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Fe83Ga17 (at. %) coatings with a thickness of 270-500 μm were prepared on 316L stainless steel by high velocity oxy-fuel spraying technology. The coatings exhibited a lamellar structure, and the magnetostriction reached 34.5 ppm. The magnetostrictive coatings were applied to electromagnetic acoustic transducers (EMATs), where the different bias magnetic fields and coating thicknesses were considered to examine the ultrasonic guided wave sensing capability and the detection sensitivity. The 180-kHz ultrasonic guided waves were captured from artificial defects and the pipe end under different bias magnetic fields. Among them, the EMATs exhibited the best sensing performance under a bias magnetic field of 255.7 Oe. Meanwhile, magnetostrictive stress induced the decrease of the magnetic permeability and the rearranged magnetic moment, resulting in a large strain sensitivity (dλ/dH). Because of the relatively good field sensitivities in magnetization and magnetostriction, the EMATs using Fe83Ga17 coating with a thickness of 500 μm exhibited better detection sensitivity than that of 300 μm. This work provides a good prospect of Fe-Ga alloy coatings applied in non-destructive testing. [ABSTRACT FROM AUTHOR]

The ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheets with the thickness of 0.06–0.15 mm were prepared from the secondary recrystallized sheets via rolling. The recrystallization texture evolution, magnetostriction and mechanical properties in the rolled sheets during the annealing at 1200 °C for 1.5–3 h were investigated. Results indicated that the magnetostriction of the ultra-thin sheet was closely related to the texture evolution depended on heat-treatment process. The major textures in the as-rolled sheet were {113}<361> and {111}<112> deformed texture, and the saturation magnetostriction was only ~ 63 ppm. However, an ideal {100}<001> texture was obtained in the recrystallized sheets annealed at 1200 °C for 2 h, producing a corresponding magnetostriction of 147 ppm. Based on texture analysis, the appearance of cubic texture is mainly the consequence of the existence of cubic nuclei and transitional orientation {113}<361> in deformed grains as well as the lowest surface energy at the (100) plane. Compared with Goss secondary recrystallized (Fe83Ga17)99.9(NbC)0.1 sheet with a thickness of 0.3 mm, the tensile ductility of cubic recrystallized ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheet was obviously improved from 2.4 to 4.4%, which was mainly attributed to the primary recrystallized microstructure with small grain size and transgranular fracture mode. The ultra-thin cubic textured (Fe83Ga17)99.9(NbC)0.1 sheets could significantly reduce eddy current losses at high frequency, and meet the requirements of low eddy current loss and high toughness for specific applications, such as ultrasonic applications and torque sensors. [ABSTRACT FROM AUTHOR]

Magnetostrictive (Co70 Fe30)99.8 (NbC)0.2 sheets in 0.3 mm thickness were prepared successfully by forging, hot rolling, and cold rolling. In this paper, the effect of heat treatment on texture evolution and magnetostriction of the (Co70 Fe30)99.8 (NbC)0.2 sheets was investigated. The strong <110> fiber texture along the rolling direction, which originated from the cold-rolling process was retained in the annealed (Co70 Fe30)99.8 (NbC)0.2 sheets with the annealing temperature ranging from 500 °C to 700 °C. When the annealing temperature increased to 800 °C, the proportion of <100>fiber texture markedly increased, and the magnetostriction increased from 93 to 135 ppm. As the annealing temperature reached higher than 900 °C, a proportion of <100> fiber texture gradually reduced due to the secondary recrystallization. As a result, the magnetostriction of (Co70 Fe30)99.8 (NbC)0.2 sheets decreased. [ABSTRACT FROM AUTHOR]

The properties of Fe–Ga thin films on PZT substrate were investigated in this paper. In the Fe–Ga/PZT (ME) devices the Fe–Ga magnetostrictive films act as a driver, therefore it should exhibit a good magnetic and mechanical properties. During sputtering, Ar pressure was changed and Fe–Ga thin films were obtained. It is shown that there is a strong relationship between the gas pressure and film adherence, conductivity, magnetic, and mechanical properties of Fe–Ga thin films. We found that the Fe–Ga/PZT devices with high Young’s modulus and high permittivity also performance good in the ME coupling test. The ME coefficient was 0.17 V/cm Oe at resonance frequency, although the thickness of Fe–Ga film only was about 300 nm. [ABSTRACT FROM AUTHOR]

Oriented polycrystalline CoFe 2 O 4 have been prepared via a ceramic method. The CoFe 2 O 4 powder was mixed with polyvinyl alcohol solution to produce semisolid slurries. The slurries were oriented under a magnetic field of 2 T, and were then sintered at 1623 K. The maximum magnetostriction λ s up to −270×10 −6 and strain derivative ( dλ / dH ) max of 7.7×10 −9 m/A were achieved for oriented samples. Results show that a preferred <001> orientation has been obtained within oriented sample. [ABSTRACT FROM AUTHOR]

