Rapid solidification and magnetism characteristics of Co-11.8 at%Gd and Co-7.5 at%Gd dual-magnetic ribbons at different wheel speeds

The rapidly solidified ribbons of Co-7.5 and 11.8 at%Gd alloys were obtained by the melt spinning technique. The magnetic properties were measured and the effects of the wheel speed and the heat treatment on the coercivity were examined. SEM and EDS results show that the microstructures of melt-spun ribbons vary at different wheel speeds and after the heat treatment (1073 K, 30 min), and the soft magnetic properties of annealed ribbons are better than those of quenched ones. For Co-11.8 at%Gd ribbons, the maximum saturation magnetization reaches to 65.11 emu/g at the wheel speed of 20 m/s, while the minimum value of coercivity is 75.32 Oe. For Co-7.5 at%Gd ribbons, the minimum value of coercivity is 43 Oe in the annealed ribbons at 30 m/s and the maximum value of saturation magnetization is 106.93 emu/g from the annealed ribbons at 40 m/s. Theoretical analysis indicates that the exchange coupling length of (Co) and Co₁₇Gd₂ phases is 65.3 nm, and the exchange coupling coefficient of Co-7.5 and 11.8 at%Gd ribbons is in the range of 0.023–0.089. The exchange coupling effect in Co-11.8 at%Gd ribbons is stronger than that in Co-7.5 at%Gd ribbons.     

Influence of wheel speed during planar flow melt spinning on the microstructure and soft magnetic properties of Fe<Subscript>68.5</Subscript>Si<Subscript>18.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons

The structure and soft magnetic properties of Fe_68.5Si_18.5B₉Nb₃Cu₁ (at.%) alloy ribbons produced through planar flow melt spinning at different wheel speeds viz. 34, 17 and 12 m/s have been investigated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, vibrating sample magnetometer and positron lifetime spectroscopy. Amorphous ribbons formed with different wheel speeds manifested different enthalpy and activation energy of crystallization. The volume fraction of nanocrystalline phase, saturation magnetization and permeability are found to increase whereas coercivity is found to decrease with increasing wheel speed on annealing. A detailed analysis of positron lifetime spectra obtained from the as-spun ribbons has been used to rationalize the variation in microstructure and magnetic properties. The presence of larger number of defects at higher wheel speed increases the volume fraction of nanocrystalline phase on annealing which improves the soft magnetic properties.     

Grain boundary migration in Fe-3mass%Si alloy bicrystals with twist boundary

Abstract

The characteristics of grain boundary migration in Fe-3mass%Si alloy bicrystals with ∑3(011), ∑5(001) and ∑9(011) coincidence twist boundaries and random twist boundaries were examined to obtain an information on the development of {110}(001) (Goss) texture. The bicrystals were annealed at 1223 K for an appropriate time and the grain boundary migration speed was evaluated.

The ∑5 001l and ∑9 011l twist boundaries showed higher migration speed than ∑3(011) twist boundaries, and the random twist boundaries migrated faster than other boundaries. The migration speed decreased with increasing annealing time due to an increase in the edge components of the lattice misfits in the migrated boundaries. The grain boundary migration was also sensitive to the deviation angle (?θ) from the ideal orientation relationship for a coincidence boundary. The increase of ?θ accelerated the boundary migration. The motion of the grain boundary was influenced by plastic strain. Migration of the ∑9 twist boundary was more suppressed by plastic strain than that of the random boundary. On the basis of characteristics of the grain boundary migration, the effect of inhibitor on the Goss texture was discussed. © 2000 Elsevier Science Ltd. All rights reserved.     

Grain size dependence of coercivity and permeability innanocrystalline ferromagnets

Amorphous ribbons of composition Fe_74.5-xCu_xNb₃Si_13.5B₉ (x=0, 1 at.%) have been annealed between about 500°C and 900°C. This produced a series of crystallized samples with grain sizes between about 10 nm and 300 nm and with coercivities H _c and initial permeabilities μ_i varying over several orders of magnitude. The best soft magnetic properties (H _c≈0.01 A/cm and μ_i≈80×10³ ) were observed for the smallest grain sized of about 10 nm. With increasing grain size D, coercivity steeply increases following a D⁶-power law (up to D≈50 nm). H_c then runs through a maximum of H_c≈30 A/cm and decreases again for grain sizes above 150 nm according to the well-known 1/D law for polycrystalline magnets. The initial permeability was found to vary in a similar manner, essentially being inversely proportional to coercivity. The variation of the soft magnetic properties with the average grain size is discussed and compared with the predictions of the random anisotropy model and other theories for the magnetization reversal     

The microstructure and magnetic properties of NdFeB magnets directly solidified at a low cooling rate

Nd_12.5Fe₈₂B_5.5 ribbons have been prepared by a melt spinning technique at a wheel speed ranging from 5 to 22 m/s. It was found that the wheel speed v_R dramatically influences the microstructure and magnetic properties of the ribbons. At an optimized v_R, a structure with single-phase Nd₂Fe₁₄B and an enhanced coupling between grains give rise to excellent magnetic properties. For example, the coercivity, remanence ratio, and maximum energy product of the best sample quenched at a wheel speed of 13 m/s are 1227.4 kA/m, 0.76, and 182.6 kJ/m³, respectively. In comparison with the samples from under- and over-quenched conditions and all the samples with annealing, the as-quenched sample fabricated at the optimized wheel speed has the best magnetic properties.     

