Magnetostriction trend of non-oriented 6.5% Si–Fe

Non-oriented electrical steel is produced in strip form typically 0.35–1.0 mm thick and containing 0–3 wt% silicon. It is well-known that non-oriented electrical steel is not quite isotropic but has small anisotropy. In the last decade, NKK produced 0.1 mm thick, non-oriented steel 6.5% Si which has applications such as in high-frequency transformer due to its high electrical resistivity, low core losses, near zero magnetostriction, and high permeability. The magnetostriction of 6.5% silicon steel samples with dimensions 280 mm×30 mm×0.1 mm was measured when magnetised sinusoidally between 0.5 and 1.0 T at frequencies between 0.5 and 6 kHz. Test samples were clamped at one end and the peak-to-peak displacement of the free end was measured with the aid of the single-point laser vibrometer. The average peak–peak magnetostriction was 0.2–0.25 με apart from a sharp rise to 1.2 με at 2 kHz magnetising frequency. This agrees well with the predicted value of 2 kHz for l=0.28 m, d=7430 kg/m³ and E=166 GPa. This shows that although the 6.5% silicon steel is often thought of as having near zero magnetostriction, care is needed to avoid lamination lengths corresponding to resonance points which could induce higher noise in laminated cores.     

Influence of shearing process on domain structure and magnetic properties of non-oriented electrical steel

The influence of shearing on the magnetic properties and domain structure of 0.5 mm thick non-oriented electrical steel was studied. In the region from 1 to 1.4 mm from the sheared edge, a striped domain pattern that indicated the existence of elastic strain was observed. From the degradation tendency of flux density with respect to shearing width, the width of the degraded region near the edge increased as the magnetic field decreased. These results suggested that the change in the flux density at high magnetic fields over 300 A/m were mainly dependent on the characteristics of the edge vicinity where the domain pattern was influenced by shearing.     

Effect of deformation and annealing on the microstructure and magnetic properties of grain-oriented electrical steels

The effect of plastic deformation and subsequent annealing on the magnetic properties and microstructure of a grain-oriented (GO) electrical steel has been studied. True strain (ε) from 0.002 to 0.23 was applied by rolling in two directions, rolling (RD) and transverse (TD). The deterioration of power losses varies according to the direction of deformation. Annealing the strained material—at 800 °C/2 h—leads to a recrystallization and restored magnetic properties. The main components of annealed-textures are around 15–35° from those of deformed-textures for both RD and TD. Rolling along {1 1 0} 〈0 0 1〉 direction leads to the development of deformation twins.     

Multilayered perceptron neural networks to compute energy losses in magnetic cores

This paper presents a new approach based on multilayered perceptrons (MLPs) to compute the specific energy losses of toroidal wound cores built from 3% SiFe 0.27 mm thick M4, 0.1  and 0.08 mm thin gauge electrical steel strips. The MLP has been trained by a back-propagation and extended delta-bar-delta learning algorithm. The results obtained by using the MLP model were compared with a commonly used conventional method. The comparison has shown that the proposed model improved loss estimation with respect to the conventional method.     

Surface modification of TiAl alloy via current heating technique

Surface of Ti-52 at% Al alloy was modified via current heating technique. The Ti-52 at% Al alloy with 20 mm diameter × 1.5 mm thick disks was placed in graphitic powder in a glass tube and pressed against it. During the coating process, the direct current was applied across the samples at electrical power of 100-200 W for 10 min. By using X-ray diffraction (XRD), TiC was detected on the alloy treated at 180 W and above. Scanning electron microscopy (SEM) micrographs show the different morphologies, after treatment under different conditions. Energy dispersive X-ray spectroscopy (EDS), SEM and hardness tester show that the carbon concentration, particle size, void size and the hardness of the alloy were increased with the increasing of the applying electrical power, due to the formation of the carbide on the alloy surface.     