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 \lambda \mathrm { {//}} of 281 ppm is observed under no prestress for the sheet. The magnetic domains on the \sim 12^\circ 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 \lambda \mathrm { {//}} 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 $70\sim 100$ 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. [ABSTRACT FROM AUTHOR]

As giant magnetostrictive materials with low magnetocrystalline anisotropy, Tb-Dy-Fe alloys are widely used in transducers, actuators and sensors due to the effective conversion between magnetic energy and mechanical energy (or acoustic energy). However, the intrinsic brittleness of intermetallic compounds leads to their poor machinability and makes them prone to fracture, which limits their practical applications. Recently, the addition of a fourth element to Tb-Dy-Fe alloys, such as Ho, Pr, Co, Nb, Cu and Ti, has been studied to improve their magnetostrictive and mechanical properties. This review starts with a brief introduction to the characteristics of Tb-Dy-Fe alloys and then focuses on the research progress in recent years. First, studies on the crystal growth mechanism in directional solidification, process improvement by introducing a strong magnetic field and the effects of substitute elements are described. Then, meaningful progress in mechanical properties, composite materials, the structural origin of magnetostriction based on ferromagnetic MPB theory and sensor applications are summarized. Furthermore, sintered composite materials based on the reconstruction of the grain boundary phase also provide new ideas for the development of magnetostrictive materials with excellent comprehensive properties, including high magnetostriction, high mechanical properties, high corrosion resistance and high resistivity. Finally, future prospects are presented. This review will be helpful for the design of novel magnetostrictive Tb-Dy-Fe alloys, the improvement of magnetostrictive and mechanical properties and the understanding of magnetostriction mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: The small additions of B and Cr can improve the room temperature ductility of Fe–Ga alloy. The (Fe81Ga19)99.5B0.5 sheets with thickness of 0.13–0.33mm were prepared by conventional rolling process and their magnetostriction property were investigated. Results demonstrated that under the same heat treatment, the magnetostriction of (Fe81Ga19)99.5B0.5 sheets increased with the decrease of deformation amount. The 0.33-mm-thick sheets have the peak magnetostrictive value of 129, 136 and 165ppm obtained at annealing condition of 1100, 1200 and 1300°C for 2h, respectively. Magnetostriction of (Fe81Ga19)99.5B0.5 annealed sheets was closely related to the recrystallization texture which depends on heat treatment process. The sheets with {100}〈012〉 texture exhibited higher magnetostrictive property than other sheets with {111}〈110〉 or {111}〈112〉 texture. [Copyright &y& Elsevier]

Spherical Fe–Ga particles were prepared by gas atomization. The Ga concentration of gas-atomized particles approached the nominal composition of Fe81Ga19. Most size fractions of particles had a polycrystalline structure. The main A2 phase and a DO3 phase emerged in the as-atomized powders. The L12 phase appeared in the annealed powders. Many single crystals were obtained due to grain growth during the thermal process. The maximum saturation magnetostriction of 6.4×10−5 was obtained in the composite containing the annealed powders. [Copyright &y& Elsevier]

Abstract: The addition of Nb could improve rolling ability of Fe81Ga19 alloy during rolling process. The (Fe81Ga19)99Nb1 sheet with thickness of 0.6mm was prepared by conventional hot rolling, warm rolling and cold rolling and its magnetostriction effects were studied. It demonstrates that the magnetostriction of the sheet is closely related to rolled texture, and the recrystallization texture depends on heat treatment process. The {111} and near {001}〈110〉 rolling-textures are major in the rolled sheet, and the magnetostriction λ ∥ only is about 26ppm. A near {011}〈100〉 texture and a {001}〈100〉 texture were formed in the recrystallized sheets which were quenched into water after 2h annealing at 1250°C and 1300°C, and their magnetostriction (3/2)λ RD are around 106ppm and 134ppm, respectively. [Copyright &y& Elsevier]

Abstract: Giant magnetostriction TbDyFe alloys, with 〈110〉 orientation and designated TDT-110, were prepared by a zone melting directional solidification technique with a high temperature gradient. Samples in the as-grown and heat-treated states, having various magnetostrictive properties, have been studied by transmission and scanning electron microscopy. The results of microscopy studies indicate that the density and distribution of microstructural defects substantially influence the magnetostrictive strains for these alloys. [Copyright &y& Elsevier]

