Effect of niobium on thermal stability and impact toughness of Nd-Fe-B magnets with ultra-high intrinsic coercivity

The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.     

Improvement of coercivity and corrosion resistance of Nd-Fe-B sintered magnets by doping aluminium nano-particles

Nd-Fe-B permanent magnets with a small amount of Al nano-particles doping were prepared by conventional sintered method. Effect of Al content on magnetic property, corrosion resistance and oxidation properties of the magnets were studied. Investigation showed that the coercivity rose gradually, while the remanence decreased simultaneously with increase of Al doping amount. Further investigation revealed that most Al element diffused into the main phase and some Al element diffused into the Nd-rich phase. The autoclave test results showed that the corrosion rate of the magnets decreased with Al content increasing. After oxidation, the maximum energy product losses of the magnets with 0.0 wt.% and 0.2 wt.% Al nano-particles doping were 6.13% and 3.99%, respectively. Therefore, Al nano-particles doping was a promising way to enhance the coercivity and corrosion resistance of sintered Nd-Fe-B magnet.     

Al与Mo复合添加对NdFeB磁体矫顽力的影响

本文采用晶间合金化工艺将合金元素Mo和Al直接引入烧结Nd-Fe-B磁体晶间区域,改变晶间区域的合金体系和显微组织,以达到提高磁体矫顽力的目的.实验结果表明Mo在低温时效过程中可抑制晶间富Nd相与主相之间的平衡转变,使晶界区域析出细小二次主相晶粒,使矫顽力提高.     

晶间合金化Ga元素对烧结Nd-Fe-B磁性能与显微组织的影响

用晶间合金化方式直接在(NdPr)29.6(FeCuZr)69.2B1.0粉中加入0.3%Ga(质量分数,以下同),磁体的内禀矫顽力从943.5kA/m提高到1181.0kA/m。分别用晶间合金化方式和传统合金化方式在(Nd-PrDy)30.0(FeCuZr)69.0B1.0中加入0.2%Ga,前者的内禀矫顽力达到1224.0kA/m,远高于后者的971.5kA/m。显微组织结构分析表明:用晶间合金化方式加Ga后改善了边界结构,没加Ga时晶粒边界不平直,晶界处缺陷较多;加Ga后晶界平直光滑,Ga主要分布在晶界,而晶内Ga含量极低。     

晶界扩散Dy–Al–Ga对钕铁硼磁体的磁性能和微观组织的影响

通过晶界扩散Dy₇₀Al₁₀Ga₂₀合金研究了烧结Nd-Fe-B磁体的磁性能和热稳定性能.用NIM-500C高温永磁测量仪和MLA650扫描电镜测出了磁体在扩散前后的磁性能和微观组织的变化.结果表明，在Dy₇₀Al₁₀Ga₂₀合金扩散热处理后，磁体矫顽力从原始的1 080.968 kA/m显著提升到1 671.600 kA/m，提升幅度约为55 %，而剩磁下降很少. Dy、Al、Ga元素在晶界处扩散，很好地隔绝了磁交换作用，提升矫顽力. SEM图显示在扩散Dy₇₀Al₁₀Ga₂₀合金后，可以很明显地看到晶粒外延层有一层灰色的壳层包覆着主相晶粒，很好地起到了隔离晶粒的磁交换作用. XRD显示主相的峰普遍往右偏移，这归因于重稀土元素Dy进入晶粒外延层形成（Nd, Dy）₂Fe₁₄B核壳结构. Dy的原子半径比Nd小，导致峰往右移.      

Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications, the eutectic Tb₈₀Fe₂₀ (wt%) alloy powders were added into the Nd-Fe-B sintered magnets by intergranular method to enhance the coercivity (H_cj) and thermal stability. The microstructure, magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb₈₀Fe₂₀ contents were studied. The experimental results demonstrate that the coercivity (H_cj) of the sintered Nd-Fe-B magnet is significantly enhanced from 14.12 to 27.78 kOe, and the remanence (B_r) decreases not obviously by introducing 4 wt% Tb₈₀Fe₂₀ alloy. Meanwhile, the reversible temperature coefficients of coercivity (β) and remanence (α) of the Nd-Fe-B magnets are increased from ?0.5634%/℃ to ?0.4506%/℃ and ?0.1276%/℃ to ?0.1199%/℃ at 20–170 ℃, respectively. The Curie temperature (T_C) of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb₈₀Fe₂₀ content. Moreover, the irreversible flux magnetic loss (h_irr) is obviously reduced as Tb₈₀Fe₂₀ addition increases. Further analysis of the microstructure reveals that a modified microstructure, i.e. clear and continuous RE-rich grain boundary layer, is acquired in the sintered magnets by introducing Tb₈₀Fe₂₀ alloy. The associated mechanisms on improved coercivity and thermal stability were comprehensively researched.     

