Spark Plasma Sintering Bulk Sm2 Fe17NxMagnets

High performance Sm2Fe17Nx magnetic powders were fabricated by ball-milling method and were compacted using spark plasma sintering(SPS) technique.Effects of processing conditions on the magnetic properties and decomposition dynamic of the magnets were investigated.It is found that higher sintering temperature improves the densification of the magnets, while deteriorates their magnetic properties simultaneously due to the decomposition of the Sm2Fe17Nx.Sintering at lower temperature can preserve the crystal structure of Sm2Fe17Nx compound, while the powders cannot be consolidated into a fully dense compact.An increased compressive pressure leads to better magnetic properties and higher density for the magnet at the same sintering temperature.     

Study on bulk Sm2 Fe17 Nx sintered magnets prepared by spark plasma sintering

Abstract

Sm₂Fe₁₇N_x sintered magnets were fabricated by spark plasma sintering (SPS) technique. Effects of sintering pressure, sintering temperature and heating rate on the magnetic properties and crystal structures of the magnets were investigated. The results showed that the density of the magnet was obviously improved with increasing sintering pressure, but the coercivity dropped simultaneously because Sm₂Fe₁₇N_x decomposed into SmN, α-Fe and N₂. The coercivity decreased rapidly when sintering temperature was above 200°C under 1 GPa sintering pressure, which indicated that high pressure promoted the decomposition of Sm₂Fe₁₇N_x even at low temperature. In addition, the decomposition could not be effectively restrained even if the heating rate reached 450°C min^?1.     

Evaluating Acceleration Ability of Electrons of SiO_2 and ZnS in ZnS∶Er Electroluminescence

SinceCoeyandSun[1]discoveredtheinterstitial compoundSm2Fe17Nx,ithasattractedmanyresearch ers′attention.Asakindofpermanentmagneticmate rial,Sm2Fe17Nxexhibitsfairlyhighsaturationmagneti zation(1.54T)[2],highanisotropyfield(14T)under roomtemperatureandhighC…     

Synthesis mechanism of Sm₂Fe₁₇ alloy produced in reduction-diffusion process

Sm2Fe17 alloy was the precursor of Sm2Fe17Nx magnetic materials.Reduction-diffusion(R/D) method was a new preparation process for the Sm2Fe17 alloy,and had been widely employed as a new preparation method for rare earth-transition metal intermetallic compounds.In this text,thermodynamics and kinetics for the synthesis of the Sm2Fe17 alloy by reduction-diffusion(R/D) method in the Ca-Sm2O3-Fe system were analyzed.The related synthesis mechanism of this reaction was investigated in detail by means of scanning electron microscope(SEM).The results showed that the thickness of the Sm2Fe17 alloy layer versus the reaction time could be fit by the parabola law,and its growth model was determined to be:(L0-L)2=43.848 t,the diffusion of Sm into Fe proceeded with the formation of the Sm2Fe17 phase from the very beginning of the reaction,and rich samarium phases,such as SmFe2 and SmFe3,were not formed,and the rate-determining step of the R/D reaction was found to be the peritectic reaction between liquid samarium and solid iron.     

Investigation on mechanism of magnetization reversal for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element methods

Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method. According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed. For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries. However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucleated domain. For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.     

Effect of Interstitial Atom Nitrogen on Properties of RE2Fe17 Compounds

The electronic structure and atomic magnetic moments of clusters NdFe6, NdFe6N3 and Fe8 with a dumbbell atom-pair in rare earth-transition element compounds NdEFe17Nx(x=0, 3) were studied by spin-polarized MS-Xα method. The results are as follows: There are three negative exchange couplings between Fe(c) and Fe(f) atoms in Nd2Fe17, which occur at their odd parity orbitals. Compared to the results of α-Fe calculated by the MS-Xα method, the low Curie temperature of compounds RE2Fe17 can be explained satisfactorily. (2) There is only one weaker negative exchange coupling orbital leaving in between Fe(c) and Fe(f) sites in Nd2Fe17N3. These results may be helpful for understanding the effect of interstitial atom M(M=N, H or C) in Fe2Fe17Mx on Curie temperature. The other key factors affecting the Fe-Fe exchange coupling in Fe2Fe17 compounds were also discussed.     

