放电等离子烧结新型NdFeB永磁材料工艺研究

采用放电等离子烧结技术制备了新型NdFeB磁体，研究了烧结工艺和热处理工艺对磁体的磁特性、尺寸精度及致密度的影响。同时利用B-H回线仪、扫描电子显微镜对其磁特性、显微组织结构进行了分析测试。结果表明，这种新型的烧结NdFeB磁体具有独特的显微组织结构，主相NdFe14B晶粒细小、尺寸均匀，富钕相弥散分布在主相边界上。获得最佳工艺条件下制备的磁体的磁特性为：最大磁能积(BHmax)240kJ／m^3，内禀矫顽力(Hci)1160kA／m，磁体的密度达到7．58g／cm^3，接近材料的理论密度，同时磁体的尺寸精度达到20μm。     

放电等离子烧结NdFeB永磁材料的强韧化

分别采用放电等离子烧结技术(Spark Plasma Sintering,简称SPS技术)和传统烧结技术制备了成分为Nd12.2Pr2Dy2FebalAl1Nb0.3Cu0.2B6的烧结NdFeB永磁体.研究了所制备磁体的冲击韧性和抗弯强度,并利用扫描电镜(SEM)观察了磁体的显微组织形貌.结果表明:SPS技术制备的Nd-FeB永磁体的冲击韧性和抗弯强度较传统烧结磁体有显著提高,前者的冲击韧性与抗弯强度分别为Kc=0.955J/m2、σbb=402.25 Mpa,后者仅为Kc=0.709J/m2、σbb=278.97MPa.显微组织观察发现,SPS NdFeB永磁体的主相晶粒细小均匀、富钕相细小弥散且彼此隔断;断12表现为较明显的解理断裂特征;而传统烧结磁体主相晶粒较粗大、富稀土相粗大且彼此连接,断口呈明显的沿晶断裂特征.     

烧结NdFeB永磁体在HNO3+HF混合溶液中的腐蚀行为

通过SEM,EDS和E-t曲线、Tafel曲线、EIS(交流阻抗谱)对烧结NdFeB合金在HNO3 HF混合溶液中的腐蚀行为及其损伤形貌进行了较系统的研究.结果表明,烧结NdFeB在混酸中的腐蚀是基体相与富钕相的全面腐蚀,腐蚀后晶间富钕相仍呈网状分布于主相晶粒上.     

放电等离子烧结温度对热压/热变形NdFeB纳米晶永磁体磁性能的影响

采用放电等离子烧结技术制备了热压/热变形NdFeB磁体。研究了不同烧结温度对热压磁体、热变形磁体微观结构及磁性能的影响。结果表明,随烧结温度的升高,磁体密度上升,680℃时已达理论密度的99.7%;另一方面,晶粒则随温度的增加发生长大。剩磁和最大磁能积受密度和晶粒大小的交互作用,在650℃时达最大:(BH)m=129kJ/m3,Br=0.87T,Hci=914kA/m。热变形后,磁体主相晶粒的c轴逐渐转向与压力平行的方向,形成磁晶各向异性,使磁体的剩磁和最大磁能积大幅增加。热压烧结温度对热变形磁体的磁性能有着极大影响,其剩磁和最大磁能积随热压温度的升高先升高后降低,620℃热压后,热变形磁体磁性能达最大:(BH)m=339kJ/m3,Br=1.49T,Hci=576kA/m。     

放电等离子烧结NdFeB磁体的烧结特征研究

应用放电等离子烧结技术(SPS)制备新型SPS NdFeB磁体.利用扫描电子显微镜(SEM)观察磁体的显微组织,利用B-H回线仪测量磁体磁性能,利用阿基米德法测量样品密度.系统研究了稀土含量不同的两种NdFeB磁体的烧结特征.结果表明,SPS NdFeB磁体的烧结特征与传统烧结方式的特征不同,且与样品稀土含量密切相关;...     

