Xuexu Gao

Magnetostriction and microstructure of the melt-spun Fe83Ga17 alloy

The ribbons with different thicknesses of Fe83Ga17 alloy were prepared by melt spun. The maximum magnetostriction of −2100ppm has been obtained in the ribbon with the thickness of 75μm. The microstructures of the ribbons were determined by x-ray diffraction. It was found that DO3 structure emerges in those ribbons melt spun at a higher cooling rate. This special DO3 structure is favorable to the enhancement of magnetostriction. It is considered that more short-range ordering of Ga atoms appeared when liquid alloy was solidified with a certain extreme cooling rate. Such short-range ordering of Ga atoms brings a local stress and results in the giant magnetostriction. The large demagnetizing magnetic energy in the normal direction of the ribbons causes the magnetic moments parallel to the ribbon plane. When an applied magnetic field is perpendicular to the ribbon plane, the magnetic moments turn 90° and generate giant magnetostriction.

Influence of zirconium addition on microstructure, magnetic properties and thermal stability of nanocrystalline Nd12.3Fe81.7B6.0 alloy

Abstract Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7–xZrxB6.0 (x=0–3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnetometer (VSM) revealed that Zr addition was significantly effective in improving the magnetic properties at room temperature. The intrinsic coercivity Hci of the optimally processed ribbons increased monotonically with increasing Zr content, from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. Unlike the coercivity, the remanence polarization Jr increased first with Zr addition, from 0.898 T up to 1.041 T at x=1.5, and then decreased with further Zr addition. The maximum energy product (BH)max behaved similarly, increasing from 103.1 kJ/m3 to a maximum of 175.2 kJ/m3 at x=1.5. Microstructure studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM) had shown a significant microstructure refinement with Zr addition. The absolute values of temperature coefficients of induction and coercivity were significantly increased with increasing Zr content, indicating that Zr was detrimental to thermal stability of the melt-spun Nd2Fe14B-type material.

Diffusion of Nd-rich phase in the spark plasma sintered and hot deformed nanocrystalline NdFeB magnets

The role of the Nd-rich phase in developing microstructure and properties of isotropic and anisotropic NdFeB magnets has been investigated. Melt spun Nd-rich Nd13.5Fe73.5Co6.7Ga0.5B5.6 and Fe-rich Nd7.7Pr2.6Fe84.1B5.5 alloy powders were mechanically mixed with different ratios. The mixed powders were consolidated into isotropic magnets and anisotropic magnets by spark plasma sintering (SPS) and SPS followed by hot deformation, respectively. The composition and microstructure of diffusion area between Nd-rich and Fe-rich compositions for isotropic and anisotropic magnets were investigated. The gradient distribution of Nd content from Nd-rich to Fe-rich area due to the diffusion of liquid Nd-rich phase in the SPS and hot deformation was observed, which leads to gradually changes in grain structure. The remanent polarization of 1.29 T, coercivity of 995 kA/m, and maximum energy product of 293 kJ/m3 are obtained for an anisotropic magnet. The role of the Nd-rich phase has to be carefully considered in order to achieve deformation anisotropy and fine grains in the NdFeB magnets.The role of the Nd-rich phase in developing microstructure and properties of isotropic and anisotropic NdFeB magnets has been investigated. Melt spun Nd-rich Nd13.5Fe73.5Co6.7Ga0.5B5.6 and Fe-rich Nd7.7Pr2.6Fe84.1B5.5 alloy powders were mechanically mixed with different ratios. The mixed powders were consolidated into isotropic magnets and anisotropic magnets by spark plasma sintering (SPS) and SPS followed by hot deformation, respectively. The composition and microstructure of diffusion area between Nd-rich and Fe-rich compositions for isotropic and anisotropic magnets were investigated. The gradient distribution of Nd content from Nd-rich to Fe-rich area due to the diffusion of liquid Nd-rich phase in the SPS and hot deformation was observed, which leads to gradually changes in grain structure. The remanent polarization of 1.29 T, coercivity of 995 kA/m, and maximum energy product of 293 kJ/m3 are obtained for an anisotropic magnet. The role of the Nd-rich phase has to be carefully considered in order ...

Crystal structure and magnetic properties of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling

Abstract SmCo 6.6 Nb 0.4 nanoflakes with TbCu 7 structure were successfully prepared by surfactant-assisted high energy ball milling (SA-HEBM) with heptane and oleic acid as milling medium. The microstructure, crystal structure and magnetic properties were studied by scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. The effects of ball milling time on the c -axis crystallographic alignment and coercivity of the nanoflakes were systematically investigated. The research showed that the nanoflakes had an average thickness of 100 nm, an average diameter of 1 μm, with an aspect ratio as high as 100. As the ball milling time increased from 2 to 8 h, the reflection peaks intensity ratio I (002) / I (101) , which indicated the degree of c -axis crystal texture of the SmCo 6.6 Nb 0.4 phase, increased first, reached a peak at 4 h, and then decreased. Meanwhile, the coercivity of the nanoflakes also increased first, reached a peak at 13.86 kOe for 4 h, and then decreased.

Orientation textures of grains and boundary planes in a hot deformed SmCo5 permanent magnet

The electron backscattered diffraction technique was used to identify the orientation textures of both grains and boundary planes in a hot deformed SmCo5 permanent magnet. The results show that the orientations of SmCo5 grains are strongly textured and the {0001} orientations are remarkably preferred. Moreover, grain boundary planes are also textured. Three symmetry equivalents of Σ13a boundaries, namely the 27.796°/[0001] boundary, the 32.204°/[0001] boundary and the 92.204°/[0001] boundary, are favored, and the occurring frequency of Σ13a boundaries is 5 times higher than that of the random boundaries. Potential effects of the orientation textures of grains and boundary planes on the magnets are also proposed.