Preparation of Sm_2Fe_(17)Alloys in Ca-Sm_2O_3-Fe System

Sm2Fe17alloyisanimportantprecursorforthe preparationofSm2Fe17Nxmagnet.Sincethenitrogen containedSm2Fe17(Sm2Fe17Nx)alloy,asapermanent magnetmaterial,possessesahigherCurietempera ture,largeranisotropyfield,betterresistancetooxi dationandthermalstability,and…     

Sm2(Fe,M)17Nx稀土永磁材料的研究进展

综述了Sm2(Fe，M)17Nx永磁材料的最新研究进展，介绍了Sm2(Fe，M)17Nx磁粉及磁体的制备技术，说明用其他元素替换Sm或Fe对材料性能的影响，以及粉末颗粒具有最佳的尺寸和形貌的重要性。并指出放电等离子烧结技术(SPS)有望成为制备Sm2(Fe，M)17Nx致密磁体的一个有效方法。     

纳米晶Fe_3B/Nd_2Fe_(14)B粘结永磁体的磁性能研究

本文研究了粘结剂含量和温度－时间变化对纳米晶Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ粘结永磁材料的磁性能影响。结果表明降低粘结剂含量可显著地提高纳米晶Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ粘结永磁的磁性能；环境温度对纳米晶Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ粘结永磁的磁性能具有重要影响，在较高的温度下其磁性能将显著下降，因此纳米晶Ｆｅ３Ｂ／Ｎｄ２Ｆｅ１４Ｂ粘结永磁只能在较低的温度环境下使用     

A Study of Two-Phase Nanocrystalline Nd_(8.5)Fe_(75)Co_5Cu_1Zr_3Nb_1B_(6.5)Permanent Magnet

Materialswithenhancedremanentmagneticpo larizationwereinitiallypreparedbyCoehoorn[1] frommelt spunNd3.8Fe77B19.2 ribbonsbyheattreatment .Thesimilarbehaviorwasalsoobservedfrommelt spuntwo phasesamplesofNd2 Fe14 Bandα Fe[2 ] .Themag neticpropertiesofisotropicnanocrystallinetwo phasepermanentsdependsensitivelyonmicrostructuralfea tures,suchasdistributionofmagneticallyhardandsoftphases ,meangrainsize ,particleshapeandgrainboundarytype[3] .Inordertoobtainhighmaximumenergyproduct ,itisnecessaryt…     

Crystallization Kinetics of Pr_8Fe_(86-x)Zr_xB_6 Amorphous Alloys

Ｎａｎｏｃｏｍｐｏｓｉｔｅｍａｇｎｅｔｓ ,ｗｈｉｃｈｃｏｎｓｉｓｔｏｆａｔｗｏ ｐｈａｓｅｄｉｓｔｒｉｂｕｔｉｏｎｏｆｈａｒｄ ａｎｄｓｏｆｔ ｍａｇｎｅｔｉｃｇｒａｉｎｓ,ｈａｖｅａｔｔｒａｃｔｅｄｃｏｎｓｉｄｅｒａｂｌｅｉｎｔｅｒｅｓｔｓｓｉｎｃｅｔｈｅｙｃｏｕｌｄ ,ｂｙｅｘｃｈａｎｇｅｃｏｕｐｌｉｎｇ ,ｐｏｔｅｎｔｉａｌｌｙｐｒｏ ｖｉｄｅａｍａｘｉｍｕｍｅｎｅｒｇｙｐｒｏｄｕｃｔ ,(ＢＨ ) ｍａｘ,ｉｎｅｘ ｃｅｓｓｏｆ 10 0ＭＧＯｅ[1] ,ｗｈｉｃｈｉｓｍｕｃｈｌａｒｇｅｒｔｈａｎａｎｙｓｉｎｇｌ…     

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.     

Influence of Zr Additions on Microstructure and Magnetic Properties of Nanocomposite Nd10.5Fe78-xCo5ZrxB6.5 (x=0～5) Alloys

The influence of Zr addition on the microstructure and magnetic properties of nanocomposite Nd10.5Fe78-xCo5ZrxB6.5 (x=0～5) alloys was investigated. It was found that the intrinsic coercivity could be significantly improved by the addition of 2% (atom fraction) Zr. The presence of small amount of amorphous phase is responsible for the low intrinsic coercivity for Zr-free alloy. The small amount addition of Zr may suppress the growth of grains of α-Fe and Nd2Fe14B phases. The more homogeneous microstructure with an average grain size of 20 nm can be obtained for Nd10.5Fe76Co5Zr2B6.5 alloy.     

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.     

Effects of magnetic annealing on crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets

Crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets have been investigated by annealing the as-spun ribbons with magnetic field.The crystallization process was accelerated by field annealing.The hysteresis loop became to be fat by magnetic annealing at 645 oC for 4 min,which was 690 oC for ribbons annealing without magnetic field.The relative content of α-Fe phase was increased from the results of XRD.The strength of the magnetic field had no obvious influence on the remanence and coercivity,but modified the squareness of hysteresis loop.     

