نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 62 (پاییز 1401)

In this research, the effect of input parameters of Electrical Discharge Machining (EDM) on A356 nano-composite reinforced by 3.5% alumina (Al2O3) was examined and optimized by the Taguchi technique based on the L9 orthogonal array and duplicated levels technique. The input parameters of these experiments consisted of voltage (two-level), current intensity (three-level), pulse on-time (three-level), and pulse off-time (three-level). Moreover, the output parameters were comprised of the material removal rate of the workpiece, the tool wear rate of the machining, and the surface roughness of the workpiece. The analysis of the results and investigation of the signal-to-noise graphs (S/N) and variance analysis (ANOVA) were carried out by using software. Also, with the determination of the loss function of total normalized values of the output parameters based on appropriate weight coefficients, the optimum level of each input parameter was identified. Besides, with performing the variance analysis, the magnitude of contribution percentage of each of the input parameters in the total variance was calculated. Based on the obtained results, it was concluded that the most influential parameter on the material removal rate was the pulse off-time, on tool wear rate was the current intensity, and on the surface roughness was the pulse on-time. Furthermore, the first level of the voltage (80 V), the first level of the current intensity (10 A), the first level of the pulse on-time (35 µs), and the second level of the pulse off-time (70 µs) were determined as the optimum input parameters. The contribution percentage of the input parameters in the total variance for voltage, current intensity, pulse on-time, and pulse off-time was found to be 12.98, 20.96, 5.47, and 60.60, respectively.

Solution precursor thermal Spraying (SPTS) processes are suitable methods for producing nano-structured coatings. Due to the uncompleted reactions such as solvent evaporation and pyrolysis of the precursor, achieving coatings with controlled properties at a satisfactory precipitation rate remains an important challenge in these processes that needs to precise control of spray parameters. In this study, in order to investigate the effect of Solution precursor high velocity flame spraying parameters such as fuel and oxygen content, spraying distance and solution injection rate, single-scan spraying test was performed on glass substrates. The morphology of the formed splats and their structural characteristics were investigated using Scanning Electron Microscope (SEM). Structural comparison in the single-scan spraying test performed in two ratios of fuel to oxygen, showed that in the flame parameter with oxygen pressure of 6 bar and fuel 3 bar at the injection rate of Solution precursor 20 cm3/min and spray distance of 5 cm was selected as the optimal parameter. In this parameter, due to the low injection rate of the solution and higher heat transfer per drop of the solution precursor and completion of processes that resulting in melting and crystallization, the number of splats increased. Also, evaluation of single-scan spraying in the flame with oxygen pressure of 8 bar and fuel bar of 4 bar and spray distance of 5 cm showed that the injection rate of 40 cm3/min solution precursor would be more appropriate due to increasing the number of fine splats and improving coating efficiency.

In this study, the effect of adding graphene oxide on the terbiological behavior of coatings created by the electrolytic plasma oxidation process under constant voltage conditions has been investigated. Bipolar waveform coating operation was performed on the surface of AZ31 magnesium alloy for 10 minutes. The results showed that the surface morphology of the coatings had micro-cavities known as pancake structure and volcanic crater on the surface, the diameter of which increased with the addition of graphene oxide. Fuzzy analysis of coatings showed that the coatings are composed of oxide phases of forsterite and periclase. The wear mechanism of the coated samples was scratched. Also, the wear resistance of the coating containing graphene oxide additive increased so that the average coefficient of friction for the mentioned samples decreased 10 times compared to the uncoated sample, which is due to the increase in hardness. The hardness of the sample containing graphene oxide has increased about 5 times compared to the magnesium alloy. Magnesium alloy with this coating is a good candidate for orthopedic applications.

Metal matrix composites, high mechanical performance, usability at high temperatures, good wear resistance and low creep rate. This type of composite manufacturing method is very important. Among manufacturing processes, ARB process as a method of applying severe plastic deformation is used on the sheets. In this study 5Wt. % Al/alumina composites fabricated by accumulative roll bonding process up to eight steps using Al1060. Microstructure, mechanical properties and corrosion behavior of the composite were studied by scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), measurement in 3.5wt% NaCl solution. Corrosion behavior of the composite revealed a considerable improvement in the main electrochemical parameters, as a result of enhancing influence of cold rolling. Also, the electrochemical experiments showed that corrosion resistance of samples increasing with increasing the number of ARB cycles. After 8- cycle ARB have a low corrosion density in comparison with high corrosion density of annealed specimens.

Metal-organic frameworks (MOFs) have been used as electrode materials in supercapacitors (SCs) due to their high specific surface area and suitable porosity size. However, using single-component MOFs in SCs leads to poor electrical conductivity, insufficient stability, and poor mechanical properties, and thwarts the effect of high capacity and efficient performance. In this paper, to improve the electron transfer rate and take advantage of the specific surface of MOFs, nickel-based metal-organic framework/graphene nanocomposites were prepared by hydrothermal in-situ synthesis, and to prevent agglomeration, graphene (0, 2.5, 5, and 10wt%) was added during the synthesis process. To characterize the structure of the nanocomposites, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) were used. To study the supercapacitor behavior, electrochemical tests, such as cyclic voltammetry, electrochemical impedance, and repeatability behavior were used. The electrode prepared by the nickel-based MOFs in the 6M KOH electrolyte had a specific capacity of 660 F/g, while their composite with graphene had a specific capacity of 1017 F/g. As a result, benefiting from composite properties and increasing electrical conductivity of MOFs with graphene resulted in greater porosity availability and increased total storage capacity.

The effect of gadolonium cation substitution on the structural and electromagnetic properties of Z-type barium hexaferrite was investigated in this study. This group of compounds is known as Ba3Co2-xGdxFe24O41, and it was created using the energetic milling approach with substitution values of 0, 0.1, 0.3, 0.5, 0.8, 0.1, and 1.2. X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM) photos of Ba3Co1.6Gd0.4Fe24O41 samples were obtained to investigate the phase formation temperature and the effect of particle size on the properties of this compound. A network vector analyzer was used to assess the real and imaginary components of the samples' electrical permittivity (ε) and magnetic permeability (μ) in order to evaluate their electromagnetic properties (VNA). Using these coefficients, reflection loss diagrams of the compounds were created in the frequency range of 1-18 GHz. By examining the samples in terms of maximum absorption intensity and bandwidth at the same time, the samples with Gd substitution with x = 0.5 in the frequency bands S and C1, the sample with x = 0.3 in the band C2, the sample with x = 0.3 in the X band, the sample with x = 0.1 in the X band, and the sample with x = 1.2 in the Ku band were chosen as the optimal samples (S: 1-2 GHz, C1: 2-4 GHz, C2: 4-8 GHz, X: 8-12 GHz, Ku: 12-18 GHz).