Coercivity enhancement mechanism of grain boundary diffused Nd-Fe-B sintered magnets by magnetic domain evolution observation

The grain boundary diffusion(GBD) technology was used to prepare high performance Nd-Fe-B sintered magnets by NdH_3 and TbH_3 nanoparticle diffusion.The factors affecting the coercivity of GBD magnets include distribution of rare earth rich grain boundary phase and substitution of the heavy rare earth.In order to distinguish the influence of various factors on the coercivity,the microstructure and magnetic domain evolution of the original,reference,Nd-diffused,and Tb-diffused magnets were analyzed.The core-shell structure formed by heavy rare earth substitution is the main factor of coercivity enhancement,and it can transform the magnetic domain reversal mode from easy-nucleation(EN) to difficultnucleation(DN).With increasing the diffusion depth,the shell of the core-shell structure gradually becomes thinner,DN grains gradually decrease while the EN grains gradually increase,indicating that the magnetic domain reversal mode is directly related to the core-shell structure.     

Investigation of Coercivity Mechanism for Nd-Fe-B Magnets Prepared by Combination of Strip-Casting with Hydrogen Decrepitation Techniques

The coercivity mechanism of Nd-Fe-B magnets prepared by combination of strip-casting with hydrogen decrepi-tation techniques was investigated. The microstructure of (Nd0.935Dy0.065)14.5Fe79.4B6.1 magnet was observed. The average grain size is about 6 ～ 12 μm. The magnetizing field dependence of the hardmagnetic properties for the (Nd0.935Dy0.065)14.5 Fe79.4B6.1 and the temperature dependence of the coercivity for the Nd14.5Fe79.4B6.1 were investigated. Results show that the coereivity for magnets prepared by the combination of strip-casting with hydrogen decrepitation techniques is controlled by the nucleation mechanism.     

镝扩渗对烧结钕铁硼磁体组织结构与磁性能的影响

对比研究了38UH、42SH和N50薄片状钕铁硼磁体晶界镝扩渗前后的组织结构与磁性能,发现经过镝扩渗处理后磁体的矫顽力提高了400 kA·m-1以上,而剩磁几乎不变,最大磁能积因为矫顽力和方形度的提高而提高。经组织结构分析认为,钕铁硼磁体晶界镝扩渗提高矫顽力主要是通过提高Nd₂Fe₁₄B晶粒外延层的各向异性和形核场实现的。根据Fick第一扩散定律,对磁体晶界镝扩渗进行了模拟计算,可近似得到定温热处理不同时间后渗镝深度及对应的镝的质量浓度及质量分数。      

Optimization of core-shell structure distribution in sintered Nd-Fe-B magnets by titanium addition

In view of the uneven distribution of the core-shell structure of sintered Nd-Fe-B magnets after grain boundary diffusion,this study proposes to use high-melting-point and reactive element titanium(Ti) as an additive to increase the diffusion channels and to enhance the diffusion of heavy rare earth elements along the grain boundary phase.By adding Ti element,the diffusion depth and hence the intrinsic coercivity of magnets are increased significantly.The addition of Ti increases the coercivity ...     

生坯密度对烧结 Nd-Fe-B 磁体结构与性能的影响

结合国内烧结Nd-Fe-B磁体工业生产过程，研究了压制成型时生坯密度变化对烧结Nd—Fe—B磁体致密化程度、显微组织、取向度与磁性能的影响。试验结果表明，生坯密度的提高可促进烧结致密化过程，抑制烧结过程晶粒的不均匀长大，提高取向度，改善磁性能。     

Coercivity enhancement of Ce-Fe-B sintered magnets by low-melting point intergranular additive

Ce-Fe-B sintered magnets with enhanced coercivity were prepared by the powder metallurgy method. The mechanism of the coercivity enhancement in Ce-Fe-B sintered magnets with the low-melting point intergranular additive was discussed in details. It was speculated that the low coercivity of Ce-Fe-B sintered magnet was related to the irregular sharps and relatively low magneto-anisotropy field of the matrix phase. After introducing a 20 wt.% Nd-based intergranular additive, the coercivity markedly increased from 108 Oe to 2560 Oe due to the formation of thin and continuous grain boundary layers and the surface modification of the matrix phase grains. Additionally, the formation of the high anisotropy field(Nd,Ce)_2Fe_(14)B shell was beneficial to the increase of the coercivity as well. This work suggested that adding low-melting point intergranular additives was effective to fabricate the practical Ce-Fe-B sintered magnets.     