Fe83Ga17 alloy ribbons with four thicknesses were prepared by the melt-spun method. The measured results show that magnetostriction is related to the thickness of the ribbons, and its maximum value, −2100 ppm, has been obtained in the ribbon with a thickness of 75 μm. The results of the X-ray diffraction (XRD) and the differential scanning caloric (DSC) show that a phase with DO3 structure emerges in those ribbons with the thicknesses of 45, 55 and 75 μm, and a phase transition of A2 + DO3 → A2 occurred at 669°C for the ribbon with the thickness of 75 μm. The increase in the cooling rate can restrain the precipitation of the Ga-rich phase in the ribbon. It is considered that the giant magnetostriction of ribbons originates from the A2 + special DO3 structure and shape magnetic anisotropy. [ABSTRACT FROM AUTHOR]

As a kind of magnetostrictive ceramics, cobalt ferrites are widely concerned because of its large magnetostriction and high resistivity, which are ideal for high-frequency applications. But, the high driving magnetic field due to the high magnetocrystalline anisotropy limits the practical applications of cobalt ferrites, thus, it is a still a challenge to find a balance between high magnetostriction properties and low driving magnetic fields. In this work, we investigated the effects of partially substitution of Ga3+ for Fe3+ on grain orientation and magnetic properties, attempting to maintain high magnetostriction while reducing the driving magnetic field. The CoFe 2-x Ga x O 4 (x=0, 0.05, 0.1, 0.15) with single-phase spinel structure were prepared by the conventional solid-state method. The saturation magnetization M S increased with the increase of Ga concentration, meanwhile the coercivity H c and magnetocrystalline anisotropy constant K 1 significantly decreased, which indicates the better soft magnetic characteristics of the Ga-doped cobalt ferrites. The oriented CoFe 2-x Ga x O 4 samples were obtained using magnetic field orientation technique during the powder forming process. The <001> preferred orientation was achieved in CoFe 2 O 4 samples. However, the <001> orientation degree decreased with the substitution of Ga, and the preferred orientation has changed into <111> at x=0.15. The Ga substitution affected the magnetocrystalline anisotropy and grain orientation, thereby affecting the magnetostrictive properties. As for the non-oriented samples, although the maximum magnetostrictive strain slightly decreased with Ga substitution, while there was a significant drop in the magnetostrictive saturation field. However, the magnetostriction of the oriented samples decreased significantly with the substitution of Ga due to the change of grain orientation from <001> to <111>. [ABSTRACT FROM AUTHOR]

Magnetostrictive Fe 82 Ga 4.5 Al 13.5 sheets with 0.1 at% NbC were prepared from directional solidified alloys with <0 0 1> preferred orientation. The slabs were hot rolled at 650 °C and warm rolled at 500 °C. Then some warm-rolled sheets were annealed intermediately at 850 °C for 5 min but the others not. After that, all the sheets were cold rolled to a final thickness of ∼0.3 mm. The microstructures, the textures and the distributions of second phase particles in the primary recrystallized samples were investigated. With intermediate annealing, the inhomogeneous microstructure was improved remarkably and strong Goss ({1 1 0}<0 0 1>) and γ-fiber (<1 1 1>//normal direction [ND]) textures were produced in the primary recrystallized samples. But, an evident disadvantage in size and quantity was observed for Goss grains in the primary recrystallized sample without intermediate annealing. After a final annealing, the final textures and magnetostrictions of samples with and without intermediate annealing were characterized. For samples without intermediate annealing, abnormal growth of {1 1 3} grains occurred and deteriorated the magnetostriction. In contrast, abnormal Goss grain growth occurred completely in samples with intermediate annealing and led to saturation magnetostriction as high as 156 ppm. [ABSTRACT FROM AUTHOR]

Alloys of Fe 82 Ga 18−x Al x (x=0, 4.5, 6, 9, 12, 13.5) were prepared by directional solidification technique and exhibited a <001> preferred orientation along the axis of alloy rods. The saturation magnetostriction value of the Fe 82 Ga 13.5 Al 4.5 alloy was 247 ppm under no pre-stress. The tensile properties of alloys of Fe 82 Ga 18−x Al x at room temperature were investigated. The results showed that tensile ductility of binary Fe-Ga alloy was significantly improved with Al addition. The fracture elongation of the Fe 82 Ga 18 alloy was only 1.3%, while that of the Fe 82 Ga 9 Al 9 alloy increased up to 16.5%. Addition of Al increased the strength of grain boundary and cleavage, resulting in the enhancement of tensile ductility of the Fe-Ga-Al alloys. Analysis of deformation microstructure showed that a great number of deformation twins formed in the Fe-Ga-Al alloys, which were thought to be the source of serrated yielding in the stress-strain curves. The effect of Al content in the Fe-Ga-Al alloys on tensile ductility was also studied by the analysis of deformation twins. It indicated that the joint effect of slip and twinning was beneficial to obtain the best ductility in the Fe 82 Ga 9 Al 9 alloy. [ABSTRACT FROM AUTHOR]

