Xiaoqian Bao

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.

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.

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.

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...

Electromagnetic induced voltage signal to magnetic variation through torquing textured Fe81Ga19 alloy

The results of a study on the suitability of Fe-Ga alloys for torque sensor applications are presented. A Fe81Ga19 rod with a ⟨100⟩ preferred orientation along the length direction is prepared for the torque shaft and as the electromagnetic induction sensitive element, which is wound with three coils for signal excitation, signal pickup, and applied bias magnetic field, respectively. An apparent decrease in the induced voltage signal (peak voltage) of 3.88 mV is observed as the torque loading is 50 N m in the presence of a sine excitation signal (10 V, 1 kHz) and a bias current of 0.5 A. Meanwhile, a good repeatability and stress sensitivity are obtained, especially in the low torque range. These behaviors stem from the stress induced decrease in the magnetic permeability and the rotation of the arranged magnetic moment. Here, we use the Fe81Ga19 alloy as the shaft material; nevertheless, in practical use, the same effect can be achieved by forming a Fe-Ga layer with large magnetostriction on the surface ...

Tailoring magnetostriction with various directions for directional solidification Fe82Ga15Al3 alloy by magnetic field heat treatment

The magnetostriction of the Fe82Ga15Al3 alloy, along the length and width, can be tailored by applying a magnetic field heat treatment. In this work, the Fe82Ga15Al3 sheet was cut from the directional solidified Fe82Ga15Al3 alloy with the ⟨100⟩ preferred orientation and was annealed at 720 °C for 30 min under a magnetic field of 800 Oe along the length direction with a heating and cooling rate of 100 °C/min. The magnetostrictive properties along the length and width directions were modified to λ// = 7 ppm and λ⊥ = −210 ppm from λ// = 210 ppm and λ⊥ = −10 ppm for the initial sample prior to the magnetic field heat treatment. The cellular-like magnetic domain structure was composed of parallel 180° stripe domains and vertical 90° domains observed using a magnetic-force microscope. The change in magnetostriction along parallel and perpendicular directions was mainly resulted from the rotation of the magnetic domain units.

Effect of annealing time on the exchange coupling interactions and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons

The influence of annealing time on the magnetic properties and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons was systematically investigated by the methods of vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Interaction domains derived from strong exchange coupling interactions between hard and soft magnetic grains were imaged using magnetic force microscopy (MFM). Maximum remanence, intrinsic coercivity, and maximum energy product values were obtained in the ribbons annealed at 700°C for 15 min, which were composed of Pr2(Fe, Co)14B, α-(Fe, Co), and slight Pr2(Fe, Co)17 phases. Although Jr Hd, and (BH)max decreased gradually with further increase of annealing time, it is emphasized that comparatively high Jr and Hci and (BH)max were obtained in a wide annealing time period of 15 to 360 min. The shape of initial magnetization curves and hysteresis loops change as a function of annealing time, indicating different magnetization reversal routes, which can be fully explained by the corresponding microstructure.

Magnetic Domain Motion and Magnetostriction in the Fe–Ga Sheets

The magnetic domain motion with varying magnetic field is investigated by magneto-optic Kerr microscopy on a slightly Goss misoriented Fe-Ga rolled sheet, and a close relationship between the magnetostriction and the domain motion is reported during the magnetization process. Along the rolling direction (RD), a high magnetostriction value λ// of 281 ppm is observed under no prestress for the sheet. The magnetic domains on the ~12° misoriented Fe-Ga (110) surface appear in the lancet shape and align as lancet comb structures. The lancet domain motion on the surface well explains the magnetostrictive performance λ// with the consideration of 90° domains within the lancet structure. The rapid increase of magnetostriction is attributed to the quick motion of 90° domains within the lancet structure under the field below 70~100 Oe. Under the higher magnetic field, these lancet domains gradually disappear with the field increasing, accompanied with the approach to the saturation magnetostriction along the RD.

Microstructure and magnetostrictive performance of NbC-doped oriented Fe-Ga alloys

The <100> oriented Fe83Ga17 alloy rods with various NbC contents less than 1at% were prepared by the directional solidification method at a growth rate of 720 mmh−1. Low NbC-content was found to affect the oriented grain growth and slightly improve the <100> orientation. Flat grain boundaries in the alloys with low NbC contents less than 0.2at% became greatly curved at higher NbC contents, and a large amount of Nb-rich precipitates were observed in the alloys with high NbC contents. Small amounts of NbC, less than 0.2at%, resulted in an increase in magnetostrictive strain due to the improvement of the <100> orientation, and a high magnetostrictive strain value of 335 10−6 under a pre-stress of 15 MPa was obtained in the 0.1at% NbC-doped alloys. The magnetostrictive performance obviously decreased with the NbC addition higher than 0.5at%, and the strain sensitivity under no pre-stress was lower than that in the binary Fe-Ga alloy.

Effect of cobalt substitution on magnetic properties and microstructure of nanocrystalline (NdDyTb)12.3(FeZrNbCu)81.7B6.0 ribbons

Abstract Effect of Co substitution and annealing treatment on the formation, magnetic properties and microstructure of (NdDyTb) 12.3 (FeZrNbCu) 81.7- x Co x B 6 ( x =0–15) ribbons prepared by rapid quenching and subsequent annealing was systematically investigated by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM) and vibrating sample magnetometer (VSM). Phase analysis revealed single-phase material. The remanence polarization J r and maximum energy product ( BH ) max increased with increasing x from 0 to 12 and then decreased for x =15. The intrinsic coercivity H ci of (NdDyTb) 12.3 (FeZrNbCu) 81.7– x Co x B 6 ribbons optimally processed decreased from 1308.7 kA/m for x =0 to 817.4 kA/m for x =15. Optimum magnetic properties with J r =1.041 T, H ci =944.9 kA/m and ( BH ) max =155.1 kJ/m 3 were achieved by annealing melt-spun ribbon ( x =12) at 675 °C for 10 min. There was no significant influence of Co substitution on microstructure.