Effect of stress relief annealing temperature and atmosphere on the magnetic properties of silicon steel

Fully processed non-oriented silicon steel samples 0.50 mm thick were sheared and submitted to stress relief annealing under different conditions of temperature and atmosphere to investigate the effect of this treatment on the recovery of magnetic properties. Two different compositions were used, with different Si and Al contents. Temperature was varied in the range of 600–900 °C and four atmospheres were used: N₂ and N₂+10%H₂ combined with dew points of −10 and 15 °C. The results showed that annealing atmosphere has very important effect on the magnetic properties and that the beneficial effect of stress relief annealing can be overcome by the detrimental effect of the atmosphere under certain conditions, due to oxidation and nitration.     

Electrical and mechanical properties of graphene oxide on flexible substrate

Graphene oxide (GO) was deposited via the electrophoretic deposition (EPD) method to lower the oxygen concentration of graphene sheets for large-scale production. In addition, the direct synthesis of large-scale GO films using transfer processes on a polydimethylsiloxane (PDMS) substrate was conducted. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties. The Young's modulus values of films with thicknesses of 100–200 nm were 324–529 GPa. Moreover, the GO films exhibited excellent conductivity, with a sheet resistance of 276–2024 Ω/sq at 23–77% transparency. Experiments show that transfer processes for flexible substrates can produce high-quality cost-effective transparent conductive films.     

Sensitivity analysis for estimation of power losses in magnetic cores using neural network

Experimental data from a sample of 42 cores made from grain oriented 0.27 mm thick 3% SiFe electrical steel with dimensions ranging from 35 to 160 mm outer diameter, 25-100 mm inner diameter and 10-70 mm strip width and a flux density range 0.2-1.7 T have been obtained at 50 Hz and used as training data to a feed forward neural network. An analytical equation for prediction of power loss as depends on input parameters from the results of sensitivity analysis has been obtained. The calculated power losses with the analytical expression have also been compared with power loss obtained from the Preisach model after it has been applied to toroidal cores. The results show the proposed model can be used for estimation of power losses in the toroidal cores.     

Effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites

This paper investigates the effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites at operating frequencies between 0.1 and 10 kHz. The magnetic and electrical properties of samples were measured by an LCR meter and morphology of the samples was characterized by scanning electron microscopy. It was shown that the compacted sample prepared at 800 MPa and 550 °C had the lowest magnetic loss and electrical resistivity, and highest magnetic induction and effective permeability in comparison with other samples compacted at 800 MPa and room temperature, 150, 250, 350 and 450 °C.     

Deposition and characterization of TiAlSiN nanocomposite coatings prepared by reactive pulsed direct current unbalanced magnetron sputtering

This work reports the performance of high speed steel drill bits coated with TiAlSiN nanocomposite coating at different Si contents (5.5-8.1 at.%) prepared using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. The surface morphology of the as-deposited coatings was characterized using field emission scanning electron microscopy. The crystallographic structure, chemical composition and bonding structure were evaluated using X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, respectively. The corrosion behavior, mechanical properties and thermal stability of TiAlSiN nanocomposite coatings were also studied using potentiodynamic polarization, nanoindentation and Raman spectroscopy, respectively. The TiAlSiN coating thickness was approximately 2.5-2.9 μm. These coatings exhibited a maximum hardness of 38 GPa at a silicon content of approximately 6.9 at.% and were stable in air up to 850 °C. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions by drilling a 12 mm thick 304 stainless steel plate. Under dry conditions the uncoated drill bits failed after drilling 50 holes, whereas, TiAlSiN coated drill bits (Si = 5.5 at.%) drilled 714 holes before failure. Results indicated that for TiAlSiN coated drill bits the tool life increased by a factor of more than 14.     

Kinetics of electrochemical boriding of low carbon steel

In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm² in a borax based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5-120 min. After boriding, the presence of both FeB and Fe₂B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 ± 200) HV), while the hardness of un-borided steel samples was approximately (200 ± 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 ± 8.6) kJ/mol.     