微观组织调整和稀土含量对烧结NdFeB永磁腐蚀的影响

采用放电等离子烧结技术(SPS)制备了不同稀土含量的新型烧结NdFeB磁体,为了对比,采用传统烧结工艺制备了相同成分的磁体。测量了磁体在高压湿热环境的腐蚀行为。结果表明SPS磁体的耐腐蚀性明显优于传统烧结磁体,而且随着稀土含量的降低,烧结NdFeB磁体的耐腐蚀性能显著提高。     

烧结NdFeB铸造新工艺-薄片铸锭法

合金铸造技术是制备高性能烧结NdFeB磁体的关键工艺之一 .根据高性能磁体制造的设计要求 ,NdFeB合金铸锭微观组织应该具有柱状晶完整 ,没有α -Fe偏析相 ,富钕相弥散分布的特点 .本文比较了现有几种生产中常用的铸造方法 -平板铸造、柱状铸造、薄板铸造等得到的合金铸锭 ,然后介绍了目前国际上高性能NdFeB磁体制备的铸造新工艺 -薄片铸锭法 ,并通过扫描电镜观察了不同Nd含量薄片铸锭的组织结构 .最后展望了薄片铸锭在我国的应用前景 .     

热处理对放电等离子烧结NdFeB永磁材料的影响

采用放电等离子烧结技术(spark plasma sintering,简称SPS)制备了高性能新型NdFeB永磁材料.研究了热处理工艺对SPS NdFeB磁体的组织和性能影响,采用扫描电镜、B-H回线仪研究磁体的显微组织和磁性能.结果表明,不同烧结温度的SPS烧结体对不同温度的热处理表现出同样的规律性,最佳热处理温度为1050℃.SPS NdFeB磁体的热处理过程,富稀土相成分和结构发生改变.在优化工艺条件下制备出最佳性能为Br=1.351T,Hci=674.4kA·m-1,BHm=360.4 kJ·m-3的新型SPS NdFeB磁体.     

W对烧结NdFeB磁体的显微组织和磁性能的影响

主要研究了在烧结ＮｄＦｅＢ磁体的晶界添加Ｗ对显微组织和磁性能的影响，实验结果表明，随Ｗ添加量的增大，晶粒逐渐细化，剩磁稍有下降，面矫顽力逐渐升高，在含Ｗ为１％ｗｔ时，矫顽力达到峰值。扫描电镜的观察显示，加Ｗ磁体在晶界区生成许多杆状相，能谱和Ｘ线射线衍射分析均表明此相为ＷＦｅＢ化合物。     

纯石墨粉对NdFeB烧结磁体的显微组织和磁性能的影响

主要研究了在烧结ＮｄＦｅＢ磁体的晶界添加Ｃ对显微组织和磁性能的影响。实验表明，随Ｃ添加量的增大，晶粒先粗化再细化，矫顽力呈先下降后上升再下降的趋势当Ｃ一达到０．４％ｗｔ时，晶界变得零乱而不规整。Ｘ射线衍射分析表明此时磁体内生成了Ｎｄ２Ｆｅ１７Ｃ相，矫顽力和晶粒尺寸的变化均与Ｎｄ２Ｆｅ１７Ｃ的生成有关。     

New kind of NdFeB magnet prepared by spark plasma sintering

We have produced an anisotropic Nd/sub 15.5/Dy/sub 1.0/Fe/sub 72.7/Co/sub 3.0/B/sub 6.8/Al/sub 1.0/ magnet by the spark plasma sintering (SPS) technique and compared it with a magnet of the same composition processed by the conventional sintering method. We investigated magnetic properties, microstructure, and constituents by a B-H loop-line instrument, a scanning electron microscope, and an energy-dispersive X-ray detector, and studied the effects of processing conditions on the magnetic properties, dimensional precision, and density. We also examined the magnet's electrochemical properties in electrolytes and its corrosion behavior in oxidizing environments. We found that the microstructure of the SPS NdFeB magnet is different from that of the conventional one. In the SPS-processed magnet, the grain size is fine and uniform while the distribution of the Nd-rich phase is heterogeneous. The SPS NdFeB magnet has a maximum energy product of 240 kJ/m/sup 3/ and a coercive force of 1260 kA/m. The density of the magnet reaches 7.58 g/cm/sup 3/, and its dimensional precision is about 20 /spl mu/m. The electrochemical properties and the corrosion resistance of the SPS NdFeB magnet are better than those of the conventional one. The SPS process is a promising method for the production of NdFeB magnets with ideal overall performance.     

