فصلنامه علوم و مهندسی سطح ایران
پیاپی 58 (زمستان 1402)

In this research, super-hydrophobic surfaces were made on pure aluminum (92%) using two methods of chemical etching, and onestep anodizing and modification with materials with low surface energy. After creating a uniform roughness on the surfaces, surface modification was done with perfluoroactyltrichlorosilane (PFTS). The wettability was investigated by measuring the drop contact angle (WCA) and the morphology of the coating with a field emission scanning electron microscope (FESEM). The chemical composition of the surface was detected by Fourier transform infrared spectroscopy (ATR-FTIR). The self-cleaning property with coal powder was investigated. Corrosion behavior was evaluated using Tafel polarization test and salt fog. The results of the water contact angle showed that the surface roughness due to anodizing and chemical etching reduced the contact angle to 15ᵒ and 24ᵒ, and after modifying the surfaces, the contact angle increased to 157ᵒ and 153ᵒ. After modifying the surface of the anodized sample, it has higher corrosion resistance than the etched sample. The final coating is self-cleaning.

Mechanical moving assemblies and direct contact between surfaces in vacuum used in space applications have led to extensive research to find solid-solid lubricant coatings with high wear resistance, including Diamond-Like Carbon (DLC) coatings. Depending on the properties required, different methods of deposition were used for diamond like carbon (DLC) coating. In this research, the DLC coating was synthesized by electroplating method at high voltages on copper substrate. The types of carbon and coating bonds obtained were studied by Raman spectroscopy. The tribological and microstructural properties of the samples were studied by means of microhardness analysis, wear test, and FESEM. An acceptable amount of sp3 bands was obtained in the coating of DLC by electro plating method at a voltage of 470 volts. Examination of FESEM images revealed that a structure similar to cauliflower. The hardness of electroplated coatings is high due to the high amount of sp3 bands, the hardness value was measured around 1600 Vickers. The coefficient of friction of DLC coating is low and acceptable in short distances, which is suitable for space hinges with low range of motion, but with the increase of the distance, it increased significantly.

In this research, the effect of nitrogen ion radiation on the surface properties and structure of titanium metal was investigated. For this purpose, titanium samples were subjected to 2.7 kJ focal plasma device with nitrogen ions emitted from it in 5, 10 and 20 shots of the plasma device. The focus was irradiated. SEM, EDX and XRD analyzes were taken from titanium samples before and after irradiation. The results of SEM show that with the irradiation of ions on the surface of titanium, rough blisters are created on the surface of the specimens; the density and size of these blisters increase with the number of shots. Also, on the surface of the irradiated samples, sputtered areas were observed, owing to the increase in the temperature of the titanium surface by the impact of high-energy nitrogen ions. The X-ray diffraction results showed that with the irradiation of nitrogen ions onto titanium, the diffraction pattern has undergone changes in the peak locations; the peaks shifted to smaller angles, due to the stress and strains created in the surface layers as a result of high heat transfer to titanium during the irradiation of nitrogen ions. In addition, the irradiation of nitrogen ions on titanium caused a decrease in the height of the peaks. The results obtained from EDX also revealed that by irradiating nitrogen ions on the titanium, a small amount of copper has been deposited on the titanium surface due to evaporation from the anode head of the focal plasma device.

NiCoCrAlY coatings are applied through thermal spraying and physical vapor deposition (PVD) methods. The utilization of the PVD technique offers superior properties attributed to reduced porosities and impurities within the coating. In this study, NiCoCrAlY coating was applied on Mar-M-200 nickel-base superalloy using cathodic arc evaporation physical vapor deposition (Arc-PVD). Coatings were produced at bias voltages of -180 and -240 volts, along with arc currents of 80 and 110 amperes. Investigating the effects of negative substrate bias voltage and arc current on the microstructure, defect density, morphology, and phase transformation of the coatings was conducted using an optical microscope (OM) and scanning electron microscope (SEM) equipped with EDS analysis. The experimental findings indicated that increasing the arc current from 80 A to 110 A increased the coating thickness, whereas the thickness decreased at the higher bias voltages. The A110B180 sample exhibited a maximum coating thickness of 13.5 microns. Furthermore, an increase in the arc current resulted in the enlargement and increased number of macroparticles, reaching up to 50 microns. X-ray diffraction analysis of the coatings also demonstrated that the main phases of the coating included γ΄-Ni3Al, γ-Ni, and α-Co, and with increasing arc current from 80 A to 110 A, the intensity of γ΄-Ni3Al and γ-Ni peaks increased. By increasing the bias voltage from -180 V to -240 V, the crystallite sizes were enlarged. Conversely, elevating the arc current from 80 A to 110 A led to a reduction in crystallite size. In the A110B180 and A80B240 specimens, the smallest and largest crystallite sizes were measured at 18 and 24.2 microns, respectively. A comparative analysis of the coated samples revealed that the A110B240 coating exhibited a lower defect density and relatively greater thickness, so it can propose more favorable properties for industrial applications at elevated temperatures such as the hot section blade of the gas turbine.

The effects of 0.7-3 ppm thiourea on the structure and corrosion properties of electroless nickel-phosphorus coatings were evaluated. SEM, AFM and EDS analyses were used to investigate the morphology, topography of the coatings and their elemental composition, respectively. A micro hardness test was performed to evaluate the hardness of the coatings. The corrosion behavior of the coatings was evaluated in in 3.5 wt.% NaCl aqueous solution using Tafel polarization test and electrochemical impedance spectroscopy method. It was observed that at 0.7 ppm concentration of thiourea, the solution was decomposed after 10 minutes, but electroless solution containing 1-3 ppm thiourea was stable during the deposition for one hour. The solution containing 1 ppm had the highest coating speed (10.21 m/hµ), which was decreased with increase of thiourea concentration to 3 ppm (2.5 m/hµ). In addition, by increasing the concentration of thiourea from 1 ppm to 3 ppm, the amount of phosphorus was decreased from 12.64 to 2.4 wt.%, which caused a change in the crystallographic structure from amorphous to crystalline and a decrease in hardness from 610 ± 15 Vickers to 198 ± 20 Vickers. By increasing the amount of thiourea in the electroless bath from 1 ppm to 3 ppm, the corrosion resistance was decreased so that the corrosion current density was increased from 6.91 × 10-7 A.cm-2 to 4.07 × 10-6 A.cm-2 and the charge transfer resistance for nickel-phosphorus electroless coatings was decreased from 3151 Ω.cm2 to 625.3 Ω.cm2 . The obtained results can be due to the absorption of thiourea on the surface of the substrate or nickel-phosphorus coating and preventing the continuation of the electroless process.