Large electrical resistivity and high saturation magnetization nanocrystalline Fe86B13Cu1 alloy prepared by hot isothermal pressing

The effects of hot isothermal pressing (HIP) on the microstructures and magnetic properties of nanocrystalline Fe₈₆B₁₃Cu₁ ribbons were studied. It is shown that the precipitation of Fe₃B phase is suppressed and the grain size of α-Fe phase decreases to 13.2 nm when amorphous Fe₈₆B₁₃Cu₁ ribbons are annealed by HIP under the pressure of 150 MPa. A high electrical resistivity and high saturation magnetization nanocrystalline soft magnetic material is prepared by HIP owing to the suppression of the precipitation of Fe₃B phase and a marked decrease in the grain size of α-Fe phase. The prepared sample exhibits a large electrical resistivity of 183 μΩ cm, a high saturation magnetization of 1.94 T and a low coercive force of 12 A/m.     

Magnetic orientation and magnetic anisotropy in paramagnetic layered oxides containing rare-earth ions

Abstract

The magnetic anisotropies and easy axes of magnetization at room temperature were determined, and the effects of rare-earth (RE) ions were clarified for RE-based cuprates, RE-doped bismuth-based cuprates and RE-doped Bi-based cobaltite regarding the grain orientation by magnetic field. The easy axis, determined from the powder orientation in a static field of 10 T, depended qualitatively on the type of RE ion for all three systems. On the other hand, the magnetization measurement of the c-axis oriented powders, aligned in static or rotating fields, revealed that the type of RE ion strongly affected not only the directions of the easy axis but also the absolute value of magnetic anisotropy, and an appropriate choice of RE ion is required to minimize the magnetic field used for grain orientation. We also studied the possibility of triaxial grain orientation in high-critical-temperature superconductors by a modulated oval magnetic field. In particular, triaxial orientation was attempted in a high-oxygen-pressure phase of orthorhombic RE-based cuprates Y₂Ba₄Cu₇O_y. Although the experiment was performed in epoxy resin, which is not practical, in-plane alignment within 3° was achieved.     

Relationship between microstructure and magnetic domain structure of Nd--Fe--B melt-spun ribbon magnets

The relation between the microstructure, observed using an electron probe microanalyzer, and the domain structure, observed using a Kerr microscope, was established to evaluate the effects of hot rolling and the addition of Ti--C on the c-axis orientation and the magnetization process of hot-rolled Nd--Fe--B--Ti--C melt-spun ribbons. The addition of Ti--C promotes the c-axis orientation and high coercivity in the ribbons. Elemental mapping suggests a uniform elemental distribution; however, an uneven distribution of Ti was observed in an enlarged grain with Ti-enriched points inside the grain. The reversal domains that nucleated at the Ti-enriched point inside the grain cause low coercivity.     

Magnetic orientation and magnetic anisotropy in paramagnetic layered oxides containing rare-earth ions

The magnetic anisotropies and easy axes of magnetization at room temperature were determined, and the effects of rare-earth (RE) ions were clarified for RE-based cuprates, RE-doped bismuth-based cuprates and RE-doped Bi-based cobaltite regarding the grain orientation by magnetic field. The easy axis, determined from the powder orientation in a static field of 10 T, depended qualitatively on the type of RE ion for all three systems. On the other hand, the magnetization measurement of the c-axis oriented powders, aligned in static or rotating fields, revealed that the type of RE ion strongly affected not only the directions of the easy axis but also the absolute value of magnetic anisotropy, and an appropriate choice of RE ion is required to minimize the magnetic field used for grain orientation. We also studied the possibility of triaxial grain orientation in high-critical-temperature superconductors by a modulated oval magnetic field. In particular, triaxial orientation was attempted in a high-oxygen-pressure phase of orthorhombic RE-based cuprates Y₂Ba₄Cu₇O_y. Although the experiment was performed in epoxy resin, which is not practical, in-plane alignment within 3° was achieved.     