Hot deformed anisotropic nanocrystalline NdFeB based magnets prepared from spark plasma sintered melt spun powders

Anisotropic magnets were prepared by spark plasma sintering (SPS) followed by hot deformation (HD) using melt-spun powders as the starting material. Good magnetic properties with the remanence J_r > 1.32 T and maximum of energy product (BH)_max > 303 kJ/m³ have been obtained. The microstructure evolution during HD and its influence on the magnetic properties were investigated. The fine grain zone and coarse grain zone formed in the SPS showed different deformation behaviors. The microstructure also had an important effect on the temperature coefficients of coercivity. A strong domain-wall pinning model was valid to interpret the coercivity mechanism of the HDed magnets. The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. The polarization characteristics of HDed magnets were demonstrated. It was found out that the HDed magnets had better corrosion resistance than the counterpart sintered magnet.     

放电等离子烧结NdFeB磁体的磁化特征

利用放电等离子烧结技术(SPS)制备烧结钕铁硼磁体SPS NdFeB。为了更好地理解SPS Nd-FeB磁体的磁硬化机理,利用振动样品磁强计研究了SPS NdFeB磁体在室温下的磁化和反磁化过程。结果表明,在强度为800kA/m的较低外加磁场和强度为1760kA/m的较高外加磁场下的磁化特征明显不同,前者可称为形核控制模式,后者则为钉扎控制模式。比较样品的磁化过程和反磁化过程的曲线,发现样品的矫顽力大小等于样品磁化过程钉扎场的大小。     

Effect of Heat Treatment on Microstructure and Magnetic Properties of Ce-Doped NdFeB Ribbons

The substitution for Nd by abundant element cerium (Ce) is a practical way for the comprehensive utilization of rare earth resources in NdFeB permanent magnets. In this letter, we have prepared the Ce-doped NdFeB ribbons and conventional NdFeB ribbons by melt quenching method and investigated the effects of heat treatment on the crystallization behavior, microstructure, and magnetic properties of the alloy. The results show that: (1) The crystallization behavior and the microstructural changes of the (Nd,Ce)FeB magnets are similar to the conventional NdFeB magnet when heat treatment. In addition, the Ce₂Fe₁₄B phase has a significant effect on the properties of the whole magnets. (2)The NdFeB phase and CeFeB phase are relatively close to each other after being precipitated from the amorphous phase. The coupling effect between the two phases is strong enough to weaken the effect of the addition of Ce and making the properties of the NdFeB magnets to not reduce too much after adding Ce.     

Properties improvement and structural optimization of sintered NdFeB magnets by non-rare earth compound grain boundary diffusion

Grain boundary diffusion using rare earth (RE)-containing compounds has recently become an effective approach for improving the coercivity and reducing the heavy RE content in sintered NdFeB magnets. Here we report the enhancement of magnetic properties and corrosion resistance of NdFeB magnets by a non-RE compound diffusion process. The Dy-free sintered NdFeB magnets were coated with an MgO layer by magnetron sputtering, followed by solid diffusion heat treatment. With the successful diffusion of MgO into the magnet, the coercivity increasing from 1094 to 1170 kA/m and the maximum energy product increasing from 240 to 261 kJ/m³, together with the enhanced temperature stability and corrosion resistance, have been demonstrated. The underlying mechanisms for these enhancements have been analyzed. Microstructural investigations show that MgO entered mainly into the intergranular regions and modified the composition and structure of the grain boundary phase. The intergranular Nd–O–Fe–Mg phases observed in the MgO diffused magnet contribute to the improved performance. The current non-RE compound grain boundary diffusion process has significance in further minimizing the use of rare earth (RE).     