Effects of Nd–Ga intergranular addition on microstructure and magnetic properties of heavy-rare-earth-free Nd-Fe-B sintered magnets

In this study, we propose an approach of grain boundary modification that can significantly increase the coercivity of the B-lean Nd-Fe-B sintered magnets by intergranular addition of Nd–Ga. The coercivity is substantially enhanced from 1.51 to 2.04 T through optimizing the microstructure and adjusting the phase composition for the grain boundary phase in the annealed magnets. The matrix grains are covered by a continuous thin grain boundary phase accompanying the formation of intermetallic Nd₆Fe₁₃Ga phases. The analysis of magnetic behaviors above Curie temperature confirms that the grain boundary phase of annealed Nd–Ga doped magnets appears to be non-ferromagnetic, facilitating the intergrain exchange decoupling. Microstructure observation in grain boundary area indicates that some surface of the matrix grain is dissolved in the formation process of the Nd₆Fe₁₃Ga phase. It gives rise to a decrease in the proportion of matrix grains and saturation magnetization of the magnet. The detailed relationship between magnetic properties and microstructure is discussed based on these results.     

Spark Plasma Sintering Nd-Fe-B Permanent Magnets With Good All-Around Property

In present study, sintered Nd-Fe-B permanent magnets with different compositions were fabricated by using both Spark Plasma Sintering (SPS) technique and conventional sintering technique. Microstructure and compositions of both magnets are observed by scanning electron microscope with energy dispersive X-ray detector. Magnetic properties, mechanical properties, and chemical stabilities of both Nd-Fe-B magnets are investigated. Compared with the conventional sintered magnets, SPS Nd-Fe-B magnets possess comparable magnetic properties, better corrosion resistance and mechanical properties. Further investigation shows that the good all-around properties of the SPS magnets result from their unique microstructure. In detail, the grain size of Nd₂Fe₁₄B main phase is fine and uniform, only a few Nd-rich phase forms along the grain boundaries of Nd₂Fe₁₄B, while most of them agglomerates into the triple junctions. As a result, SPS process is expected to be a promising method for the production of new Nd-Fe-B magnets with good all-around properties.     

晶界扩散中Tb对烧结NdFeB磁体微观组织和磁性能的影响

通过晶界扩散技术提升烧结钕铁硼(NdFeB)磁体矫顽力的方法已获得广泛应用,为了研究重稀土磁粉对磁体综合磁性能的影响,本文采用喷涂扩散的方法将重稀土Tb含量为6.0%(质量分数)的磁粉作为复合扩散源的一部分进行晶界扩散并制备了高性能烧结NdFeB磁体。结果表明,当主扩散源占比为60%(质量分数)时,Nd₄₀Tb₆₀对应扩散磁体的矫顽力最高达到21.52 kOe,矫顽力增幅明显。经过微观组织结构和XRD表征分析,重稀土元素Tb沿晶界相扩散进入磁体内部的同时发生了晶格取代反应,可在晶粒表层生成磁晶各向异性场更强的(Nd,Dy/Tb)₂Fe₁₄B硬磁相,显著增强了磁体矫顽力。当主扩散源占比为20%、40%和80%(质量分数)时,Nd₈₀Tb₂₀,Nd₆₀Tb₄₀和Nd₂₀Tb₈₀对应扩散磁体的矫顽力增幅较小,其中Nd₈₀Tb₂₀扩散...     

Effect of aluminum on microstructure and magnetic properties of sintered Nd-Fe-B magnets processed by grain boundary diffusion of Tb-Al

The grain boundary diffusion process(GBDP) of Tb can improve the coercivity of sintered Nd-Fe-B magnets.In this study,the effect of AI on the diffusion of Tb in the GBDP was investigated.The content of diffused Tb-Al was precisely controlled by adjusting the magnetron sputtering process.The Tb equivalent of Al was also studied.Results show that AI promotes the diffusion of Tb deeper into the magnet,reducing the thickness of the shell in the core-shell structure.This study is helpful for further ...     

