃.SEM结果表明,所制备的材料均为球形颗粒,Nd2O3的添加可以有效阻止高温焙烧过程中粒子的团聚.     

磁性Fe3O4纳米颗粒的可控制备及生长研究

采用热法合成磁性Fe3O4纳米颗粒,通过精细调控实验条件能对其形状和大小进行有效控制。采用X射线衍射仪、透射电镜、振动样品磁强计等对Fe3O4纳米颗粒的成分、形貌及磁性等进行了表征测试。结果表明,Fe3O4纳米颗粒的饱和磁化强度为62.5emu/g。最后探讨了Fe3O4纳米颗粒的合成机理。     

各向异性Nd2Fe14B／α-Fe纳米晶复合磁体的制备和性能

采用声化学法、放电等离子烧结技术(SPS)和热变形工艺制备致密各向同性和各向异性Nd_2Fe_(14)B/αFe复合磁体,研究了软磁相包覆对磁体的结构和性能的影响.结果表明,软磁相α-Fe对各向同性Nd_2Fe_(14)B/α-Fe复合磁体的影响主要表现为增强两相间的交换耦合作用,从而提高剩磁.当α-Fe体积分数的数值适当(不超过2%)时,各向异性Nd_2Fe_(14)B/α-Fe磁体形成较好的c轴晶体织构,具有较高的磁性能.α-Fe体积分数为1%的磁体性能最高:B_r=1.367 T,H_(ci)=712 kA/m,(BH)_m=327 kJ/m~3.     

机械球磨制备纳米双相Nd2Fe14B/α-Fe永磁材料及晶化行为研究

机械球磨氲气保护下的铸态Nd8Fe86B6合金,并进行晶化处理,制备了纳米双相Nd2Fe14B/α-Fe永磁材料.用XRD、TEM和DSC等手段研究了不同球磨工艺和晶化处理工艺对纳米双相Nd8Fe86B6材料组织结构影响.同时研究了非晶态Nd8Fe86B6材料的晶化行为.结果表明延长球磨时间,Nd2Fe14B相迅速细化形成非晶,α-Fe的晶粒尺寸逐渐减小,25h后趋于定值(约为7nm).球磨时间越长,所需完全晶化的温度越高,晶化后粉末的晶粒越小且越均匀.在晶化过程中,非晶态Nd8Fe86B6首先形成Nd4 4Fe77.8B17.8、Nd1.1Fe4B4、Nd2Fe14B和α-Fe四相混合物.升高温度,最后得到Nd2Fe14B相和α-Fe相,但最终产物中仍有少量未分解的Nd1.1Fe4B4相.     

Study of the formation of crystal texture in α-Fe/Nd2Fe14B nanocomposite magnets prepared by controlled melt-spinning

For further improving the magnetic properties of nanocomposite magnets, the study of the formation of crystal textures in the hard magnetic phase is of great significance. In the present study, a strong (00l) crystal texture with the c-axis perpendicular to the ribbon plane was obtained in Nd₂Fe₁₄B nanocrystals in the α-Fe/Nd₂Fe₁₄B nanocomposite magnets prepared by the controlled melt-spinning of NdPrFeCoB. The intensity of the texture weakens from the free surface layer of the ribbon to the layer attached with the wheel. The oriented Nd₂Fe₁₄B crystals have a fine equiaxed characteristic, d = 36 nm, in the layer attached with the wheel and a coarse columnar characteristic, d = 69 nm, in the layer near the free surface. The formation of the crystal texture in the Nd₂Fe₁₄B nanocrystals is attributed to a large temperature gradient normal to the ribbon plane during the melt-spinning process.     

Conditions of formation and magnetic properties of tetragonal Fe14La2B

Tetragonal Fe₁₄La₂B (a = 0.883 nm, c = 1.236 nm)is stable below 860°C. At 25°C it has a magnetization approaching 1.1 T in a field of 2000 kA/m. Its anisotropy field is considerably lower than that of related Fe₁₄Nd₂B or Fe₁₄Pr₂B.     