Abstract: In this paper five J–H curves, the magnetic polarization curves, which are come from five M–H curves, have been given. From these curves, by using the approaching saturation law, the anisotropy constants of corresponding alloys have been given. And the curve K 1–x has been got. The variation of the curve K 1–x has been discussed. [Copyright &y& Elsevier]

Abstract: 〈110〉 oriented rods of TbDyFe giant magnetostrictive alloy have been prepared by zone melting directional solidification method. Two steps heat treatments were performed at 1353K for 2h, followed by heating at 673, 773, 873, 973K for 4h in argon atmosphere and air cooling. The effect of a two steps heat treatment on the mechanical properties, fractography and magnetostriction of TbDyFe has been studied. It was found that the largest values of impact toughness, compression strength and magnetostriction were achieved when the alloy was heat-treated at 873K. Room temperature Vickers indentation was performed to access the fracture toughness, and with heating temperature increasing from 673 to 973K, the fracture toughness was gradually improved. The change of mechanical properties and magnetostriction of TbDyFe was due to a change of the relative dimensions and distribution of the rare earth-rich phase caused by the two steps heat treatment. [Copyright &y& Elsevier]

Effect of heat treatment on magnetostrictive properties and order-disorder transition of (110) -oriented polycrystal Fe83Ga17 alloys is investigated. It is found that magnetostriction and order degree of Fe83Ga17 alloys are very sensitive to cooling rate. Variation of magnetostriction is discussed in terms of order-disorder transition. Under compressive stress of 20 MPa, saturation strain λ3 of partially ordered Fe83Ga17 alloys quenched into water reaches 298 × 10-6. [ABSTRACT FROM AUTHOR]

Magnetostrictive materials with high magnetomechanical coupling performance are required for transducer design and tunable resonator applications. The magnetostriction of Fe-Ga and Co-Fe alloy can be remarkably increased by high-density and semicoherent nanoparticles. In this work, we found that the magnetomechanical coupling of Co 70 Fe 30 alloy can be obviously enhanced by high-density nanoprecipitation. This outstanding enhancement originates from the semicoherent face-centered tetragonal (fct) nanoparticles embedded in a body-centered cubic (bcc) matrix, which may promote magnetic domain rotations under applications of stress. The result indicates that high-density nanoprecipitation can be used to guide the design of magnetostrictive materials with unusual magnetomechanical coupling performance. • Magnetomechanical coupling of Co 70 Fe 30 alloy can be enhanced by fct nanoprecipitation. • fct nanoparticles in bcc matrix can reduce the stress required for domain rotation. • The ΔE effect as large as 50.2% can be achieved in bcc+fct structured Co 70 Fe 30 alloy. [ABSTRACT FROM AUTHOR]

The microstructure, magnetic and magnetostrictive properties as well as ultrasonic guided wave sensing performance of annealed Fe 81 Al 19 coatings prepared on 316L stainless steel by high velocity oxy-fuel spraying were investigated systematically. The maximum magnetostriction reaches 38 ppm with the coating annealed at 400 °C and the saturation magnetic field is <400 Oe. The phase transformation behavior of A2 → A2 + DO 3 occurs with the annealing temperature increases above 470 °C. Effects of annealing on texture and structural evolution and magnetic properties of the coating are also discussed. Based on magnetostrictive effect and Villari effect of Fe 81 Al 19 coating, the ultrasonic guided waves are actuated and detected successfully. With proper bias magnetic field, the amplitudes of echo signals can be enhanced in Fe-Al coating annealed at 500 °C. The corresponding (dλ/d H) max under a lower bias magnetic field indicates less eddy current loss and the optimal transduction. The deeper electromagnetic skin depth in the annealed coating results in a higher ultrasonic guided wave amplitude and improves the detection sensitivity in the electromagnetic acoustic transducers. This work exhibits the prospect of the magnetostrictive coatings in a range of potential applications, such as electromagnetic acoustical transducers used for non-destructive testing. Unlabelled Image • The magnetostrictive Fe 81 Al 19 coatings are fabricated by high velocity oxy-fuel spraying. • The phase transformation occurs at 470 °C during the post annealing temperature. • The maximum magnetostriction reaches 38 ppm in the annealed Fe 81 Al 19 coating. • Ultrasonic guided waves are obtained from magnetostrictive Fe-Al coating, which can be used in non-destructive testing. [ABSTRACT FROM AUTHOR]

