烧结Nd-Fe-B磁体晶界扩散TbH2高温稳定性及其机理

采用涂敷方式,在烧结钕铁硼表面均匀涂敷TbH₂粉末,经过不同的扩散温度处理,制备出晶界扩散磁体。研究了晶界扩散TbH₂对烧结Nd-Fe-B磁体常温磁性能及高温稳定性的影响,并分析了磁体矫顽力提升的机理。常温磁性能研究表明,扩散磁体经过890 ℃+490 ℃工艺处理后性能达到最优,矫顽力从1 383 kA/m提升到1 988 kA/m。高温磁性能结果显示,扩散磁体200 ℃的矫顽力温度系数|β|比原始磁体降低0.032%/℃,磁通不可损失hirr比原始磁体降低21.47%,扩散TbH₂明显提高了烧结Nd-Fe-B磁体的热稳定性。分析得出,晶界扩散TbH₂磁体矫顽力提升的机理是Nd₂Fe₁₄B晶粒外延层形成了（Tb, Nd）₂Fe₁₄B核壳结构,提高了磁晶各向异性场;同时改善了磁体的微观组织结构,有效地隔绝了晶粒之间的磁交换耦合作用。      

富铈液相合金添加的再生烧结钕铁硼磁体研究

采用废旧的烧结钕铁硼电机磁钢作为研究对象(牌号33H),研究富铈液相合金添加量对再生烧结钕铁硼磁体的磁性能和微结构的影响。研究结果表明,在相同的烧结温度下,当未添加液相时,再生磁体密度很低;进一步提高烧结温度,磁体密度略有提高,但是磁体容易氧化、甚至开裂。随着液相合金的添加,再生磁体的密度不断提高,磁性能相应地明显改善,这说明液相合金具有明显的助烧结作用。但是当液相合金的添加量超过8%(质量分数)时,再生磁体的矫顽力降低,这可能因为过多的富铈液相添加使磁体中的富稀土相团聚,磁体微观结构变差。当液相合金添加量为5%,烧结温度为1080℃时,再生烧结钕铁硼磁体的磁性能最佳:剩磁Br达到11.67 k Gs,内秉矫顽力Hcj达到18.94 k Oe,磁能积(BH)max为33.1 MGOe。再生磁体的性能与原废旧磁钢相当,甚至略有提高,再生磁体具有优异的退磁曲线方形度(Hk/Hcj=0.972)。     

烧结温度对MM-Fe-B永磁体磁性能与微观结构的影响

利用白云鄂博共伴生混合稀土(MM)制备了MM-Fe-B永磁体,研究了烧结温度对磁性能与微观结构的影响。随着烧结温度的升高,磁体的密度逐渐升高,剩磁、矫顽力、最大磁能积先增大后减小。对比结果:当烧结温度为980℃时,磁性能最优,剩磁0. 862 T(8. 62 k Gs),内禀矫顽力171. 6 k A/m(2. 16 k Oe),最大磁能积84. 6 k J/m3(10. 63 MGOe)。与Nd Fe B最优烧结温度(1060℃)相比MM-Fe-B烧结温度有所降低,有利于节能减排。对磁体微结构分析发现磁体中存在Ce Fe2相,La元素富集于富稀土相中,磁体中存在大量的穿晶畴。探索利用共伴生混合稀土制备永磁体对稀土资源合理高效使用和环境保护具有重大意义。     

(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.      

晶界扩散Dy60Co35Ga5合金对烧结钕铁硼磁体 磁性能及热稳定性的影响

研究了晶界扩散Dy₆₀Co₃₅Ga₅合金对烧结钕铁硼磁体磁性能及其热稳定性的影响.随着扩散温度的升高,磁体的矫顽力（H_cj）呈现出先增加后减少的趋势,并在890 ℃扩散3 h,480 ℃回火5 h的工艺条件下,矫顽力达到较优,从1 209 kA/m提高到1 624 kA/m,磁体的剩磁只有轻微的下降,从1.38 T降低到1.32 T.高温下测试磁体的磁性能,原始磁体和890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的矫顽力都呈下降趋势,但晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的矫顽力在高温下要明显优于原始磁体.原始磁体及890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体在不同温度下保温2 h的不可逆磁通损失分别为63 %和45 %.且DSC结果显示,890 ℃晶界扩散Dy₆₀Co₃₅Ga₅合金磁体的居里温度（T_c）要明显高于原始磁体的居里温度,这表明晶界扩散磁体的热稳定性得到了很大的改善. XRD图谱显示,890 ℃晶界扩散磁体RE₂Fe₁₄B相的衍射峰较原始磁体向右偏移,说明Dy原子及Co原子少部分已进入主相晶粒.      

