Influence of rare earth element terbium doping on microstructure and magnetostrictive properties of Fe81Al19 alloy

Fe81Al19Tbx (x =0,0.05,0.1,0.2,0.3,0.4) alloys were prepared by a non-consumable vacuum arc melting technique under an inert argon gas atmosphere.The microstruc...     

Enhanced magnetic properties of Ce17Fe76.5Co1Zr0.5B6 alloys by magnetic field heat treatment

In the present work, Ce₁₇Fe_76.5Co₁Zr_0.5B₆ ribbons were prepared by a direct melt spinning method. The effects of chamber pressure and magnetic field annealing temperature on the magnetic properties and microstructures of the alloys were investigated. The grain size and content of Ce₂Fe₁₄B phase can be changed by adjusting the chamber pressure, and the optimal magnetic performance is obtained at 0.04 MPa. The magnetic properties can be influenced under magnetic field heat treatment. When the annealing temperature is lower than the Curie temperature, the refinement and a uniform distribution of the grains is obtained. The irreversible magnetic susceptibility curve reveals that magnetic field heat treatment enhances the exchange coupling interaction between grains of the Ce₂Fe₁₄B phase. When the magnetic field annealing temperature is 438 K, the alloy displays the optimal magnetic properties. Compared with the as-spun sample, the values of intrinsic coercivity (H_ci), remanence (B_r) and maximum energy product ((BH)_max) increase by 3.4%, 9.8% and 18.7%, respectively. This work provides an effective approach by which to enhance the magnetic properties of Ce–Fe–B alloys.     

Effect of copper on magnetostriction and mechanical properties of TbDyFe alloys

The intrinsic brittleness of the TbDyFe alloy significantly decreases its mach inability and applications.This paper aims to improve the toughness of TbDyFe alloy by adding Cu. Various alloys of the type(Tb_(0.3)Dy_(0.7))_(0.37)Fe_(0.63-χ)Cu_χ(χ=0, 0,01.0.03, 0.05, 0.08, 0.1) were fabricated by an arc melting furnace under a high purity argon atmosphere. The microstructure, magnetostrictive properties and mechanical performance were studied systematically. The results show that the (Tb,Dy)Cu phase forms in these alloys upon the addition of Cu. Correspondingly, their toughness improves, attributed to the formation of a (Tb,Dy)Cu phase. Compared to the Cu-free alloy, the fracture toughness (Kic) increases 2-3 times with increasing Cu content. However, the magnetostriction performance of these alloys declines with Cu addition, due to the low-magnetic performance of the (Tb,Dy)Cu phase at room temperature. Compared with other alloys, the alloy with the addition of 1at%Cu shows the best compromise between the saturation magnetostriction and fracture toughness.     

Effects of manganese substitution on magnetic and magnetostrictive properties of Tb0.5Dy0.5(Fe1-xMnx)1.92/epoxy composites with spherical single-crystal particles

Spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92(x=0,0.05,0.10 and 0.15) single-crystal particles were prepared.The magnetic anisotropy of the alloy decreases as x increases from 0 to 0.15.Subsequently,we prepared giant magnetostrictive composites with these spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92 single-crystal particles.As a consequence,well <111>-orie nted Tb_0.5Dy_0.5(Fe_1...     

Enhanced maximum energy product of(Sm_(1-y)Y_y)_2Fe_(17)N_x caused by abundant yttrium doping

Replacement of samarium(Sm) with abundant yttrium(Y) can help solve the potential shortage of Sm in the preparation of promising Sm_2 Fe_(1)7 N_x magnets.In this article,phase composition,microstructure and magnetic properties of(Sm_(1-y)Yy)_2 Fe_(17)N_x(y=0,0.2,0.4,0.6,0.8,1.0) were investigated.Maximum energy product(BH)_(max) is improved when less than 40 at% Y is doped in(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder.In particular,when 20 at% Y replaces Sm,(BH)_(max) of(Sm_(1-y)Y_y)_2 Fe_(17)N_x powder increases by 15.1% from 131.7 to151.6 kJ/m~3.The effect of annealing temperature on the structural properties of high Y doping(Sm_(0.6)Y_(0.4))_2 Fe_(17) and the magnetic properties of the corresponding nitrides were subsequently investigated.In the RE_2 Fe_(17) phase grain combination process,the interlaced structure of the rhombohedral Th_2 Zn_(17)-type structural phase and the hexagonal Th_2 Ni_(17)-type structural phase is formed.Due to shortrange exchange coupling,the nitride with the highest content of two interlaced RE_2 Fe_(1)7 phases has the highest magnetic properties:B_r=1.23 T,H_(cJ)=443.9 kA/m and(BH)_(max)=197.6 kJ/m~3.     