We report the magnetostriction and 〈0 0 1〉 texture of anisotropic polycrystalline CoFe2O4. Slurries with well dispersion and low sintering shrinkage are aligned by the magnetic field of 2 T and sintered to prepare highly 〈0 0 1〉 textured CoFe2O4 samples. For the anisotropic sample, benefiting from the 〈0 0 1〉 fiber texture, a higher magnetostrictive property is achieved than that of isotropic polycrystalline sample prepared by dry compaction. The maximum magnetostriction up to −500 ppm at 1000 Oe is obtained, which reaches 85% of the highest value in single crystal (λ 100  = −590 ppm). Meanwhile, the maximum strain-field derivative is also improved to −0.97 ppm/Oe at 250 Oe, which is highly beneficial for sonar detector and force sensor applications. [ABSTRACT FROM AUTHOR]

The effects of different rolling conditions on the microstructure and texture of primary and secondary recrystallization in magnetostrictive Fe 82 Ga 9 Al 9 +0.1at%NbC alloy sheets were investigated. After the primary recrystallization annealing at 850 °C for 5 min, the as-rolled sheets prepared by warm-cold rolling with an intermediate annealing, can be fully recrystallized, and obtain the homogeneous matrix in which the fine dispersed NbC precipitate particles are distributed. The primary recrystallization textures of sheets with different rolling conditions consist mostly of strong {1 0 0} textures, γ-fiber textures, {4 1 1}〈1 4 8〉 texture and weak Goss texture. In the primary recrystallized sheets prepared by warm-cold rolling with an intermediate annealing, the high energy grain boundaries and ∑9 boundaries have the highest proportion. After high temperature annealing, the secondary recrystallizations of Goss grains in these sheets are more complete, and the size of abnormal grown Goss grain is up to several centimeters, which results in the strongest Goss texture. Correspondingly, the largest magnetostriction of 183 ppm is observed. The sample prepared by warm-cold rolling with an intermediate annealing, has homogeneous primary matrix, special texture components and grain boundary distribution, all of which provide a better surrounding for the abnormal growth of Goss grains. This work indicates that the control of rolling conditions of Fe-Ga-Al alloy sheets is necessary to achieve the strong Goss texture and obtain a possible high magnetostriction if other appropriate conditions (stress, domain structure) are achieved. [ABSTRACT FROM AUTHOR]

In this work, on the basis of multiphase characterics of near Ga-27 at.% alloy, magnetic field annealing was applied in a directional solidification (DS) 〈001〉 oriented Fe 73 Ga 27 polycrystalline alloy, and the saturation magnetostriction of 370 ppm under low magnetic field has been achieved. Large numbers of multiphase nanoparticles are precipitated in this process; also the magnetic heterogeneities are used to enhance magnetostriction. Meanwhile, this method provides an approach for developing excellent magnetostrictive materials. [ABSTRACT FROM AUTHOR]

In this work, 〈1 0 0〉 textured Co 70 Fe 30 alloy was successfully prepared by directional solidification technique. The effect of heat treatment on magnetostriction and microstructure of Co 70 Fe 30 alloy has been investigated. The Co 70 Fe 30 alloy was annealed in argon atmosphere at 700 °C–900 °C for 9 days and then cooled to room temperature by slow cooling or quenching. The magnetostriction as large as 180 ppm has been achieved for the quenched samples when the annealing temperature is ranging from 820 °C to 860 °C. Structural analyses indicate that the large magnetostriction originates from precipitation of a nanoscale face-centered tetragonal (fct) phase embedded in a body-centered cubic (bcc) phase matrix. [ABSTRACT FROM AUTHOR]

A great number of fine and dispersive NbC precipitates were obtained in Fe 82 Ga 4.5 Al 13.5 sheets by rolling process consisting of hot rolling at 900 °C, warm rolling at 500 °C and intermediate annealing at 650 °C for 15 min. The mean size of precipitates in primarily recrystallized sheets is ∼45 nm. Grain growth in final sheets was investigated to study the influence of fine precipitates on the promotion of abnormal grain growth (AGG). Fully developed AGG of Goss grain was observed in samples with the heating rate during continuous process of 0.5 °C/min, 1 °C/min and 2 °C/min. In contrast, AGG in samples of 0.25 °C/min and 4 °C/min were partially developed. The influence of heating rate on the development of AGG was examined by the investigation of precipitates and grain configurations during continuous heating process. With the fine precipitates, sharp Goss orientation was developed in Fe 82 Ga 4.5 Al 13.5 sheets annealed at Ar atmosphere. A maximum saturation magnetostriction of 170 ppm was obtained in sample of 2 °C/min. [ABSTRACT FROM AUTHOR]