Effects of sintering conditions on the microstructure and mechanical properties of SiC prepared using powders recovered from kerf loss sludge

The effects of sintering conditions on the microstructure and mechanical properties of the sintered SiC prepared using the SiC powder recovered from the kerf loss sludge were investigated. The recovered SiC powders were consolidated by spark plasma sintering (SPS) and conventional sintering methods. The effects of sintering temperature, time and methods (SPS and conventional sintering) on the phase, grain size and density of SiC were systematically studied. The Vickers hardness of spark plasma-sintered (SPSed) samples was higher than that of conventional sintered samples due to small grain size. When holding time was increased from 10 to 30 min, the grain size and relative density of SPSed samples were also increased, which lead to the almost constant Vickers hardness by competing effects of grain size and relative density. When holding time was over 30 min, no appreciable change of the relative density and grain size were observed, which can lead to similar values of Vickers hardness. SPS process can be used to make SiC with high density and hardness at relatively low temperature compared with the conventional sintering process.     

Comparisons of the Microstructure and Magnetic Properties of Anisotropic NdFeB Magnets Prepared by Hot Pressing and Spark Plasma Sintering

Journal of Superconductivity and Novel Magnetism - NdFeB hot-pressed and hot-deformed magnets were prepared by hot-pressed (HP) sintering and spark plasma sintering (SPS). The effects of sintering...     

Microstructure and properties of Nd-Fe-B magnets prepared by spark plasma sintering

Abstract

Anisotropic Nd₁₅.₅Dy₁.₀Fe_BalCo₃.₀B₆.₈Al₁.₀ magnets were produced by the spark plasma sintering (SPS) technique. The effects of processing conditions on the microstructure, magnetic properties, dimensional precision and density of the magnets were studied. The magnetic properties, microstructure and constituents were investigated by means of a magnetic flux density - magnetic field strength (B-H) loopline instrument, scanning electron microscopy and energy dispersive X-ray analysis. The density of the magnets was determined by the Archimedes method, and the dimensional precision of the magnets was measured by micrometer. It was found that the microstructure of SPS processed Nd-Fe-B magnets is unique; the grain size is fine and uniform while distribution of the neodymium rich phase is heterogeneous. The optimal magnetic properties of SPS processed Nd-Fe-B magnets obtained so far are maximum energy product of 240 kJ m^-3 and coercive force of 1260 kA m^-1. The dimensional precision of the magnets is ~ 20 μm, and the density of the magnets reaches 7.58 g cm^-3.     

Nanocrystalline Nd–Fe–B Anisotropic Magnets by Flash Spark Plasma Sintering

Flash spark plasma sintering (flash SPS) is an attractive method to obtain Nd–Fe–B magnets with anisotropic magnetic properties when starting from melt-spun powders. Compared to the benchmark processing route via hot pressing with subsequent die upsetting, flash SPS promises electroplasticity as an additional deformation mechanism and reduced tool wear, while maximizing magnetic properties by tailoring the microstructure—fully dense and high texture. A detailed parameter study is conducted to understand the influence of Flash SPS parameters on the densification and magnetic properties of commercial MQU-F powder. It is revealed that the presintering conditions and preheating temperature before applying the power pulse play a major role for tailoring grain size and texture in the case of hot deformation via Flash SPS. Detailed microstructure and magnetic domain evaluation disclose the texture enhancement with increasing flash SPS temperature at the expense of coercivity. The best compromise between remanence and coercivity (1.37 T and 1195 kA m⁻¹, respectively) is achieved through a combination of presintering at 500 °C for 120 s and preheating temperature of 600 °C, resulting in a magnet with energy product (BH)_max of 350 kJm⁻³. These findings show the potential of flash SPS to obtain fully dense anisotropic nanocrystalline magnets with high magnetic performance.     

High Performance Sintered NdFeB Magnet

The mass production process of NdFeB magnets with energy≤MGOe and jHc≥ kOe is based on the following technological advancement: (1) effectively controlling oxygen content to less than 2000 ppm. (2) advancement of the melting technology of NdFeB alloy. (3) obtaining of a finer microstructure of the magnet. (4) finding of a new route to enhance the jHc of NdFeB magnets.