Magnetic properties, phase evolution, and microstructure of melt spun Hf-substituted Sm(Co0.97Hf0.03)(x)Cy (x = 5-9; y = 0-0.1) nanocomposites

Magnetic properties, phase evolution, and microstructure of melt spun Hf-substituted Sm(Co0.97Hf0.03)(x)Cy (x = 5-9; y = 0-0.1) ribbons quenched at the wheel speed of 40 m/s are investigated. X-ray diffraction analysis shows that the main phases existed in Sm(Co0.97Hf0.03)(x) ribbons are 1:5 phase for x = 5-5.5; 1:5 and 1:7 phases for x = 6; 1:7 phase for x = 6.5-7.5; 1:7 and 2:17 phases for x = 8; and only 2:17 phase for x = 8.5-9, respectively. For Sm(Co0.97Hf0.03)(x) (x = 5-9) ribbons, the optimum magnetic properties of B(r) = 5.6 kG, (i)H(c)= 15.6 kOe and (BH)(max) = 7.1 MGOe are obtained for Sm(Co0.97Hf0.03)6.5 ribbons. Furthermore, a slight amount of C addition in Sm(Co0.97Hf0.03)(x) ribbons slightly modify phase constitution and effectively refine the grain size from 200-700 nm for C free ribbons to 10-70 nm, strengthening the exchange coupling effect between magnetic grains of the ribbons. As a result, magnetic properties are further improved. The magnetic properties of B(r) = 6.9 kG, (i)H(c) = 9.2 kOe and (BH)(max) = 10.0 MGOe can be achieved for Sm(Co0.97Hf0.03)7.5C0.1 nanocomposites.     

Grain boundary migration in Fe-3mass%Si alloy bicrystals with twist boundary

The characteristics of grain boundary migration in Fe-3mass%Si alloy bicrystals with Σ3〈011〉, Σ5〈001〉 and Σ9〈011〉 coincidence twist boundaries and random twist boundaries were examined to obtain an information on the development of {110}〈001〉 (Goss) texture. The bicrystals were annealed at 1223 K for an appropriate time and the grain boundary migration speed was evaluated.The Σ5〈001〉 and Σ9〈011〉 twist boundaries showed higher migration speed than Σ3〈011〉 twist boundaries, and the random twist boundaries migrated faster than other boundaries. The migration speed decreased with increasing annealing time due to an increase in the edge components of the lattice misfits in the migrated boundaries. The grain boundary migration was also sensitive to the deviation angle (Δθ) from the ideal orientation relationship for a coincidence boundary. The increase of Δθ accelerated the boundary migration. The motion of the grain boundary was influenced by plastic strain. Migration of the Σ9 twist boundary was more suppressed by plastic strain than that of the random boundary. On the basis of characteristics of the grain boundary migration, the effect of inhibitor on the Goss texture was discussed.     

Effect of Oxygen Content on Grain Growth Kinetics of Titanium

The grain growth kinetics of commercially pure Titanium with different contents of oxygen have been studied. The grain size parameters have been measured by means of the Image Analysis Technique for different heat treatment temperatures and times. The growth exponents and activation energies have been calculated. Finally, tensile tests on the same materials have been carried out. When the interstitial oxygen content in titanium increases the grain growth kinetics and the ductility decrease and the transition temperature, activation energy for grain growth and mechanical strength increase.     

Effect of external magnetic field on the deposition of BaFe12O19

The contribution of an external magnetic field on the deposition of BaFe₁₂O₁₉ thin film was investigated. For this purpose, two (one with applied field and another without field) thin films of BaFe₁₂O₁₉ were deposited on the C-plane oriented sapphire (Al₂O₃) substrate employing pulsed laser deposition technique. Crystallographic orientation and texture were determined using an X-ray diffractometer. The magnetic parameters were deduced from a vibrating sample magnetometer (VSM). A spectrometer was used to study the optical properties of the films. The structural results reveal the film to be predominantly single phase with C-plane orientation in both the cases. The film deposited with field, however, has bigger grain size and more perfection in crystallinity. The magnetic parameters show that the film deposited with the field has more remanence magnetization and higher coercive field. The diffuse reflectance of the film deposited with field is much higher due to the increased grain size and roughness.     

