فصلنامه علوم و مهندسی سطح ایران
پیاپی 47 (بهار 1400)

Coating is one of the processes used to improve the tribological properties of surfaces. In this article, the increase in useful lifetime of soft-coated part and the validity of Miner’s rule for predicting adhesive wear are investigated. In order to achieve this aim, a series of pin-on-disk experiments on three sets of disks were performed by single-force, two consecutive-forces and three-forces loading conditions, at two constant speed levels. These experiments were performed for simple, double-layer and four-layer coated disks. As a result, the validity of Miner’s rule for consecutive loads at a constant speed is shown. Also, the work done by friction force and wasted energy are investigated. It is shown that for each of the parts with a specified coating, regardless of loading sequence, the work done by friction force up to the failure point is almost a constant value.

Friction stir processing (FSP) was performed on a 2024 aluminum alloy sheet with a thickness of 2.5 mm. Determination of the parameters affecting on the microstructure is very important to investigate the grain size changes in Thermo-Mechanically Affected Zone (TMAZ). In this study, were investigated the effect of tool rotation speed on the microstructure and mechanical properties of the areas around the stir zone when keeping the traverse speed constant. The average grain size in advancing side were decreased from 6 μ to 3 μ by increasing rotation speed from 315 to 500 rpm and were increased from 3μ to 7μ by increasing rotation speed from 500 to 800 rpm. The average grain size in retreating side were decreased from 7μ to 4μ by increasing rotation speed from 315 to 500 rpm and were increased from 4μ to 8μ by increasing rotation speed from 500 to 800 rpm. Also the advancing side’s grain size was smaller than that of the retreatin side. The mechanical properties of advancing and retreating sides were semillar.

In this work, diamond-like carbon (DLC) films were deposited on silicon substrate by an ion beam method (IBM ) using propane (C3H8) and argon (Ar) gases. Then, thermal annealing effects (from 200ºC to 500ºC) on the chemical and optical properties of the diamond-like carbon thin films were investigated. Structures, morphology, chemical and optical properties of the films were investigated by Raman spectroscopy, field emission scanning electron microscopy (FESEM ) and fourier transform infrared (FTIR) spectrometry methods. The Raman results proved that increasing of the annealing temperature (Ta) cause to the conversion of chain links to aromatic rings. Based on the FESEM results, the micro-cracks were formed in the film at 200 ºC. Altogether the results showed that decomposition of the DLC films begins at the annealing temperature above 300 °C. As Ta was further increased to 500 °C, the main part of the film was oxidized. Also FTIR analysis indicated that by increasing Ta, the transmission of the DLC film was decreased in the wavelength range of 3-5 μm.

In this study, the plasma etching of a graphene layer (in order to make it porous) deposited on a SiO2 substrate was investigated. Therefore, for the first time, the process of the graphene layer bombardment with the oxygen ions was simulated by molecular dynamics simulation using LAMMPS. Moreover, the effect of the bombarding ion energies on the etching process was studied. Our results showed that with increasing the oxygen ion energies from 3 eV to 12 eV, the number and size of the created holes in the graphene layer increase. Investigation of the radius distribution function of the graphene layer before and after the bombarding process also showed that the etching process has caused some sort of irregularities in the graphene layer. In addition, the average number of C-C bonds in the graphene layer decreased with the oxygen ion energies which is the indicator of the fact that the C-C bonds have been broken with increasing energy. Moreover, the results showed that at the energy of 3 eV for the oxygen ions, the graphene layer remains almost undamaged. It is noteworthy that the Reax force field is used in the simulation which predicts the formation of O2, CO, CO2, C2O2 and CO3 species.