نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 54 (پاییز 1399)

In the present research, wear behavior of Cr2O3-20YSZ (CZ) and Cr2O3 (C) coatings created using atmospheric plasma spray (APS) process was evaluated. For this purpose, Cr2O3 and YSZ nanopowders were produced after milling for 5h in a high-energy ball mill and subsequently plasma spraying of the agglomerated powders was carried out on 304L substrates. Microstructural characterization of these ceramic coatings was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and optical microscope. Mechanical tests including adhesive strength, fracture toughness, and micro-hardness were used so as to explain the coatings wear behavior. Sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of YSZ particles to the Cr2O3 matrix due to the phase transformation toughening mechanism associated with tetragonal zirconia resulted in an increase in the fracture toughness while decreased the micro-hardness. It was found that the composite coatings had the friction coefficients of the proper order of 0.11-0.15. The CZ composite coating compared to the C coating showed the higher wear resistance so that the weight loss was obtained as 11 and 31 mg, respectively. Observation of the wear tracks of the coatings indicated that the lower wear rate of the CZ coating was attributed to its higher toughness and therefore filling the pores due to the higher plastic deformation of its wear debris.

In this study effect of microstructure and crystallographic texture on the hydrogen induced cracking resistance of a HSLA was investigated. Samples were hot rolled between 980 to 750 °C up to 50% and quenched in different environments. Microstructure and texture of the samples were studied using a scanning electron microscope (SEM) equipped by electron backscattered diffraction detector (EBSD). Hydrogen induced cracking resistance of the samples were also evaluated using HIC test. Results revealed that, by increasing cooling rate more non-equilibrium phases with finer grain where formed. Grain boundary fraction also increased by increasing cooling rate which led to decrease in HIC resistance. Texture of the samples were also changed due to cooling rate enhancement furthermore texture intensity decreased. {111} // ND fiber intensity decreased due to cooling rate increase which led to decrease in intergranular crack propagation and consequently decrease in HIC resistance.

In order to improve the surface properties and the greater use of aluminum and its alloys in various industries, especially aerospace, different coating methods have been introduced. Anodizing and electroless plating are the most widely used methods for this purpose. In this research, the effect of temperature and voltage of anodizing on the surface properties of anodic aluminum oxid (AAO), producred on 2024 aluminum, was investigated. The results showed that with increasing voltage and decreasing temperature, the thickness and roughness of coatings increased. An optimal voltage (45 V) was obtained to achieve the highest hardness at all temperatures. The study of the thickness and hardness of the optimum sample also showed an increase in these two parameters with increasing time. FESEM studies also revealed that by carefully controlling on the anodizing conditions, a structure with regular nano-cells could be obtained. The two step anodizing significantly increased the order of the oxide layer cells. SEM, EDS, and XRD results indicated that the possibility of Ni-P electroless coating applying on anodized aluminum in SLOTONIP 70A solution is well established. To investigate and compare the corrosion behavior of AAO and AAO/Ni-P coatings with aluminum substrate, the polarization method and tafel extrapolation was used. The results indicated that the high corrosion resistance of 2024 aluminum alloy was achieved in the presence of Ni-P electroless coating on anodized alloy. The heat treatment of the samples at different temperatures showed that the highest hardness of the final coating (1185 vickers) would be achieved at 400 °C, and the heat treatment time at this temperature after 75 minutes would not have much effect on the hardness.

In this study were examined the effect of adding zinc cation instead nickel cation on the structural and magnetic properties of nickel ferrite prepared by sol-gel method. X-ray diffraction, field emission scanning electron microscopy, energy resolution spectroscopy, Fourier transform infrared spectroscopy, vibrating sample Magnetometer and vector analysis network device produced were used to verify the structural characteristics and magnetic ferrite particles. Single temperature recognized for nickel ferrite doped with zinc ions, 1200oC.For samples the doped ferrite phase and the second phase was achieved without any impurities. Scanning electron microscopy images showed obtained by particle size increases with increasing substitution of cation zinc. Breakdown spectroscopy graphs showed substituted increase energy and reduce peak of cation zinc peak size by increasing the nickel of cation. Fourier transform infrared charts compounds to confirm the results of X-ray diffraction patterns indicate the phase formation and placement of metal cations in spinel structure. Magnetic hysteresis curves, respectively increasing the saturation magnetization and the residual magnetization to combine x=0.6 and then reduce them to combine x=1. Waste dehydrogenation magnetic have consistently decreasing trend until combined x=0.8 and then will combined x=1. With zinc substitution increased reflection loss. Zinc cation by nickel ones, causes improving of the magnetic properties and microwave absorbtion and this material could be used for the different applications such as microwave absorbance.