Influence of target substrate distance on the properties of transparent conductive Si doped ZnO thin films

Si doped zinc oxide (SZO, Si3%) thin films are grown at room temperature on glass substrates under argon atmosphere, using direct current magnetron sputtering. The influence of the target substrate distances on structure, morphology, optical and electrical properties of SZO thin films is investigated. Experimental results show that the target substrate distances have a significance impact on the growth rate, crystal quality and electrical properties of the films, and have little impact on the optical properties of the films. SZO thin film samples grown on glasses are polycrystalline with a hexagonal wurtzite structure and have a preferred orientation along the c-axis perpendicular to the substrate. When the target substrate distance decreases from 76 to 60 mm, the degree of crystallization of the films increased, the grain size increases, and the resistivity of films decreases. However, when the distance continuously decreases from 60 to 44 mm, the degree of crystallization of the films decreased, the grain size decreases, and the resistivity of the films increases. SZO(3%) thin films deposited at a target substrate distance of 60 mm show the lowest resistivity of 5.53 × 10⁻⁴ Ω cm, a high average transmission of 94.47% in the visible range, and maximum band gap of 3.45 eV under 5 Pa of argon at sputtering power of 75 W for sputtering time of 20 min.     

Tribological changes on SS304 stainless steel induced by nitrogen plasma immersion ion implantation with and without auxiliary heating

In order to achieve quite thick treated layers with reasonable thickness uniformity in SS304 steel, the plasma immersion ion implantation (PIII) process was run in high-temperature, up to 350 °C, to induce high thermal diffusion but avoid the white layer formation. In these experiments, we heated the sample-holder with a shielded resistive wire properly wound around it and subjected the SS samples to nitrogen glow discharge PIII with relatively low voltages (10 kV) in different temperatures. We also treated the SS samples by the traditional PIII method, slowly increasing the high voltage pulse intensities, until 14 kV at the end of processing, reaching temperatures of up to 350 °C. These modes of treatments were compared with respect to nitrogen implantation profiles, X-ray diffraction, tribology and mechanical properties. X-ray diffraction results indicated a much higher efficiency of auxiliary heated PIII mode compared to the ordinary PIII. Very prominent γ_N peaks were observed for the first mode, indicating large concentration of nitrogen in thick layers, confirmed by the nitrogen profiles measured by GDOS and AES. Improved mechanical and tribological properties were obtained for SS304 samples treated by the PIII with auxiliary heating, more than for ordinary PIII. Hardness was enhanced by up to 2.77 times, as seen by nanoindentation tests.     

Corrosion behavior of boride layers evaluated by the EIS technique

The corrosion behavior of boride layers at the AISI 304 steel surface is evaluated in the present study. Electrochemical impedance spectroscopy (EIS) technique was used for the evaluation of the polarization resistance at the steel surface, with the aid of AUTOLAB potentiostat. Samples were treated with boron paste thickness of 4 and 5 mm, in the range of temperatures 1123 ≤ T ≤ 1273 K and exposed time of 4 and 6 h. The electrochemical technique employed 10 mV AC with a frequency scan range from 8 kHz to 3 mHz in deaerated 0.1 M NaCl solution. Nyquist diagrams show that the highest values of corrosion resistance are present in the samples borided at the temperature of 1273 K, with treatment time of 4 h and 4 mm of boron paste thickness. The values of corrosion resistance on borided steels are compared with the porosity exhibited in the layers.     

Influence of filler alignment in the mechanical and electrical properties of carbon nanotubes/epoxy nanocomposites

In this work, we report the mechanical and electrical properties of carbon nanotubes/epoxy composites prepared with aligned and randomly oriented nanotubes as filler. The samples are disks of 30 mm in diameter and 3 mm in thickness. To obtain the carbon nanotubes alignment, an external electric field (250 VAC; 50 Hz) was applied through the thickness of the sample during all the cure process. The AC electrical current was measured, during the cure, as a strategy to determine the optimum time in which the alignment reaches the maximum value. DC conductivity measured after the cure shows a percolation threshold in the filler content one order of magnitude smaller for composites with aligned nanotubes than for composites with randomly oriented filler (from 0.06 to 0.5 wt%). In the percolation threshold, the achieved conductivity was 1.4×10⁻⁵ Sm⁻¹. In both cases, aligned and randomly distributed carbon nanotube composites, the wear resistance increases with the addition of the filler while the Rockwell hardness decreases independently of the nanotubes alignment.     

Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0)Si and quartz substrates that were heated at temperatures from 300 to 500 °C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture.     

ZnO/Ag/ZnO multilayer films for the application of a very low resistance transparent electrode

Transparent conductive ZnO/Ag/ZnO multilayer electrodes having much lower electrical resistance than the widely used transparent electrodes were prepared by simultaneous RF magnetron sputtering of ZnO and DC magnetron sputtering of Ag. An Ag film with different thickness was used as intermediate metallic layers. The optimum thickness of Ag thin films was determined to be 6 nm for high optical transmittance and good electrical conductivity. With about 20-25 nm thick ZnO films, the multilayer showed high optical transmittance in the visible range of the spectrum and had color neutrality. The electrical and optical properties of the multilayers were changed mainly by Ag film properties. A high quality transparent electrode, having sheet resistance as low as 3 ohm/sq and high transmittance of 90% at 580 nm, was obtained and could be reproduced by controlling the preparation parameter properly. The above property is suitable as transparent electrode for dye sensitized solar cells (DSSC).     

Magnetic properties and power losses in Fe–Co-based bulk metallic glasses

Magnetic properties of Fe–Co-based bulk metallic glasses have been experimentally investigated. Samples were prepared by water-cooled Cu-mold injection casting technique. The samples have cylindrical shapes with 0.8 mm diameter and 30 mm length. Amorphous structures were confirmed by the presence of a main halo in X-ray diffraction patterns and by the detection of crystallization signal around 650 °C using differential scanning calorimetry.     

Effects of sulfur content and slab reheating temperature on the magnetic properties of fully processed nonoriented electrical steels

The effects of sulfur content and slab reheating temperature on the magnetic properties of four fully processed nonoriented electrical steels have been investigated. Four slabs of nonoriented electrical steels with sulfur content in the range of 0.0006–0.0126 wt% were reheated to 1100, 1200, and 1300 °C, respectively. Then, they were hot rolled and annealed at 700 °C, cold rolled at the same condition and annealed at 820 °C in the salt bath furnace for 1 min to simulate continuous annealing. The ac core loss, dc hysteresis loss, and ac and dc permeability were measured at 15 kG inductions. It was found that the amount of inclusions in the hot-rolled bands increased with increasing slab reheating temperature and increasing sulfur content in steels. After final annealing, grain sizes of cold-rolled steel sheets decreased with increasing sulfur content and increasing slab reheating temperature. The main preferred orientations in the final annealed steel sheets were (0 1 1) 〈1 0 0〉 and (1 1 1) 〈u v w〉 γ fiber texture. Steel sheets containing 0.0032 and 0.0060 wt% sulfur developed a more stronger (0 1 1)〈1 0 0〉 texture than other steel sheets. However, steel sheets containing 0.0126 wt% sulfur had the weakest (1 1 1)〈u v w〉 texture during slab reheating at temperatures higher than 1200 °C. Both ac core loss and dc hysteresis loss increased with increasing slab reheating temperature and increasing sulfur content in steel sheets. Both ac and dc permeability decreased with increasing slab reheating temperature and increasing sulfur content in steel sheets. If sulfur content decreased from 0.0060 to 0.0032 wt%, there were great improvements in ac core loss, dc hysteresis loss, and ac and dc permeability. However, eddy current loss was almost independent of the sulfur content and slab reheating temperature.     

Effects of the sputtering time of ZnO buffer layer on the quality of GaN thin films

ZnO thin films with different thickness (the sputtering time of ZnO buffer layers was 10 min, 15 min, 20 min, and 25 min, respectively) were first prepared on Si substrates using radio frequency magnetron sputtering system and then the samples were annealed at 900 °C in oxygen ambient. Subsequently, a GaN epilayer about 500 nm thick was deposited on ZnO buffer layer. The GaN/ZnO films were annealed in NH₃ ambient at 950 °C. X-ray diffraction (XRD), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of GaN films. The results show that their properties are investigated particularly as a function of the sputtering time of ZnO layers. For the better growth of GaN films, the optimal sputtering time is 15 min.