Corrosion mechanism of H_2O on Sm_2Fe_(17) and nitrogenation process of corroded Sm_2Fe_(17)

Sm_2 Fe_(17) prepared by reduction-diffusion method needs to be washed with water to remove calcium oxide. Electrochemical corrosion occurs when Sm_2 Fe_(17) powder is in contact with liquid water. Corrosion mechanism of H_2 O on Sm_2 Fe_(17) powder and nitrogenation process of corroded Sm_2 Fe_(17) were studied by analyzing the structure and morphology. It is indicated that the metallic hydroxide forms and deposits on the Sm_2 Fe_(17) powder surfaces during water corrosion. At the same time, oxygen and hydrogen enter the unit cell of Sm2 Fe_(17), causing a slight increase in Curie temperature. In the subsequent nitriding process,the hydroxide is dehydrated and hydrogen is desorbed. The resulting oxide reacts with Sm_2 Fe_(17)N_x to form a-Fe and Sm_2 O_3. Thermodynamic calculations using the HSC Chemistry 6.0 software indicate that the reaction can occur spontaneously. The effect of water corrosion on the magnetic properties of the nitride can be eliminated by hydrogen reduction prior to nitriding.     

Preparation and magnetic properties of anisotropic Nd_2Fe_(14)B/Sm_2Co_(17) hybrid-bonded magnets

In the present work, anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets were prepared with different Nd-Fe-B contents. It is found that the particle distributions and ratios between the two magnetic phases have important roles in the magnetic properties, microstructures and thermal stability of the magnets. With increase of Nd-Fe-B content, the saturation magnetization of the anisotropic hybrid magnet increases significantly, however, coercivity decreases, and the demagnetization curves show magnetically single-phase behavior. The anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets exhibit a maximum energy product and remanence of 14.15 MGOe and 99.53 A·m~2/kg, respectively, when the NdFe-B content is 70 wt% at room temperature. Furthermore, the hybrid magnets also have better thermal stability at elevated temperatures due to the interaction between the two magnetic particles.     

铸造法制备Al63Cu25Fe12准晶

通过常规铸造法制备了Al63Cu25Fe12准晶合金,并对其热处理工艺进行了初步探索,采用显微镜和扫描电镜观察了金相组织,采用XRD衍射分析了其中的准晶相及类似晶体相。研究结果表明,铸造法制备的AlCuFe准晶材料中主要由二十面体I相、立方结构β相和单斜结构入相3种物相组成。常熔铸制备的Al63Cu25Fe12准晶合金在接近I相熔点长时间退火,可以显著提高I相的含量。     

Effect of carbon coating on electrochemical properties of AB3.5-type La-Y-Ni-based hydrogen storage alloys

The superlattice La-Y-Ni-based hydrogen storage alloys have high discharge capacity and are easy to prepare.However,there is still a gap in commercial applications because of the severe corrosion of the alloys in electrolyte and poor high-rate dischargeability(HRD).Therefore,(LaSmY)(NiMnAl)_3.5 alloy was prepared by magnetic levitation induction melting,and then the alloy was coated with different contents(0.1 wt%-1.0 wt%) of nano-carbons by low-temperature sintering with sucrose as th...     

Phase forming law and electrochemical properties of A2B7-type La-Y-Ni-based hydrogen storage alloys with different La/Y ratios

The effects of different proportions of La and Y elements in the A-side on the structure and properties of A₂B₇-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)₂Ni₇ hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y₂Ni₄ precursor and different AB₅-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K.All the alloys only contain Ce₂Ni     

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.     

Study on the Easy Direction of Magnetization of Sm_（0．88）Dy_（0．12）Fe_2 Alloy

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新型三元合金Nd(Y)-Fe-B吸波材料的制备及其性能研究

通过真空熔炼、行星球磨和适当退火处理后制得一种新型吸波材料NdxYFe92.56-xB6.5(x=4,5,6,7).对其性能进行测试后表明,退火前后各样品对微波的吸收量在所测频率范围内整体较高波动较小,其中,未退火处理的样品在频率为12.41GHz处最大吸收量达38.084dB,在下退火15min后样品吸波性有显著提高,在频率为12.04GHz处最大吸收量达94.573dB.     