稀土含量对烧结NdFeB磁体磁性能及力学性能的影响

研究了不同稀土含量的烧结NdFeB磁体的磁性能、微观结构和抗弯强度。结果表明,提高稀土含量可提高烧结NdFeB磁体的抗弯强度,同时对烧结NdFeB磁体的矫顽力和退磁曲线方形度有一定的提高作用,但会降低烧结NdFeB磁体的剩磁。SEM微观形貌图像表明,提高稀土含量可有效改善铸片、烧结NdFeB磁体的微观结构,使富稀土相分布更加均匀连续,从而提高烧结NdFeB磁体的抗弯强度和矫顽力。     

无重稀土烧结Nd-Fe-B磁体的显微结构和磁性能研究

对Ga、Al、Cu和Zr共同掺杂的烧结Nd-Fe-B磁体磁性能和显微结构进行研究，并通过回火工艺对磁体的矫顽力进行调控。结果表明：当一级回火为900℃×150 min,且二级回火为500℃×180 min时，磁体矫顽力H_cj从烧结态的14.33 kOe大幅提高到二级回火态的19.86 kOe,提高了38.6%;方形度H_k/H_cj由0.86增加到0.97;剩磁B_r仅从烧结态13.51 kGs略微下降到二级回火态的13.46 kGs;富稀土相分布更加连续和明显。研究分析表明，矫顽力大幅增加主要是由于含有少量的富Nd相和贫B相的烧结Nd-Fe-B磁体中Ga的掺杂改变了晶界相湿润性，降低了富稀土相中Fe元素的含量。本研究为无重稀土高矫顽力和高剩磁烧结Nd-Fe-B磁体步入产业化夯实了理论基础。     

烧结温度对NdFeB磁体组织与性能的影响

采用速凝薄带加氢破碎法制备了烧结NdFeB永磁体,通过光学显微镜、扫描电镜以及AMT—4磁学特性测量仪表征了磁体的组织和性能,考察了烧结温度对磁体组织和性能的影响规律。结果表明:随着烧结温度的升高,磁体的致密度升高,剩磁、矫顽力、最大磁能积先增大后减小,其原因是随着烧结温度的升高,主晶相晶粒长大,富钕相分布更加均匀;当烧结温度超过某一值时,磁体的组织不均匀,富钕相发生团聚。     

高温2∶17型SmCo永磁体的显微组织及其与磁性能的关系

为了解2∶17型SmCo永磁体的显微组织与磁性能的关系,用粉末冶金法制备了4种Sm(CobalFe0.1-CuyZr0.04)z烧结磁体,每种成分磁体都进行了热处理工艺优化实验;并对磁体的显微组织及其与磁性能的关系进行了研究。结果表明:z值较低,同时Cu含量又较高的Sm(CobalFe0.1Cu0.16Zr0.04)6.7磁体具有最佳磁性能;扫描电镜(SEM)观察表明:显微组织表现为晶粒细小均匀且基本没有孔洞,晶界析出物均匀平滑地沿晶粒边界析出、且不成大块聚集的磁体具有较好的磁性能;磁力显微镜(MFM)观察表明:Sm(CobalFe0.1Cu0.16Zr0.04)6.7磁体的显微组织呈明显的胞状结构,磁畴结构表现为波纹畴结构,其高温磁滞回线在400℃时方形度仍较好,Hci仍有830kA/m,矫顽力温度系数(β)达-0.15%/℃,在500℃时退磁曲线才开始恶化。     

NdFeB磁体的烧结过程研究

研究了在真空和氩气中烧结对NdFeB磁体磁性能和微观组织的影响.结果发现:经真空烧结的磁体磁性能有较大的个体差异,而在氩气中烧结的磁体磁性能则基本均匀一致,与前者相比,其剩磁平均值高0.05～0.09 T,内禀矫顽力要高1.6 MA/m左右,磁能积约高40 kJ/m3.SEM照片显示,在氩气气氛中烧结的磁体的微观组织更加均匀,而经真空烧结的磁体则有较多的缺陷.     