In this study, NiFe2O4-CdO compound nanoparticles were prepared through co-precipitation. The two variables of the synthesis method are, respectively, the temperature gradient reaching the temperature of the heat treatment of 500 ° C at 10°C/sec, 35°C/sec and 60 °C/sec and the pure oxygen pressure as the heat treatment atmosphere for 0.5 hours, at 0.5 psi, 1 psi, and 1.5 psi. So, we found 9 samples, that the sample with the best sensitivity response to formaldehyde was characterized. X-ray diffraction, scanning electron microscopy, transition electron microscopy and X-ray fluorescence experiments were used to study the structure of these nanoparticles. X-ray diffraction experiment is confirmed formation of nickel ferrite and cadmium oxide phases. Scanning electron microscopy and transition electron microscopy experiments are confirmed nickel ferrite and cadmium oxide being nano-structure. NiFe2O4-CdO formula ratio is confirmed by X-ray fluorescence experiment. The sensitivity property of NiFe2O4-CdO nanoparticles for formaldehyde gas detection was studied at 50 °C. For testing the sensitivity of nanosensors, we used a laboratory 5 liters system with temperature and humidity control. This system equipped with a temperature control heater for heating sensors. Relationship between gas concentration (from 10 ppm to 200 ppm) and resistance change of nano sensor with the best response to formaldehyde was investigated, that this relationship was found linear.

In this research, the effect of different substitution quantities of zinc cations on electromagnetic and microwave absorption properties of Z-type barium hexaferrite with chemical composition of Ba3Co2-xZnxFe24O41 (x=0, 1.2, 1.3, 1.4, 1.5, 2) generated by high energy milling method was studied. X-ray diffraction (XRD) method was used to verify the formation of Z type Ba-hexaferrite phase in the synthesis conditions. Magnetization properties of different compositions were studied by alternative gradient force magnetometery (AGFM). X-ray diffraction (XRD) method was used to confirm the formation of Z-type Ba-hexaferrite phase. The investigations by AGFM showed that the amount of magnetization increased by substituting the desired composition. So that the amount of magnetization (67 emu/g) for an unsubstituted sample will reach its maximum (84 emu/g) for the sample with composition of . In addition, complex permeability and permittivity coefficients of the samples were studied by vector network analyzer (VNA). Using the measured coefficients, reflection loss curves were plotted. The results of the reflection loss (RL) plots showed that, on average, the maximum absorption bandwidth occurred among the samples at a frequency range of 4-8 GHz. The best absorption (the most negative reflectance loss) was observed at -47 dB and at a frequency of 7 GHz for the sample with an index of substitution of x=1.3.

Synthesis of metal oxide nanoparticles using microorganisms and plants, so-called green synthesis methods, has received a great amount of attention because of its easy and inexpensive synthesis condition with respect to usual chemical and physical methods. The luminol chemiluminescent reaction is among well-known quantitative methods in analytical spectroscopy due to its high sensitivity to presence of catalyst and low background signal. In this study, Fe3O4/SiO2/ZnMn2O4 nanocomposite was prepared by the green method using Aloe Vera extract solution and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and vibrating sample magnetometer (VSM). These magnetic nanoparticles were used as a catalyst in the luminol-H2O2 chemiluminescence system. The obtained results indicated that these nanoparticles have good catalytic activity in the chemiluminescence system so that the emission intensity was increased about fourfold in presence of catalyst at 3 second. The recovery of this catalyst was easily performed by an applying external magnetic field.