(Nd,Pr,Ce)-Fe-B磁体的组织与磁学性能

为开发低成本烧结钕铁硼磁体,用30% Ce替代(Nd_0.75Pr_0.25)_32.69Fe_66.25B_1.06磁体中的Nd和Pr,研究了磁体在烧结及回火过程中的组织结构和磁学性能变化.结果表明,取向压坯在1030~1080℃烧结2 h后,随烧结温度升高,磁学性能下降,烧结温度为1030℃时综合磁学性能均最好.烧结态Ce替代磁体的综合磁学性能优于未替代磁体.一级回火后,相组成和晶粒尺寸基本不变,边界结构也未发生明显变化,磁体性能基本不变,或有少量下降.二级回火后,晶界明显改善,获得较清晰且平直的晶界,磁体矫顽力均得到大幅提高.Ce替代磁体的剩磁、矫顽力和磁能积均稍低于未替代磁体.      

Magnetic properties and microstructure of nanocrystalline bulk Nd-Fe-B with Ce-Co addition

The influence of Ce-Co alloy addition and sintering holding time on permanent magnetic properties and micro structure of nanocrystalline Nd-Fe-B bulk alloy were investigated.The coercivity of Nd-Fe-B bulk alloy can be enhanced greatly by more than 100% after adding Ce-Co powders.However,when the concentration of Ce-Co is up to 30 wt%,the density of the magnet can reach the maximum value of 7.58 g/cm~3,but the coercivity does not increase significantly.On the other hand,with the increase of holding time to 10 min,the density and coercivity of magnets increase gradually,reaching up to 7.55 g/cm~3 and 1134.3 kA/m,respectively.After the addition of Ce-Co alloy,Ce-Co may easily diffuse into the Nd-Fe-B matrix during hot-pressing and under the high pressure and temperature,thus increasing the content of grain boundary phase and the pinning effect of grain boundary,which leads to the increase of coercivity.The extension of the hot-pressing holding time may be more conducive to the diffusion of CeCo into the Nd-Fe-B matrix.In addition,the effect of Ce-Co addition on the magnetic properties of Nd-FeB with different content of rare earth was also studied.The addition of Ce-Co can effectively increase the coercivity of nanocomposite Nd_2 Fe_(14)B/α-Fe magnets.The addition of Nb to the parent alloy can further improve the coercivity.For Nd_(11)Fe_(81.5)Nb_1 Ga_(0.5)B_6 alloy with 10 wt% Ce-Co addition,the coercivity can increase from 740.28 to 1098.48 kA/m.     

加剂方式对烧结钕铁硼磁体磁性能的影响

钕铁硼永磁材料在民用、航空航天等众多领域得到广泛的应用.高档次烧结钕铁硼磁体具有良好的市场前景.商业磁体多是由大块烧结毛坯切割而成,磁性能一致性是市场的基本要求之一,润滑剂等化学试剂和磁粉混合不均匀是影响一致性的一个重要因素.钕铁硼磁粉化学性质活泼、容易氧化,制粉的全过程都在氮气气氛下进行,没有合适的设备,想均匀加入化...     

Recycled Nd-Fe-B sintered magnets prepared from sludges by calcium reduction-diffusion process

Environmental friendly recycling process for Nd-Fe-B sintered magnet sludges generated in the manufacturing process, which contain large amount of rare earth, including Nd, Pr and Dy, is badly needed so far. In present study, we have developed an effective route to obtain recycled sintered magnets from Nd-Fe-B sintered magnet sludges by calcium reduction-diffusion (RD) process. Compared to conventional recycling process, our research is focused on recovering most of the useful elements, including Nd, Pr, Dy, Co, and Fe together instead of just rare earth elements. To improve the recycling efficiency and reduce pollution, the co-precipitating parameters were simulated and calculated using MATLAB software. Most of useful elements were recovered by a co-precipitation method, and the obtained composite powders were then directly fabricated as recycled Nd-Fe-B powders by a calcium reduction-diffusion (RD) method. The recovery rates are 98%, 99%, 99%, 93%, and 99%, for Nd, Pr, Dy, Co, and Fe, respectively. The amount of useful elements contained in the recovered composite powders is greater than 99.71 wt%. The process of RD for synthesizing Nd₂Fe₁₄B and subsequently removing CaO was thoroughly investigated. Furthermore, the recycled Nd-Fe-B magnet exhibits a remanence of 1.1 T, a coercivity of 1053 kA/m, and an energy product of 235.6 kJ/m³, respectively, indicating that recycled Nd-Fe-B sintered magnet was successfully recovered from the severely contaminated sludges via an effective recycling route.