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...     

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnet prepared by warm compaction process

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated in this work. The results show that, both magnetic properties and temperature stability of the bonded magnet can be improved by adding fine SmCoCuFeZr magnetic powder. In the present study, the optimal content of SmCoCuFeZr magnetic powder was about 20 wt.%, in this case, the Br, Hcj, and(BH)maxof the NdFeB/SmCoCuFeZr composite magnet achieved 0.943 T, 1250 kA/m, and168 kJ/m~3, respectively.     

Preparation of Rapidly Quenching （ Nd, Pr ） 12 （ FeCoZr ）82 B6 Alloy and Magnetic Properties of Bonded Magnets

TheanisotropyfieldHAofPr2 Fe14 Bisabout 30 %higherthanthatofNd2 Fe14 Bwhichresultsinhighin trinsiccoercivityfornanocrystallineexchangecoupledcompositepermanentmagnets .SothePr basedisotropicbondedmagnetshavecurrentlyattractedmuchattentions[1～ 4 ] .Howeverthistypeofpermanentmagnethasnotbeenusedinpractice .Thereexistmagneticinteractionsbetweenadja centgrainseitherinnanocrystallinecompositemagnetsorinanassemblyofsinglehardmagneticphaseofrareearth transitionmetalintermetalliccompounds[5～ 8] …     

Rare earth permanent magnets Sm2(Co,Fe,Cu,Zr)17 for high temperature applications

Sintered Sm(CobalFexCu0.1Zr0.03)7.5 (x=0.09-0.21) permanent magnets with higher Fe content were found to have higher remanence Br and maximum energy product (BH)max at room temperature. Br and (BH)max reached maximum of 0.96 T and 176.7 kJ/m3, respectively at room temperature when the Fe content x reached 0.21. However, the intrinsic coercivity Hci at room temperature increased gradually when the Fe content x increased from 0.09 to 0.15, but when x further increased to 0.21, Hci decreased. Hci attained its peak value of 2276.6 kA/m with Fe content x=0.15 at room temperature. For magnets with x=0.15, Br, (BH)max and Hci reached 0.67 T, 81.2 kJ/m3 and 509.4 kA/m at 500℃, respectively, showing good high temperature stability, which could be used in high temperature applications.     

Investigation of Optimal Megnetic Properties in NdFeB Magnets by Artificial Neural Network

In order to study the effect of alloy component on magnetic properties of NdFeB magnets, the experiment schemes are carried out by the uniform design theory, and the relationship between the component and the magnetic properties is established by artificial neural network(ANN) predicting model.The element contents of alloys are optimized by the ANN model.Meanwhile, the influences of mono-factor or multi-factor interaction on alloy magnetic properties are respectively discussed according to the curves ploted by ANN model.Simulation result shows that the predicted and measured results are in good agreement.The relative error is every low, the error is not more than 1.68% for remanence Br, 1.56% for maximal energy product (BH)m, and 7.73% for coercivity Hcj.Hcj can be obviously improved and Br can be reduced by increasing Nd or Zr content.Co and B have advantageous effects on increasing Br and disadvantageous effects on increasing Hcj.Influence of alloying elements on Hcj and Br are inverse, and the interaction among the alloying elements play an important role in the magnetic properties of NdFeB magnets.The ANN prediction model presents a new approach to investigate the nonlinear relationship between the component and the magnetic properties of NdFeB alloys.     

