Effects of grain boundary ternary alloy doping on corrosion resistance of(Ce,Pr,Nd)-Fe-B permanent magnets

To satisfy the application of different environments,grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance.In this paper,the alloys were prepared by mixing different ratios of the master alloy(Ce,Pr,Nd)-Fe-B and the sintering aid(Pr,Nd)-Al.The coercivity of sintered(Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt%of(Pr,Nd)-Al,while the maximum energy product decreases slightly.We systematically investigated the corrosion behavior and micro structure of the sintered magnets in order to determine the mechanism of the degradation.The sintered(Ce,Pr,Nd)-Fe-B magnets with 2 wt% of(Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others,due to the distribution of intergranular phases.The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al,improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd,Pr or Ce.In addition,the element distribution of the magnets doped by(Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability.Therefo re,intergranular adding te rnary(Pr,Nd)-Al alloy powders results in both high coe rcivity and good corrosion resistance synchronously.     

Abnormal corrosion behavior of dual-main phase sintered(Ce,Nd)-Fe-B magnets in different sodium solutions

Sintered(Ce,Nd)-Fe-B magnets with high cost performance were prepared by substituting of Ce for Nd with the dual-main phase method.The corrosion behaviors of dual-main phase sintered(Ce_xNd_(1-x))_(30)Fe_(69)B_1(x=0.15 wt%,0.3 wt%) magnets,which were named as Ce15 and Ce30,were studied in 3.5 wt% NaCl,6.6 wt% Na_2 SO_4 and 3.0 wt% NaOH aqueous solutions,respectively.The galvanic corrosion of Ce30 is stronger than that of Ce15.However,the mass loss value of Ce30 is smaller than Ce15 after free corrosion for 33 d in NaCl solution.In the other two solutions,all the results show that the corrosion resistance of Ce30 is better than that of Ce15.The scanning electron microscope results show that the crack and shedding of the magnetic phase of Ce30 is less than that of Ce15.Combined above,the abnormal corrosion behavior shows that Ce30 magnets perform better corrosion resistance than Ce15,and the degradation degree of magnetic phase mainly affects the corrosion resistance of magnets.     

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.     

Magnetic properties and microstructures of terbium coated and grain boundary diffusion treated sintered Nd-Fe-B magnets by magnetron sputtering

Tb coating on the surface of commercial sintered Nd-Fe-B magnet was prepared by DC magnetron sputtering.The secondary heat treatment was used to regulate the microstructure for the enhancement of coercivity,namely diffusion treatment and annealing treatment.The coercivity increases significantly from 18.3 to 28.0 kOe,the remanence decreases slightly from 14.1 to 14.0 kGs,and the comprehensive magnetic properties are higher than 75(Hcj+(BH)_max=76.7).SEM results indicate that,on the one hand,950℃is the optimal diffusion temperature.Lower diffusion temperature results in insufficient diffusion of Tb element.Higher diffusion temperature can lead to the main phase grain growth,the decrease of Nd-rich phase,and forming holes in the magnet.On the other hand,500℃is the optimal annealing temperature.Lower annealing temperature can result in the reduction of Nd-rich phase.Higher annealing temperature can generate the non-defined Nd-rich thin layer between grains.     

Corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets

(Ho,Nd)FeB magnets with different Ho contents were prepared by Ho substitution for part of Nd during the casting process. Effects of Ho contents on the corrosion resistance and mechanical properties of (Ho,Nd)FeB magnets were analyzed by a highly accelerated aging tester, an electrochemical workstation, a microhardness tester, a bending tester, a scanning electron microscope and an X-ray diffractometer. Results show that the addition of Ho can change the main phase structure, optimize the distribution of rare-earth rich (RE-rich) phases in grain boundary, and improve the corrosion resistance and mechanical properties of NdFeB magnets. When the content of Ho increases from 0 to 21.0 wt%, the weight loss of magnets decreases from 2.672 to 0.933 mg/cm², and the microhardness and bending strength increase from 528.74 HV and 374.92 MPa to 633.84 HV and 459.80 MPa, respectively.     

Improvement in magnetic properties,corrosion resistance and microstructure of Nd–Fe–B sintered magnets through intergranular addition of Tb68Ni32

New energy vehicles and offshore wind power industries have a high demand for sintered Nd–Fe–B magnets with high intrinsic coercivity and high corrosion resistance. In this study, the magnetic properties, anticorrosion properties, and microstructure of Nd–Fe–B sintered magnets with the intergranular addition of low-melting-point eutectic Tb₆₈Ni₃₂ alloy powders were investigated. The aim is to determine if the addition of Tb₆₈Ni₃₂ can improve these properties. A low melting-point eutectic alloy Tb₆₈Ni₃₂ powders was prepared as a grain boundary additive and blended with the master alloy powders prior to sintering. The coercivity of the resultant magnets gradually increases from 1468 to 2151 kA/m by adding increasing amounts of Tb₆₈Ni₃₂. At the same time, the remanence first increases and then slightly decreases. After studying the microstructure and elemental composition of the Tb₆₈Ni₃₂ added magnets, it is found that the significant increase in coercivity and the negligible reduction in remanence is due to densification, improved grain orientation, a uniform and continuous boundary phase distribution, as well as the generation of a (Nd,Pr,Tb)₂Fe₁₄B “core–shell” structure surrounding the main-phase grain. Moreover, the corrosion resistance of the magnet is greatly improved owing to the enhancement of electrochemical stability, as well as the optimization of the distribution and morphology of the intergranular phase.     