微量硼和铌对铸造Ni_(50)Al_(20)Fe_(30)合金组织及性能的影响

研究了微量硼和 2 % Nb对铸造 Ni5 0 Al2 0 Fe30 合金组织及性能的影响。结果表明 :微量硼的加入可以改善 Ni5 0 Al2 0 Fe30 合金的强度与塑性 ,最佳硼含量为 0 .0 2 %～ 0 .0 5 % ;此外 ,微量硼的加入影响该合金的共晶区 ,从而明显改变合金的微观组织形态。在硼含量为 0 .0 2 %时 ,该合金主要处于 β相 (Ni Al)与 γ相的共晶区 ,这对合金的室温塑性极为有利。添加 2 % Nb可明显提高该合金的压缩屈服强度并改善塑性。在室温、6 5 0℃和 10 0 0℃ ,该合金的压缩屈服强度分别提高 30 %、5 9%和 36 %     

Phase constitutions,growth pattern and mechanical properties of Mg-1.4Gd-1.2Y-xZn-0.15Zr(at%) alloys

The effects of minor Zn(0.2 at%,0.4 at%,0.6 at%) on the microstructures and mechanical properties of Mg-1.4 Gd-1.2 Y-0.15 Zr(at%) alloys were systematically explored.Results reveal that increasing Zn content leads to the increase of the intergranular phases and the change of their composition from Mg_24(Gd,Y)_5 phase and(Mg,Zn)_3(Gd,Y) phase to 18 R-LPSO phase and(Mg,Zn)_3(Gd,Y) phase.Mg_24(Gd,Y)_5 phase is body-centered cubic structure and shares the same lattice constant with Mg_24Y_5 while(Mg,Zn)_3(Gd,Y)phase is face-centered cubic structure with lattice constant of 0.72 nm,slightly lower than Mg_3Gd.18RLPSO structure is identified to be monoclinic with c-axis not strictly vertical to the bottom surface but93.5°.The growth patterns of intergranular phases change from the divorced growth to coupled growth as compositions change.Moreover,the mechanical performance improves with Zn rising,ascribed to the decrease of brittle phases at grain boundaries and the increase of LPSO structure phases.     

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.     

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4(Ti-6 Al-4 V)and 4 J29 Kovar alloy(Fe-29 Ni-17 Co)were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that(Fe,Co,Ni)-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_(17) Mn_3 and Al_6 Ti_(19) were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.     

Effects of RE (La,Ce) on fcc-bcc martensitic transformation of iron via Bain transformation path

The fundamental understanding of the effects of rare earth (RE) on the phase transformation of Fe-based alloys is essential in the development of advanced RE-containing high strength steels. In this work, we investigated the effects of La and Ce on the martensitic phase transformation of Fe in terms of the driving force and minimum energy path (MEP) using the first-principles calculations. The calculations of formation energy show that the RE substitution increases the stabilization of fcc-Fe and decreases that of bcc-Fe, thus decreasing the driving force of phase transformation. Meanwhile, the analysis based on the generalized solid-state nudged elastic band (G-SSNEB) method indicates that in the RE-containing systems, an additional energy barrier appears when the phase transformation proceeds along the Bain transition path to c/a ratio of 1.14 in the FM state, which is associated with a sudden decrease in magnetization due to the hybridization between the orbits of the RE atoms and those of the nearest neighbor Fe atoms. The results of potential-energy surfaces (PES) confirm that magnetic ordering and lattice volume change simultaneously with the Bain transition, and in comparison to pure Fe, the variation between the onset and the end structural volumes of the phase transformation is slight for the RE-containing Fe systems.     

Enhanced magnetic properties of anisotropic Nd-Fe-B nanocomposites by Fe(C)coating

Nanostructured anisotropic Nd-Fe-B/Fe(C) composite powders were prepared by coating Fe(C) softmagnetic nanoparticles on HDDR Nd-Fe-B hard magnetic powders using iron pentacarbonyl Fe(CO)_5 as soft-phase precursor.The effect of Fe(CO)_5-loading amount on soft-phase purity,coating morphology and magnetic properties of the composite powders was investigated.Dense and continuous Fe(C) softphase coatings with average particle sizes of 58-68 nm are obtained at Fe(CO)_5 loading amounts of x 12 wt%,leading to enhanced remanence and improved energy product of the coated powders.Positive value in δM-plots and single-phase-like demagnetization curves are observed in the Nd-Fe-B/Fe(C) composite powders,indicating the exchange coupling effect between the coated Fe(C) soft phases and the Nd-Fe-B hard phase.     

粉末冶金NiFe_(19)Al_(25)合金的组织与性能研究

用粉末冶金技术制备Ni-Fe-Al合金,将Ni、Fe、Al的元素粉与预合金粉等量混合后在500MPa下压制成形,于1280℃的温度烧结后进行热处理,对合金烧结态和淬火态进行密度、力学性能检测及X射线衍射分析、断口形貌及微观组织观察。结果表明:NiFe19Al25合金烧结态为(β+γ)双相组织,合金的密度达6.54g/cm3(相对密度为94.0%),抗拉强度达到771MPa,形变量为5.3%;合金淬火态处于(β′+γ)双相区,具有马氏体结构的NiFe19Al25合金在应力作用下呈现出线性超弹性,抗拉强度达到761MPa,形变量高达8.1%,最高形变恢复量超过4%。