Effects of grain boundary diffusion of PrCu alloy on microstructure and coercivity of hot deformed(Nd,Ce)-Fe-B magnets

The technology of using high abundance rare earth element Ce in permanent magnets has attracted many concerns.In this work,the magnetic properties and microstructures of hot deformed(Nd_(1-x)Ce_x)_(13.8)Fe_(76.1)Co_4 Ga_(0.5)B_(5.6) magnets and a selective magnet treated with PrCu grain boundary diffusion process(GBDP) were investigated systematically.It is found that Ce is beneficial to improving the plastic deformation ability of NdFeB magnets.The strongest c-axis orientation is achieved in the HD magnets with Ce concentration of x=0.3,resulting in good comprehensive magnetic properties of B_r=13.00 kGs,H_(cj)=10.12 kOe,(BH)_(max)=38.42 MGOe.Based on that,the GBDP was implemented on the magnets with the best orientation using Pr_(68)Cu_(32) ribbons and the magnetic properties of B_r=12.87 kGs,H_(cj)=15.65 kOe,(BH)_(max)=37.48 MGOe were obtained.The results of composition distribution and Curie temperature test of the GBDPed magnets illustrate that Pr diffuses into the(Nd,Ce)_2(Fe,Co)_(14)B grains to substitute Ce,which not only improves the Curie temperature of the grains,but also enhances the magnetic performance of the magnets.Through GBDP,the thermal stability of magnets has also been improved.     

Preparation and Properties of Nd-Fe-B/Fe Nanocomposite Magnets

Nd-Fe-B/α-Fe nanocomposite magnets with high magnetic properties were successfully fabricated through a sonochemical process with carbonyl iron as Fe precursor and subsequently SPS. Experimental results show that α-Fe can increase the remanence of Nd-Fe-B/α-Fe nanocomposite magnets while decrease the coercivity. The demagnetizing curve indicates that the hard and the soft phases did not coupled very well, even though the remanence was improved. The magnetic properties of Br 8.61 kGs, Hcj 8.59 kOe and (BH)_max 12.05 MGOe were obtained for Nd-Fe-B/α-Fe nanocomposite magnets with the nominal Fe content of 5 wt.%. It is noted, the exchange coupling was obviously enhanced by a MA process before SPS, and the magnets properties were increased to Br 9.42 kGs and (BH)_max 14.27 MGOe for Nd-Fe-B/α-Fe nanocomposite magnets with the same Fe content.     

Effects of cobalt addition on microstructure and magnetic properties of PrNdFeB/Fe_7Co_3 nanocomposite

The permanent magnetic nanocomposite PrNdFeB/Fe_7Co_3 ribbons were prepared by directly quenching, and the microstructure and magnetic influence of composite materials with Co substitution were studied. The phase identification and the magnetic properties were measured by X-ray diffraction(XRD) and vibrating sample magnetometry(VSM). Microstructure observation was performed using scanning electron microscopy(SEM). The crystallization temperatures of the hard magnetic phase and the soft magnetic phase were measured using differential scanning calorimetry(DSC). The experimental results showed that Co addition improved the Curie temperature of magnets. When the ribbons were melt-spun at 35 m/s, the added content of Co was 4 at.%, and the magnetic properties were the best, which were remanence(Br) of 0.379 T, coercivity(Hci) of 344.4 kA/m, the maximum magnetic energy product(BH)max of 32.6 kJ/m~3. Besides, the activation energy of each phase was calculated by Kissinger equation, which was 310.4 kJ/mol of Fe_7Co_3 phase and 510.2 kJ/mol of 2:14:1 phase, respectively.     

Dependence of Magnetic Properties of Rapidly Quenching （Nd, Pr）x（FeCoZr）94-xB6 Bonded Magnets on Rare Earths Content

By using sub-everquenching and annealing method which has a wide processing window, (Nd, Pr)x(Fe-CoZr)94-xB6(x=12, 10.5, 10, 9) bonded magnets were prepared and the effect of rare earths content on magnetic properties was investigated. Being spun at sub-ove, quenching speed the as-spun ribbons consist of amorphous phases mixed with fine crystallites. After crystallization under optimum annealing conditions and bonded with 3.25%(mass fraction) epoxy, the magnets obtained the optimum magnetic properties. The rare earths content directly determines the magnetic properties. With the reduction of rare earths content, Br increases but Hci and (BH)max decrease, x=10 is the critical value for the magnetic properties change. Below this value, Br increases slowly meanwhile Hci and (BH)max decrease strongly because alloy contains extra fractions of soft magnetic phase which are not coupled with the hard magnetic phase. This experimental result is consistont with the calculated results using the model of volume fraction of soft magnetic phase coupled completely suggested.