(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.     

Effect of wheel speed on phase formation and magnetic properties of (Nd0.4La0.6)-Fe-B melt-spun ribbons

The effect of wheel speed on phase formation and magnetic properties of (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 and (Nd_0.4La_0.6)_13.4Fe_79.9B_6.7 ribbons prepared by melt-spinning method was investigated experimentally. Based on X-ray diffraction results, all melt-spun ribbons consist of the main phase with the tetragonal 2:14:1 type structure and the minor α-Fe phase. Magnetic measurements show the maximum magnetic energy product ((BH)_max) and the remanence (M_r) increases firstly and then decreases with the increase of wheel speed, while the coercivity (H_ci) increases, resulting from the variation of the average volume fraction of the α-Fe phase and the average grain size in the melt-spun ribbons. Using Henkel plots, the interaction between the 2:14:1 phase and the α-Fe phase in the melt-spun ribbons was analyzed and the intergranular exchange coupling is manifested. Optimal magnetic properties of H_ci = 7.27 kOe, M_r = 90.94 emu/g and (BH)_max = 12.10 MGOe are achieved in the (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 ribbon with the wheel speed of 26 m/s. It indicates that magnetic properties of Nd-Fe-B melt-spun ribbons with highly abundant rare earth element La can be improved by optimizing alloy composition and preparation process.     

Structure and Magnetic Properties of Nd(Fe,Mo) 12 N x Prepared by Mechanically Alloying

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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.     

Coercivity enhancement of nanocrystalline hot-deformed Nd-Fe-B magnets by low-melting eutectic MM-Cu(MM=La,Ce,Pr,Nd) alloys addition

MM_(85)Cu_(15)(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2,451.1 and 516.5℃.The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase.The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%,and then keeps almost no change with the content further increasing to 5 wt%.The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m,respectively.Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition.Moreover,the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition.Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition.The La,Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries.Therefore,both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.     

Enhancing (de)hydrogenation kinetics properties of the Mg/MgH_2 system by adding ANi_5(A=Ce,Nd,Pr,Sm,and Y) alloys via ball milling

Magnesium(Mg)-based alloys have already been widely studied as the hydrogen storage materials because of their high reversible hydrogen storage capacity,low cost,light weight,etc.However,the poor de/hydrogenation kinetic properties dramatically hinder the practical applications.In this work,the MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites were prepared by a high-energy ball milling method.which can effectively refine the particle size thus improving the kinetic properties.Experimental results reveal that the MgH_2-ANi_5 composites mainly consist of Mg_2 NiH_4,MgH_2 and rare earth(RE) hydride,which will be dehydrogenated to form Mg_2 Ni,Mg and stable RE hydride reversibly.Accordingly,the asmilled MgH_2-ANi_5(A=Ce,Nd,Pr,Sm,and Y) composites with various A-elements can respectively contribute to a reversible hydrogen storage capacity of 6.16 wt%,5.7 wt%,6.21 wt%,6.38 wt%,and 6.5 wt%at a temperature of 300℃,and show much better kinetic properties in comparison to the pure MgH_2 without any additive.In-situ formed Mg_2 Ni and stable RE hydride(such as CeH_(2.73) and YH_2) might act as effective catalysts to significantly improve the hydrogen storage properties of MgH_2.The present work provides a guideline on improving the kinetic properties of the Mg-based hydrogen storage alloys.     

Doping effect of rare-earth (lanthanum,neodymium and gadolinium) ions on structural,optical, dielectric and magnetic properties of copper nanoferrites

Copper and rare earth-doped (RE = La, Gd, Nd) CuFe_1.85RE_0.15O₄ nanoferrites were prepared using the sonochemical method. The effective doping of rare-earth (La³⁺, Nd³⁺, Gd³⁺) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nanoferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet–DRS spectra. The oxidation state of the elements Cu 2p, La 3d, Nd 3d, Gd 3d, Fe 2p and O 1s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.     

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] …     

Superior corrosion resistance and corrosion mechanism of dual-main-phase (Ce15Nd85)30FebalB1M magnets in different solutions

The electrochemical corrosion behavior of both(Ce₁₅Nd₈₅)₃₀Fe_balB₁ M sintered magnets prepared with dual-main-phase method and N45-type magnets was studied in 3.5 wt% NaCl,1.1 wt% NaH₂ PO₄,and2.5 wt% NaOH solutions,respectively.The(Ce₁₅Nd₈₅)₃₀Fe_balB₁ M sintered magnets perform superior corrosion resistance than N45-type magnets in the tested solutions.In general,two ...     