Effects of copper and zirconium contents on microstructure and magnetic properties of Sm(Co,Fe,Cu,Zr)_z magnets with high iron content

The evolution of the microstructure,microchemistry and magnetic properties of the Sm(Co_(bal)Fe_(0.28)-Cu_yZr_x)_(7.6) magnets with different Zr and Cu contents was investigated.It is found that the coercivity of the Sm(Co,Fe,Cu,Zr)_z magnets is sensitive to Zr content.The deficiency of Zr content causes heterogeneity of Cu and Fe distributions,while an excessive Zr content leads to the formation of a SmCoZr impurity phase.The cellular structure and distribution of Cu concentration.gradient between the cell boundary phase and cell pha se are destroyed by inappropriate Zr content,which results in a reduction of coercivity.The Cu concentration difference between the cell boundary phase and cell phase increases with increasing Cu content.The coercivity of the Sm(Co_(bal)Fe_(0.28)Cu_yZr_(0.02))_(7.6) magnets increases from 10.4 to 25.4 kOe for y=0.05 and y=0.07.However,the excess of Cu element destroys the cell boundary phase and enlarges the cell size,resulting in a significant decrease of squareness and energy density.The optimum performance(remanence of 11.4 kG,coercivity of 2 5.4 kOe,maximum magnetic ene rgy product of 30.4 MGOe) was obtained for the Sm(Co_(0.63)Fe_(0.28)Cu_(0.07)Zr_(0.02))_(7.6) magnet.     

Morphology and magnetic properties of Sm2Co7/α-Fe nanocomposite magnets produced by high energy ball milling and spark plasma sintering

In this article,the Sm₂Co₇/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30 wt% α-Fe was added into Sm₂Co₇ matrix without the decrease of remanence.Optimal energy product(BH)max of 9.2 MGOe was obtained with 20 wt% α-Fe.TEM observation shows that the grain size of α-Fe is 20-50 nm which ensures a good coupling effect between soft and hard phase.One more thing needs to be mentioned is that there exists inter-diffusion between Sm-Co phase and α-Fe phase.Moreover,our results can also illustrate that the Sm₂Co₇/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo₅/α-Fe magnets prepared by the same process due to the large domain width of Sm₂Co₇ phase.     

Coercivity enhancement of Nd2Fe14B/α-Fe nanocomposite magnets through neodymium diffusion under annealing

The coercivity enhancement of ball-milled Nd2Fe14B/α-Fe nanocomposite magnets was investigated. It was found that the coercivity could be enhanced through mixing a small amount of Nd powder with as-milled Fe-rich Nd-Fe-B powders. The annealed samples were investigated by means of X-ray diffraction, scanning electron microscopy and magnetic measurement systems. Under annealing, some of Nd powders promoted the formation of hard magnetic phase Nd2Fe14B. On the other hand, a few of Nd would diffuse into the interface of Nd2Fe14B/α-Fe nanocomposite to compensate for the loss of the interfacial magnetic anisotropy. These two features are all beneficial to the coercivity.     

Sintering and magnetocaloric properties of gas atomised LaFe11.0Si1.2Co0.8

ABSTRACT

The sintering behaviour of LaFe_11.0Si_1.2Co_0.8 powder produced by gas atomisation was examined to provide a basis for the application of powder metallurgical shaping technologies to magnetocaloric La(Fe,Si)₁₃-alloys. The aim was to establish sintering parameters for attaining both high densification and good magnetocaloric properties for the investigated particle sizes <10 µm and <25?µm. Dilatometry measurements and sintering trials were carried out and density, microstructure and entropy change ΔS of the sintered samples were analysed. For the fine particles <10?µm, the lowest investigated sintering temperature 1150°C results in a relative density of 97%, a low α-Fe content and a high ΔS?=??5?J?kg^?1?K^?1 (ΔH=2?T). For powder <25?µm, a two-stage process is required to achieve similar properties.     

Magnetic Microstructures of 2:17 Type Sm(Co,Fe,Cu,Zr)z Magnets Detected by Magnetic Force Microscopy

The magnetic microstructures of 2:17 type Sm(Co,Fe,Cu,Zr)z magnets were detected by magnetic force microscopy.Comparing the microstructures of the specimens coated with and without Ta thin film before and after heat-treatment, it is found that: (a) as a protection layer, Ta coating layer about 20 nm thick can effectively restrain Sm volatilization under high temperature;(b) the stress built in the 2:17 type Sm-Co magnets during specimen preparation only affects some local parts of the domain structures;(c) the magnetic microstructures vary largely for specimens heat-treated at high temperature without Ta film coating due to Sm volatilization.In addition, by comparing with high coercivity Fe-Pt point tips, it is found that the Co-Cr thin-film tips are not suitable for detecting the magnetic microstructures of strong permanent magnets.