Fe 82 Ga 13.5 Al 4.5 wires of 0.5 mm diameter were successfully prepared by heat forging, rolling, and combining hot and cold drawing. The 〈110〉 texture and A2 phase with 692.3 °C Curie temperature were observed in the as-drawn and 5A alternating current annealed (AC-annealed) wires. A large Wiedemann twist of 222.6″/cm was obtained at 1350 A/m axial magnetic field ( H a ) and 1400 A/m circumferential magnetic field ( H c ) in the AC-annealed wire, which could be attributed to the relatively large magnetostriction of − 46.2 ppm in the perpendicular direction. For displacement sensors application based on the Wiedemann effect at high temperatures, the propagation speed of the torsional wave in Fe 82 Ga 13.5 Al 4.5 wire was studied. A linear downward trend with rising temperature was observed which was related to the decreases in elastic modulus that resulted by thermal expansion. This work shows that Fe 82 Ga 13.5 Al 4.5 wire should be an ideal material for displacement sensors application over wide temperature range; nevertheless, for the measurement accuracy, the velocity of torsional wave should be set consistent with ambient temperature. [ABSTRACT FROM AUTHOR]

In this work, 0.5 mm diameter magnetostrictive (Co 70 Fe 30 ) 99.8 (NbC) 0.2 wires were prepared using forging and drawing processes. A Wiedemann twist up to 1348″/cm has been achieved in the annealed wires and to our knowledge is the largest value of Wiedemann effect in magnetoelastic materials. Microstructure analyses of the annealed wires indicate that large Wiedemann twist was attributed to the 〈100〉 circumferential texture and the fcc nanoparticles embedded in bcc matrix. The results indicate that the favorable circumferential texture and heterogeneous structure can be used to guide exploration of materials with large Wiedemann effect. [ABSTRACT FROM AUTHOR]

Elastic modulus of magnetic materials tends to increase with temperature rising, as the result of gradual loss of magnetic order with approaching Curie point. In this work, the similar behavior was also observed in the directional solidified Fe 73 Ga 27 alloy along the <100> preferred orientation. However, unlike the previous theory, results of magnetic-temperature and thermal expansion measurements show the absence of magneto-volume effect. Such unusual behavior of Young's modulus could be attributed to the enrichment of diffusing atoms along the direction of lowest modulus during the phase transition of A2 → D0 3 . According to the analysis of in situ heating XRD and TEM, the structure transitions of A2 → D0 3 → A1 → L1 2 were identified in the temperature range 20–500 °C, which correspond exactly to the changes of Young's modulus in both as-cast and directional solidified samples. [ABSTRACT FROM AUTHOR]

The secondary recrystallization behavior with temperature increasing from 900 to 1080 °C was investigated in the rolled columnar-grained magnetostrictive Fe–Ga alloy sheets. The abnormal Goss grain growth occurred due to the inhibitory action of NbC in the Fe–Ga–0.1 at%NbC sheets. With the temperature increasing at a rate of 0.25 °C/min, the secondary recrystallization started below 950 °C. In addition to the S-induced surface energy effect, sulfur annealing also introduced a large number of S-rich and Nb-rich precipitates, which retarded the grain boundary migration on the surface. The abnormal grain growth was found to be restricted inside the sheet during the sulfur annealing process when the temperature was below 1000 °C, and a large amount of small island-like grains was remained on S-annealed sheets. After final Ar/H 2 annealing processes, the S-rich precipitates and small island-like grains were eliminated, and sharp Goss orientation and high magnetostriction of 245 ppm were obtained in the final S-annealed sheets. [ABSTRACT FROM AUTHOR]