Effect of zirconium content on exchange coupling and magnetization reversal of nanocrystalline Nd12.3Fe81.7–xZrxB6 alloy

Abstract The effect of Zr content on exchange coupling and magnetization reversal of the Nd 12.3 Fe 81.7– x Zr x B 6 ( x =0–3.0) ribbons was systematically investigated. Interaction domains were imaged by magnetic force microscopy (MFM). The strength of interactions determined by Wohlfarths analysis increased first with Zr content x increasing, reached the maximum value at x =1.5, and then decreased with x further increasing. Initial magnetization curves and dependence of coercivity and remanence on applied magnetic field showed that the mechanism of coercivity in all samples was mainly of exchange coupling pinning type, which was enhanced with x increasing. It was found by three-dimensional atom probe (3DAP) that Zr atoms did not partition into the Nd 2 Fe 14 B hard magnetic phase, but significantly enriched at the interfacial region.

Microstructure evolution and magnetic properties of overquenched Pr8Fe86B6 ribbons during annealing

Microstructure evolution and magnetic properties of overquenched Pr8Fe86B6 ribbons during annealing have been investigated. The results showed that, in as-quenched state, the microstructure of the ribbons consists of a mixture of amorphous phase (Am)+Pr2Fe14B+a-Fe, Am+a-Fe and only amorphous phase, respectively, for the wheel speed of 22, 26, and 30 m/s. Depending on the overquenched precursor, the microstructure evolution of the ribbons during annealing can be classified into: (1) Am+Pr2Fe14B+a-Fe→Pr2Fe14B+a-Fe; (2) Am+α-Fe→Am′+a-Fe→a-Fe+Pr2Fe23B3+Pr2Fe14B→Pr2Fe14B+a-Fe; and (3) Am→Am+a-Fe→Pr2Fe23B3+a-Fe→Pr2Fe14B+a-Fe. In all cases, the microstructure of optimally annealed ribbon samples consist of magnetically hard Pr2Fe14B and soft magnetic a-Fe phases. The magnetic properties achieved by optimal annealing were found to be strongly dependent upon the initial quenching rate of the unannealed precursor. A fairly significant drop in both Hci and Br was observed with the increase of quenching rate of the p...

Effect of yttrium on the mechanical and magnetostrictive properties of Fe83Ga17 alloy

Polycrystalline rod samples of (Fe83Ga17)100–xYx (x=0, 0.16, 0.32, 0.48, 0.64) were prepared by induction melting under argon atmosphere. Effect of yttrium on the mechanical and magnetostrictive properties of Fe83Ga17 alloy was investigated. Small amount of yttrium (0.16 at.%) increased the tensile strength of as-cast Fe83Ga17 alloys to 674 MPa and improved the ductility with elongation of 4.2% at room temperature. The Y2Fe17–xGax (6≤x≤7) phase was formed in the Y-doped Fe83Ga17 alloy since yttrium was hardly dissolved into the α-Fe lattice. Y2(FeGa)17 secondary phase dispersed along the grain boundaries and inside the grains played an important role for the enhancement of mechanical property. The 0.64 at.% Y-doped alloy had magnetostriction of 133 ppm, which was thought to be associated with the alteration of the grain shape and preferential orientation along the axial direction of rods.

Magnetic Properties and Phase Transformation of Tb1-x PrxFe1.96 (x = 0 to 0.7) Compounds

The magnetic properties and the phase Transformation of Tb1-xPrxFe1.96(x = 0 to 0.7) compounds were studied by means of vibrating sample magnetometer(VSM), X-ray diffraction(XRD) and SEM back-scattered electron (BSE). The result indicates that the saturation magnetization σs of compounds along an easy axis decreases with the addition of Pr contents, which reduces from 77.24 Am2 · kg−1 (x = 0) to 11.84 Am2·kg−1(x = 0.5) and then returns to 37.14 Am2·kg−1 (x = 0.7). The non-cubic phases appear when x exceeds 0.2, and the matrix of Tb1-xPrxFe1.96 compounds changes from (Tb, Pr)Fe2 phase with x = 0 to (Tb, Pr)Fe3 phase with x = 0.4, and at last to (Tb, Pr)2Fe17 phase in Tb0.3Pr0.7Fe1.96. Moreover, the structure of the compounds may become more complex with the increase of Pr content.

Variable stiffness Fe82Ga13.5Al4.5 spring based on magnetoelastic effect

The elastic modulus of magnetostriction materials can be controlled in real time by changing the magnetic field. Accordingly, spring with variable stiffness coefficients is available. In this work, Fe82Ga13.5Al4.5 wires of 3.5 mm diameter were prepared by heat forging, rolling, and drawing. Holding at 600 °C for 30 min after annealing at 1100 °C significantly improved the magnetostriction and soft magnetic properties of drawn wires. The tensile test shows two types of relative strain at the initial stage of tension: the elastic modulus under the condition of unsaturated magnetized (Ea) and purely mechanical elastic modulus (Es). The modulus defect ((Es−Ea)/Es × 100%) due to the additional magnetoelastic strain is up to 41.6%. Then, Fe82Ga13.5Al4.5 spring and the loading way of the magnetic field were designed and processed. By tuning the magnetic field strength, the stiffness coefficient of the spring is controlled accordingly. An apparent change in the stiffness coefficient of 10.86% is observed by furth...