فصلنامه علوم و مهندسی سطح ایران
پیاپی 56 (تابستان 1402)

The optical properties of silicon oxynitride thin films (SiON) have been investigated. SiON films were grown on glass and silicon substrates by plasma enhanced chemical vapor deposition. A radio frequency power source with a capacitor coupler is used to produce plasma. Moreover, tetraethyl-orthosilicate (TEOS), oxygen, and nitrogen have been used as silicon source, oxidizing gas, and nitrogen source, respectively. Growth mechanism and the variation of the refractive index as well as the variation of the optical absorption of the films have been studied. From the results, it can be understood that the atomic and ionic active nitrogen species produced in the plasma volume act similar to oxygen species in the oxidation mechanism and cause the decomposition of TEOS molecules. Therefore, the increase of nitrogen flux in the plasma gas mixture results in the reduction of organic impurities caused by TEOS monomers. The roughness of the films was measured below 0.2 nm. The results also showed that by adding nitrogen gas in the plasma gas mixture, it is possible to increase the refractive index of the silicon oxide films without significant change in their transparency. Finally, with the increase of nitrogen flux from 0 to 80 sccm, the refractive index of the films increased from 1.446 to 1.464, while the optical absorption was measured to be less than 1 in all cases.

In this article, the microstructural characteristics of silicon-aluminide coatings with and without chromium applied on the Rene-80 nickel base superalloy substrate are presented and analyzed. To add chromium to the aluminide coating, enriching the surface layer of the alloy with chromium was carried out in two ways: (1) chrome plating and (2) pack cementation chromizing. Besides, the diffusion annealing of the plated chromium layer was also carried out with the aim of increasing the depth of the chromium-rich layer. SEM, EDS and XRD methods were used to characterize the coatings, including the quantity and quality of the coating layers, microstructural characteristics and elemental and phase composition. Investigations showed that the addition of chromium to the silicon-aluminide coating causes the presence of chromium in the upper part in the form of chromium silicide precipitates. The silicon precipitates in the upper part of the aluminide coatings is in the form of deposits of refractory elements, and the silicide chrome precipitates is formed more than other precipitates. In order to provide resistance to hot corrosion, at least 8% by weight of chromium and 10-13% by weight of silicon are required in the upper layer of the coating. The amount of chromium and silicon elements in the upper part of both CrSiAl-P and CrSiAl-E coatings was relatively similar and in the range of 12-14 and 13-14% by weight, respectively. Of course, the observations indicated that added chromium in both types of coating contributes to the formation of chromium-rich deposits, but more in the lower areas of the coating.

this research focused on investigating the optimization and corrosion studies of rhodium plating coatings. Firstly, a rhodium coating was applied to the Inconel 600 super alloy substrate for 2, 5, 10, 20 and 50 minutes, using the electroplating process of sulfate solution. Using scanning electron microscope (SEM) and X-ray energy spectroscopy (EDS) images, the thickness, morphology and elemental analysis of the surface coatings were investigated and effect of rhodium plating time on the thickness and surface roughness of the coating was investigated. Finally, the corrosion resistance of rhodium coatings in 3.5%wt NaCl solution was evaluated using electrochemical tests: open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and tafel polarization, respectively. The results of SEM and roughness measurement studies in comparison results of rhodium coating showed that the electroplated rhodium coating had the highest resistance to electrochemical corrosion in 10 minutes, the thickness of the coating was 1.27μm and the corrosion current was 6.25nA/cm2 and the corrosion potential was determined to be 193mV vs SCE. the changes in the surface roughness were similar to the results of fitting the simulated electrical equivalent circuit for the double layer capacitance of the electrochemical impedance test.

The purpose of the present research is to investigate the wear between two surfaces of coated spur gears under the mixed lubrication regime by employing the load sharing concept. By considering the coating in the problem and considering its geometric properties and material, the modeling parameters such as the equivalent radius of curvature, the equivalent elasticity modulus, the equivalent roughness and the hardness of the cylinders are changed, which leads to the change of the dimensionless parameters of the problem and as a result the values of friction and wear are calculated. Considering that the contact of the surfaces of two gears in one round of their rotation can be modeled as the contact of a large number of cylinders, the problem of linear contact of cylinders is extended to the contact of the surfaces of two gears in one round of their rotation. to be This modeling is covered by using a desired and appropriate coating such as DLC on the surfaces of the gears. One of the important parameters obtained is the critical coating thickness or minimum coating thickness. Based on the results obtained, if the selected coating thickness is less than the critical thickness, the wear rate does not improve. It was also concluded that the material of the selected coating should also have a suitable hardness in order to reduce the wear rate sufficiently.

One of the most important issues in machining processes is the optimal use of resources, including tools, coolants and time, by achieving optimal parameters. The presence of friction between tools and workpieces during machining has always led to a rise in temperature and a negative impact on machining parameters, especially on tool life.Steel 1045 is one of the most difficult metals to machine in industry, and its machining usually results in damage to the tool and a reduction in tool life and the time required for machining. In addition, its high wear resistance makes it one of the most commonly used metals in various industries. Increasing the tool life is very important when machining this steel. In this study, by changing the cutting and clearance angles of the highspeed steel tool when turning 1045 steel, the effect of the above parameters on the amount of tool wear at cutting speeds of 30 and 40 m/min at two feed rates of 0.05 and 0.2 millimeters per lap was examined. The innovations carried out in this research include the modifications made to the TN50 lathe in Tabriz and the transformation of the machine into a CNC machine, the use of highspeed steel tools in the machining of 1045 steel, and the use of the CNCMCO microscope. The results showed that, on average, the free angle of 9 degrees and the rake angle of 15 degrees reduce the tool wear due to a more suitable wedge angle to maintain the strength of the cutting edge of the tool and a suitable rake angle to remove the crisps from the working surface faster. will In addition, with the increase of the cutting speed and the feed rate, the tool life is reduced due to the increase of the temperature of the cutting edge of the tool, which can be understood by comparing the resulting data.

Prediction of the failure lifetime of thermal barrier coatings (TBCs) is usually considered as one of the important challenges in the hot section components of gas turbines. In this study, the effective stresses in determining the lifetime of new-generation single-layer Gd2Zr2O7 (GdZO) and dual-layer ZrO2-8Y2O3 (YSZ) / GdZO TBCs were investigated. For this purpose, singlelayer GdZO and dual-layer YSZ / GdZO TBCs were applied on IN738LC / CoNiCrAlY by atmospheric plasma spraying technique. Then, their cyclic oxidation behavior was studied at 1100°C with 4-h cycles. The morphologies of the TBCs (before and after oxidation) were investigated by field emission scanning electron microscopy. In addition, the mechanical behavior of the TBCs was examined by the Nanoindentation test. The variation in the energy release rate of the TBCs during oxidation cycles was calculated. The results showed that the changes in the energy release rate of dual-layer YSZ / GdZO TBC compared to single-layer GdZO TBC are less, and, therefore, have a better high-temperature performance. Applying an intermediate YSZ layer between the bond and top coats enhances the mechanical properties of new-generation TBCs and extends their lifetime by improving their resistance to high-temperature oxidation.