Sintered Tb-Dy-Fe materials prepared by the compression molding method have higher relative density and energy density than powder-bonded composites. However, due to the low magnetocrystalline anisotropy and the cubic symmetry of the Laves structure, the orientation degree of sintered materials is relatively low and not beneficial for obtaining large magnetostriction. We prepared the sintered Tb-Dy-Fe/DyCu compacts with preferred <111 > orientation by applying magnetically oriented powder metallurgy. The dependence of orientation degree and magnetostriction of oriented Tb-Dy-Fe/DyCu sintered compacts on different particle morphology and Tb/Dy ratios were studied. The oriented Tb-Dy-Fe/DyCu sintered compacts prepared from the milled single crystal Tb-Dy-Fe powders gained a higher <111 > orientation due to the small rotational resistance when magnetic particles move in a magnetic field, achieving improved magnetostriction. Magnetocrystalline anisotropy which determines the rotational torque caused by the magnetic field is one of the important factors affecting the rotation behavior of magnetic particles in a magnetic field. We designed Tb-Dy-Fe alloys with different Tb/Dy ratios which have different magnetocrystalline anisotropy, and prepared the sintered Tb-Dy-Fe/DyCu compacts under the same process parameters. The magnetocrystalline anisotropy constant K 1 of Tb x Dy 1-x Fe 1.95 (x = 0.27, 0.30, 0.33, 0.50) alloys increased from 0.66 × 106 J/m3 to 3.85 × 106 J/m3 by raising the Tb/Dy ratios, and the <111 > orientation degree of sintered Tb-Dy-Fe/DyCu compacts was promoted simultaneously. The oriented Tb 0.33 Dy 0.67 Fe 1.95 /DyCu sintered compact achieved the highest <111 > orientation degree of 56.6%, resulting in the largest magnetostriction of 1326 ppm and the d 33 peak value of 6.81 nm/A. [Display omitted] • The near-spherical Tb-Dy-Fe particles improve the <111> orientation degree. • The <111> orientation degree promoted by raising Tb/Dy ratios of Tb-Dy-Fe alloys. • The higher <111> orientation degree resulted in higher magnetostriction. • The low-field magnetostrictive performance was attributed to moderate K 1 value. [ABSTRACT FROM AUTHOR]

In this work, the 〈1 0 0〉 directional solidified feedstock slabs were used to produce the rolled Fe–Ga sheets, and sharp Goss orientation was developed in the 0.3 mm sheets after annealing processes. The area fraction of Goss grains in the annealed binary Fe–Ga sheets approached to 62.4% without abnormal grain growth, accompanied with a maximum magnetostriction ( λ // − λ ⊥ ) of 199 ppm. The addition of only 0.1 at% NbC notably promoted the abnormal Goss grain growth without sulfur annealing, and large single-crystal-like grains, up to several centimeters, were obtained with few island-like grains after sulfur annealing and final Ar/H 2 annealing processes. High magnetostriction ( λ // − λ ⊥ ) of 245 ppm with little deviation was achieved in the (Fe 83 Ga 17 ) 99.9 (NbC) 0.1 sheets, and a large magnetostrictive strain ( λ // ) up to 243 ppm under no pre-stress was observed with an applied magnetic field along the rolling direction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cubic texture was obtained in the thin sheet annealed at 1200 ℃ for 2 h. • The maximum magnetostriction was 145 ppm in the annealed thin sheet. • SH-mode magnetostrictive ultrasonic guide waves are obtained from the thin sheet. • Suitable annealing process facilitates magnetostrictive detected sensitivity. Based on the ultrasonic guided wave detection technique, the effects of the annealing process on the microstructures, properties, and ultrasonic guided wave transduction performances of (Fe 83 Ga 17) 99.9 (NbC) 0.1 thin sheets with thicknesses ranging from 0.06 mm to 0.15 mm for magnetostrictive guided wave sensors in non-destructive testing were investigated. The results demonstrated that in contrast to the texture formed when annealing under an Ar atmosphere, the {1 0 0} 〈0 0 1〉 texture formed in the recrystallized Fe-Ga thin sheets annealed with a flowing Ar/H 2 gas mixture, resulting in a saturation magnetostriction of 145 ppm. This might have been related to the influence of the strain recrystallization rate, stored energy, and surface energy. The proposed magnetostrictive guided waves could be used for inspection using the thin sheets. In particular, the thin sheet annealed at 1200 °C for 2 h exhibited excellent guided wave sensing characteristics. This was mainly attributed to the formation of a cubic texture and the value of (dλ/d H) max corresponded to a lower-bias magnetic field. This demonstrated that a proper annealing treatment improved not only the texture but also the sensitivity for guided wave detection. Therefore, this work demonstrated the prospects of applying (Fe 83 Ga 17) 99.9 (NbC) 0.1 thin sheets for ultrasonic guided wave detection. [ABSTRACT FROM AUTHOR]

The influence of annealing process, including heating rate and final annealing atmosphere, on texture evolution and magnetostrictive performance of rolled 0.16wt% NbC doped Fe–Ga sheets has been investigated. It demonstrates that texture evolution is closely related with heating rate, and strong Goss texture {110}〈001〉 was obtained at 0.25°C/min after the heating process from 900°C to 1080°C, accompanied with a peak value of saturation magnetostriction. Non-Goss texture and deviation from ideal {110}〈001〉 were observed at lower or higher heating rate, resulting in the decrease in saturation magnetostriction. Compared with pure-Ar annealed sheets, the hydrogen introduced into annealing atmosphere during final treatment promoted (110) grain growth and eliminated the Nb-rich precipitates, and additional improvement in the saturation magnetostriction was observed for the same annealing protocols, with a maximum measured value, (3/2)λs=λ //−λ ⊥ , of 233×10−6 obtained in the final Ar/H2 annealed sheet. [ABSTRACT FROM AUTHOR]