Microstructures and Electrochemical Properties of Cobalt-Free LaNi4.0Al0.2Fe0.4Cu0.4-x Snx (x = 0 ～ 0.4) Electrode Alloys Prepared by Casting

The microstructure, hydriding performance, and electrochemical properties of LaNi4.0Al0.2Fe0.4Cu0.4- x Snx(x = 0 ～ 0.4) hydrogen storage alloys prepared by casting were investigated using XRD, SEM, pressure-composition isotherms, and electrochemical measurements. Substitution of Sn for Cu leads to the precipitation of LaNiSn phase. With increasing amount of tin substitution, cell volume, plateau pressures, and discharge capacities of the alloys decrease,whereas the cycle life of the alloys improves.     

Microstructures and Electrochemical Properties of Cobalt-Free LaNi4.0Ai0.2Fe0.4Cu0.4-x Snx （x = 0 - 0.4） Electrode Alloys Prepared by Casting

The microstructure, hydriding performance, and electrochemical properties of LaNi4.0Ai0.2Fe0.4Cu0.4-x Snx（x = 0- 0.4） hydrogen storage alloys prepared by casting were investigated using XRD, SEM, pressure-composition isotherms, and electrochemical measurements. Substitution of Sn for Cu leads to the precipitation of LaNiSn phase. With increasing amount of tin substitution, cell volume, plateau pressures, and discharge capacities of the alloys decrease, whereas the cycle life of the alloys improves.     

Synthesis, Characterization and Thermal Decomposition of Ln (Me2dtc)3(phen) (Ln=La, Pr, Nd, Sm)

Four solid complexes of Ln(Me2dtc)3(phen) (Ln=La, Pr, Nd, Sm) were synthesized in anhydrous ethanol by the reaction of lanthanide chloride low hydrate with the mixed ligand of sodium dimethyldithiocarbamate and 1, 10-phenanthroline·H2O (phen·H2O), and characterized by elemental analysis, IR spectroscopy, TG-DTG, and X-ray diffraction analysis. TG-DTG with X-ray powder diffraction showed that these compounds could decompose to lanthanide sulfides at relatively lower temperature, which indicated that the title complexes could be favorable precursors to prepare lanthanide sulfides.     

Magnetic properties and microstructure of Fe_(69.5-x)Nd_7B_(21)Nb_(2.5)Ga_x(x=0-1)alloys

The Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)permanent magnets in the form of rods were prepared by annealing the bulk amorphous alloys.The magnetic properties,phase evolution and microstructure of the alloys were investigated systematically.It is found that the glass forming ability(GFA), microstructure and magnetic properties are sensitive to Ga content for Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)bulk alloys.The annealed alloys are mainly composed of soft α-Fe,hard Nd_2 Fe_(14)B and nonmagnetic Nd_(1.1)Fe_4 B_4 phases.When x = 0.3,the optimally annealed magnets exhibit magnetic properties of the remanence Br = 0.63 T,intrinsic coercivity H_(cj) = 368.68 kA/m and maximum energy product(BH)_(max) = 33.73 kJ/m~3.Furthermore,magnetic field heat treatment at the temperature close to Curie temperature of Nd_2 Fe_(14)B phase was applied to the annealed Fe_(69.2)Nd_7 B_(21)Nb_(2.5)Ga_(0.3) magnet.The results of X-ray diffraction(XRD)and transmission electron microscopy(TEM)indicate that the magnetic field heat treatment can be beneficial for the precipitation of α-Fe.Thus,the B_r,H_(cj) and(BH)_(max) are enhanced by 8.7%,6.3% and 16.3%,respectively.     

Preparation and Structure of Mg2-xRExNi （RE = La, Ce, Pr, Nd, Y） Ternary Alloys

A series of Mg2-xNdxNi (x =0.05, 0.1, 0.2, 0.3) alloys and Mg1.95RE0.05Ni (RE= La, Ce, Pr, Nd, Y)ternary alloys were prepared by ball milling of mixted powder of Mg, Ni, RE and sintering under the protection of argon. XRD analysis shows that Mg2-xNdxNi (x = 0.05, 0.1 ) and Mg1.95RE0.05Ni consist of single phase with the same crystal structure as Mg2Ni. While three-phase alloys including Mg2Ni, NdNi and NdMgNi4 were formed in Mg1.8Nd0.2Ni and Mg1.7Nd0.3Ni alloys respectively. The lattice constants of Mg2Ni in those ternary alloys were calculated. The decomposition of Mg2Ni occurs in the milling process of Mg2Ni and Mg1.95RE0.05Ni alloys respectively. For the latter, another earlier reaction occurs in milling process, which means that atoms of RE are separated from crystal structure of Mg2Ni and form relevant oxides by combination with oxygen existed in argon atmosphere.