La2Fe14B和Ce2Fe14B合金在快淬和热处理过程中相析出行为的比较

研究了溶体快淬三元La_2Fe_(14)B和Ce_2Fe_(14)B合金的相析出行为和磁性能,对不同快淬速度(10~50 m/s)和不同热处理温度下制备的样品进行了系统分析。结果表明,通过直接快淬,La_2Fe_(14)B合金中不能形成2∶14∶1硬磁相,而Ce_2Fe_(14)B合金可以获得2∶14∶1相。La_2Fe_(14)B合金在10m/s快淬时主要由La和α-Fe相组成,而Ce_2Fe_(14)B合金中2∶14∶1硬磁相在10m/s和20m/s快淬时析出。随着辊速的增加,非晶相逐渐增多并成为主相。在热处理过程中,La_2Fe_(14)B合金析出相以α-Fe和La相为主,并且高温下液态的富La相和α-Fe相可以共存;而Ce_2Fe_(14)B合金中先析出α-Fe,后析出2∶14∶1硬磁相,随后析出相长大。结果还表明,La_2Fe_(14)B比Ce_2Fe_(14)B有更高的非晶居里温度和更低的α-Fe相析出温度。由于硬磁相的析出,Ce_2Fe_(14)B合金可以获得较好的硬磁性能,包括一定的矫顽力。此研究对含La、Ce稀土永磁材料的生产具有一定的指导作用。     

Grain coarsening mechanism of Cu thin films by rapid annealing

Cu thin films have been produced by an electroplating method using nominal 9N anode and nominal 6N CuSO₄·5H₂O electrolyte. Film samples were heat-treated by two procedures: conventional isothermal annealing in hydrogen atmosphere (abbreviated as H₂ annealing) and rapid thermal annealing with an infrared lamp (abbreviated as RTA). After heat treatment, the average grain diameters and the grain orientation distributions were examined by electron backscattering pattern analysis. The RTA samples (400 °C for 5 min) have a larger average grain diameter, more uniform grain distribution and higher ratio of (111) orientation than H₂ annealed samples (400 °C for 30 min). This means that RTA can produce films with coarser and more uniformly distributed grains than H₂ annealing within a short time, i.e. only a few minutes. To clarify the grain coarsening mechanism, grain growth by RTA was simulated using the phase field method. The simulated grain diameter reaches its maximum at a heating rate which is the same order as that in the actual RTA experiment. The maximum grain diameter is larger than that obtained by H₂ annealing with the same annealing time at the isothermal stage as in RTA. The distribution of the misorientation was analyzed which led to a proposed grain growth model for the RTA method.     

Grain size and texture effect on compression behavior of hot-extruded Mg–3Al–1Zn alloys at room temperature

Hot-extruded AZ31 alloy was subjected to compression at room temperature. The influence of grain size and grain orientation on the compression behavior of the specimens was examined by optical microscopy, compression test and X-ray diffraction. Abundant twins activated during compression of extruded AZ31 magnesium alloy. The hot extruded AZ31 magnesium alloys had a higher Hall–Petch slope for compression than that for tension.     

Fe77Co2Zr9B10Cu2合金的制备及其磁性能

采用单辊快淬法制备了Fe77Co2Zr9B10Cu2合金,在530～750℃等温退火40 min,利用X射线衍射和振动样品磁强计研究了Fe77 Co2 Zr9 B10 Cu2合金的微观结构和磁性能。结果表明:淬态Fe77Co2Zr9B10Cu2合金为非晶、纳米晶双相结构。随着退火温度的升高,α-Fe晶体相从非晶、基体中析出,晶粒尺寸长大,晶化体积分数增加,矫顽力先减小后增大,比饱和磁化强度逐渐增大。实验结果表明,530℃退火后合金的矫顽力最小,在670℃时迅速增大。样品的磁性与其微观结构、晶粒尺寸、晶化体积分数等因素有关.     

C49-TiSi2 epitaxial orientation dependence of C49-to-C54 phase transformation rate

We investigated the C49-TiSi₂ epitaxial orientation dependence of the C49-to-C54 phase transformation rate for samples with different pre-amorphizing As implantation (PAI) conditions. The C49 epitaxial orientation to the Si(001) substrate is characterized on the basis of the (131) rocking curves obtained from grazing-incidence X-ray diffraction (GIXD) measurements. We found that the phase transformation rate increases with decreasing C49 epitaxial orientation, and this dependence is very sensitive for the samples with PAI. For comparison with the orientation dependence, the C49 grain size dependence was also examined. The C49 grain size distributions were obtained from transmission electron microscope (TEM) images. Although the phase transformation rate seems to roughly increase with increasing C49 grain size, it does not show a clear relationship. Therefore, we conclude that the C49-to-C54 phase transformation rate is largely determined by the C49 epitaxial orientation, although the effects of C49 grain size and the density of As-ions cannot be ignored for the PAI process.     

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel

Abstract

Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 10⁶ primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model.     

温度对钛合金TB6显微组织和晶粒度的影响

通过对近β钛合金TB6进行不同温度热处理，研究了各温度下其显微组织和晶粒度大小变化。研究结果表明：钛合金TB6的最佳热处理温度为790℃，在此温度下进行热处理，可以获得较好的显微组织形态且β相可以达到95％左右；晶粒度比较均匀且达到等轴状态，晶粒度为4～4．5级。