Micromagnetic simulation on magnetic properties of Nd2Fe14B/α-Fe nanocomposites with Fe nanowires as the soft phase

Fe nanowire array with strong shape anisotropy was employed as the soft phase in Nd–Fe–B based nanocomposites. The effects of the Fe nanowire distribution on magnetic properties of the nanocomposites were investigated by micromagnetic simulation. The results indicate that the shape anisotropy of Fe wires added in the same direction as the uniaxial magnetocrystalline anisotropy of the hard phase cannot increase the coercivity of the nanocomposite. When the nanowires are distributed perpendicular to the easy axis of the hard phase, the shape anisotropy of soft phase can retard the moments from rotating to the full reversed direction, leading to enhanced coercivity. In addition, with increasing the nanowire diameter, the coercivity of the nanocomposite decreases, but the dipolar interaction shows different roles in magnetic reversal of nanocomposite for different distributions of nanowires. The current results suggest that the coercivity of the Nd₂Fe₁₄B/α-Fe nanocomposite can be enhanced by introducing the soft magnetic nanowire array with the diameter less than the exchange length and with the long axis along the direction other than the easy axis of hard phase.     

Magnetic Domain Imaging of Nd2Fe14B Single Crystals With Unmodified Scanning Electron Microscopy

The stray flux manifestations of surface magnetic domains found in as-grown Nd₂Fe₁₄B single crystals were observed by conventional scanning electron microscopy (SEM) without instrumental modifications. Kerr optical microscopy was employed to confirm the results obtained by SEM. Spike domains were observed on the (001) plane, while a lozenge-type domain pattern was observed on (223) plane of Nd₂Fe₁₄B. A modified image-distortion mode was applied to image the three-dimensional stray flux emanating from the sample. The optimum scanning electron microscope imaging conditions are attained with an incident-electron energy set at 5 to 6kV, which produced images with resolution on the order of 1μm. The simplicity of the technique and the ready adaptability of the SEM to such modifications as in situ current and magnetic field application suggest the extension of these to investigations of other materials of technological interest, such as perpendicular media disks.     

Effects of Nd and B contents on the thermal stability of nanocomposite (Nd,Zr)2Fe14B/α-Fe magnets

The effects of Nd and B contents on the microstructure and thermal stability of nanocomposite (Nd,Zr)₂Fe₁₄B/α-Fe magnets have been investigated. It is shown that for Nd_xFe_93−xZr₁B₆ (x = 9–11) alloys, the volume fraction of Nd₂Fe₁₄B increases with increasing Nd content, and the sample with x = 10 exhibits the optimal microstructure and thermal stability. Though the room-temperature _iH_c of Nd₁₁Fe₈₂Zr₁B₆ sample is the highest, it decreases more rapidly than that of Nd₁₀Fe₈₃Zr₁B₆ as temperature increases, indicating the deterioration of the temperature coefficient β. For Nd₁₀Fe_89−yZr₁B_y (y = 5–8) alloys, the remanence and the temperature coefficient α deteriorate with increasing B content. The coercivity and the temperature coefficient β first improve with increasing B content, reaching the optimal values at y = 7, then deteriorate with further increasing B. Coarse grains and the Fe₃B phase are observed in the Nd₁₀Fe₈₁Zr₁B₈ alloy.     

La2Fe14B和Ce2Fe14B合金在快淬和热处理过程中相析出行为的比较

研究了溶体快淬三元La_2Fe_(14)B和Ce_2Fe_(14)B合金的相析出行为和磁性能,对不同快淬速度(10~50 m/s)和不同热处理温度下制备的样品进行了系统分析。结果表明,通过直接快淬,La_2Fe_(14)B合金中不能形成2∶14∶1硬磁相,而Ce_2Fe_(14)B合金可以获得2∶14∶1相。La_2Fe_(14)B合金在10m/s快淬时主要由La和α-Fe相组成,而Ce_2Fe_(14)B合金中2∶14∶1硬磁相在10m/s和20m/s快淬时析出。随着辊速的增加,非晶相逐渐增多并成为主相。在热处理过程中,La_2Fe_(14)B合金析出相以α-Fe和La相为主,并且高温下液态的富La相和α-Fe相可以共存;而Ce_2Fe_(14)B合金中先析出α-Fe,后析出2∶14∶1硬磁相,随后析出相长大。结果还表明,La_2Fe_(14)B比Ce_2Fe_(14)B有更高的非晶居里温度和更低的α-Fe相析出温度。由于硬磁相的析出,Ce_2Fe_(14)B合金可以获得较好的硬磁性能,包括一定的矫顽力。此研究对含La、Ce稀土永磁材料的生产具有一定的指导作用。