IRANIAN JOURNAL OF SURFACE SCIENCE AND ENGINEERING
Year:2020 | Volume:- | Issue:44|Papers Count:5

Metal implants are widely used in medical and dental areas due to their good mechanical properties. The use of these metal implants in the corrosive environment of the body involves many problems, including the problems of corrosion-induced products that cause infection and cause the type of implants in the body to not function properly. In this research, sol-gel method was used to apply the hydroxyapatite / titanium dioxide coating on 316 Stainless Steel Alloy. All samples were coated with optimum conditions at 10 cm / min and pH =7, and then the corrosion resistance of the coatings was investigated in a ringer solution using potentiodynamic polarization and EIS methods. The composition of the coatings is also analyzed by XRD, EDX, FTIR. The morphology of the coating is determined by the scanning electron microscope (SEM). The results of the study showed that HA and TiO2 coatings and HA / TiO2 nanocomposite with 75, 50, 25% TiO2 coatings on a uniform thickness of 316 steel substrate. The results of the FESEM images showed that hydroxyapatite and titanium dioxide on the steel alloy 316 has uniform coverage and denser, and also by increasing the percentage of titanium dioxide nano hydroxyapatite / titanium dioxide from% 25 to% 50 It then becomes 75% nano-particles smaller and the coating becomes dense. Corrosion tests showed that the corrosion resistance of 316 Stainless Steel Alloy coated with nano HA / TiO2 by increasing the amount of TiO2 in the coating increases.

The purpose of this research is to improve the quality and efficiency of Yttria-stabilised zirconia (YSZ) thermal barrier coating (TBC) in Na2SO4-V2O5 environments through the addition of NiTi powder. For this purpose, YSZ coatings with and without 5 Wt. % NiTi powder were deposited by atmospheric plasma spray (APS) technique on a Ni-based superalloy (IN738LC) substrate as a top coat with a CoNiCrAlY bond coat. The hot corrosion resistance of the samples was investigated in a furnace by cyclic mode in Na2SO4-55 wt. % V2O5 salts. Each cycle consists of 4 h heating at 950° C. The results indicated that the molten salts at the working temperature can react with Yttria, the stabilizing compound of YSZ, and cause the transformation of tetragonal zirconia to monoclinic phase during cooling. This transformation results in a volumetric expansion which can lead to cracking and spallation of the surface layers of the thermal barrier coatings. Microstructural and phase studies of coatings before and after hot corrosion tests confirmed the better hot corrosion resistance of YSZ-5Wt. %NiTi composite coating compared to YSZ due to delay in crack propagation and the tetragonal phase transformation to the monoclinic.

In this study, the graphitic amorphous carbon (g-C) thin films were deposited by the ion beam sputtering deposition (IBSD) technique on glass substrates. The effect of ion beam energy on the optical and structural properties of thin films was investigated in the wide range from 1. 8 keV to 5 keV. The results of investigation about optical and structural properties using UV-visible spectroscopy and Raman spectroscopy respectively showed a direct correlation between structural and physical developments. Raman spectra indicated a structural transition from graphite to nano-crystalline graphite phase. The values of ID/IG ratio, optical transparency and optical band gap depend on the ion beam energy; all of them increased by increasing argon ion beam energy from 3 keV, which is associated with a decrease in the film thickness. Furthermore, the sheet resistance of the samples was measured by the four-point probe (FPP) followed similar trends of these structural properties. According to Tauc equation the maximum optical band gap was equal to 3. 75 eV by the graphite crystallites (with sp2 bands (La)) equal to 5 nm in amorphous carbon thin film deposited with the highest argon ion beam energy of 5 keV.

In this research, effect of surface characteristics including restitution coefficient, cohesion factor, sliding friction and rolling resistance on the green pellet motion on the roller screen were studied numerically with the aid of discrete element method (DEM). Sensitivity analysis pertaining to integration time step and surface meshing were conducted to ensure the results accuracy. Curve fitting were applied on the numerical results to represent the critical speed versus the surface characteristics in mathematical functions. Based on the obtained results, the critical speed was increased by increasing the sliding friction however, when this coefficient exceeds a limit (around 0. 3) its impact became negligible. Moreover, it was revealed that by increasing the rolling resistance, the critical speed was reduced. Regarding the restitution coefficient, it was observed that increasing this factor increases the possibility of remaining the pellet between the rollers. Furthermore, it was concluded that cohesion can cause increasing or decreasing of the critical speed depending on the other surface characteristics.