In contrast to the disordered body-centered cubic (bcc) A2 phase, the ordered face-centered cubic (fcc) L1 2 phase exhibits negative magnetostriction (λ) and has a high elastic modulus (E). Therefore, an in-depth understanding of the microstructural evolution of Fe–Ga thin films from bcc A2 phase to fcc L1 2 phase is essential to obtain Fe–Ga thin films with desirable properties. The transformation of the phase structure, magnetic domain structure, and magnetic properties of Fe 72 Ga 28 thin films is analyzed in this study. The phase transformation of the Fe 72 Ga 28 thin film from A2 to A2 L1 2 occurred after heat treatment, as determined by high-resolution transmission electron microscopy (HRTEM) and glancing-incidence X-ray diffraction (GI-XRD). Non-continuous lattice distortion at the phase boundaries of A2 and L1 2 was also observed, as shown by geometric phase analysis (GPA) and electron backscattered scattering detection (EBSD). Numerous edge dislocations at the phase boundaries were revealed by HRTEM. A shift in the magnetic domain structure from the maze-like domain to maze-like domain and honeycomb-like domain was detected by magnetic force microscopy (MFM). The variation in magnetic properties was determined to be related to the structural transformation and ununiform lattice distortion between the phase boundaries of the A2 and L1 2. • The A2 to A2+L1 2 transition in annealed Fe 72 Ga 28 thin films is proved. • The largest lattice distortion is discontinuous along the phase boundaries of the A2 and L1 2 phases. • The lattice distortion of the L1 2 phase is not uniform, unlike that of the A2 phase. • Magnetic domain of annealed Fe 72 Ga 28 thin films changed from maze-like domain to maze-like domain and honeycomb-like domain. • The effects of structural transformation and lattice distortion on the magnetic properties of the films are evaluated. [ABSTRACT FROM AUTHOR]

Abstract: The Tb0.29(Dy1−x Pr x )0.71Fe1.97 (x=0, 0.1, 0.2 and 0.3) alloys were prepared by directional solidification method. The orientation, magnetostriction λ, Curie temperature T c and microstructure of alloys were characterized by XRD, standard resistant strain gauge technique, VSM and SEM-EDS. The results reveal that the alloys have a preferred orientation of 〈110〉 and 〈113〉 direction when x>0. With the increase in Pr content, the T c of alloys decreases gradually and the non-cubic phase appears, resulting in the decline of λ dramatically, from 1935.2×10−6 for x=0 to 695.9×10−6 for x=0.3 at a compressive stress of 6MPa and a magnetic field of H=240kAm−1. [Copyright &y& Elsevier]

Tb-Dy-Fe alloy has been regarded as a giant magnetostrictive material and used in applications such as actuators and sensors. However, the brittleness of Laves phase in Tb-Dy-Fe alloy, resulting in the fracture failure during machining operations and the cracking failure for the material in service, significantly decreases its engineering design and applications. This study aims to investigate the effect of restructuring the grain boundary phases of Tb-Dy-Fe alloy by diffusing low-melting-point alloys. The low-melting-point Dy–Cu alloys were diffused into Tb 0.3 Dy 0.7 Fe 1.95 alloy ingot by different heat-treatments. The microstructure, magnetostrictive properties, fracture behavior and bending strength were studied systematically. The ductile (Dy,Tb)Cu phase has been produced to substitute for RE-rich phase in grain boundary. The results indicated that magnetostriction remained at a high value (1021–1448 ppm) after diffusion. However, the mechanical property improved significantly, which was attributed to massively formed ductile (Dy,Tb)Cu phase in grain boundary. Compared with the non-diffused alloy with bending strength of 43–48 MPa, the bending strength of Tb 0.3 Dy 0.7 Fe 1.95 alloy with diffusing DyCu alloy at 1000 °C increased to 74 MPa, and the best bending strength of Tb 0.3 Dy 0.7 Fe 1.95 alloy with diffusing DyCu 2 alloy at 1000 °C increased to 115 MPa. Image 1 • Introducing (Dy,Tb)Cu phase into GB improves the bending strength to 115 MPa. • Diffusion alloys with more Cu can raise toughness (Dy,Tb)Cu phase content in GB. • Forming toughness phase in GB remains high value of magnetostriction. [ABSTRACT FROM AUTHOR]