فصلنامه علوم و مهندسی سطح ایران
پیاپی 39 (بهار 1398)

The aim of this study was evaluated the chemical resistance of diamond like carbon deposited on polycarbonate substrate. For this purpose, plasma etching treatment using argon and oxygen gases at various times were applied on the surface of polycarbonate substrates. Then the effect of O2 and Ar plasma pretreatment on wettability and surface chemical bonding of the polymers were investigated by water contact angle analyzer and Fourier transform infrared spectroscopy methods, respectively. Diamond-like carbon (DLC) thin film was deposited on the etched polymers by Radio Frequency- Plasma Enhanced Chemical Vapor Deposition (RF- PECVD) method using gas mixture of CH4 and Ar. The adhesion of the DLC films was investigated by tape test. Chemical stability of the coating was evaluated by exposing the samples under to acetone and sodium hydroxide solutions. The results showed that plasma etching with O2, because of formation of hydroxyl group and consequently more reduce in contact angle, were the most effective pretreatment method for improving the adhesion of the DLC film on the polymer surfaces. Study of the raman spectra peak intensities indicated that deposition of the DLC thin film improved chemical resistance of polycarbonate substrate after the exposing to acetone and sodium hydroxide solution.

Electroplated nickel composite coatings have good wear resistance. In this study, by adding Ag particles as reinforcement and optimization of electroplating conditions, wear behavior, hardness and roughness of Ni-Ag have been studied. Taguchi design of experiment (DOE) technique was carried out for optimizing four effective parameters (Ag content, current density, time and additives) and three levels. Therefore, nine specimens were prepared and morphology and structure of the samples were analyzed by SEM and X-ray diffraction. To find out the wear resistance of the samples, pin–on–disk test was performed and worn surfaces were analyzed by SEM and EDS. The optimized parameters of electroplating, based on signal to noise ratio (SNR) curves, were 50 mg/L Ag content, 4A/dm2, 2 hours electroplating and Triton X100 as additive in order to achieve the lowest wear. Analysis of variance (ANOVA) calculation showed current density and Ag content are the most effective parameters on wear behavior of coatings, respectively. The process was then modeled in Artificial Neural Network and the counters of parameters together with the outputs were determined. The results showed that wear resistance decreased with increasing both Ag content and current density.

The ZrC nanoparticles were synthesized by the sol-gel/carbothermal reduction method and then were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Afterward, the nanoparticles were loaded into the electroless Ni-P plating bath at concentration of 0.1 g. L-1. The SEM images showed that the nanoparticle incorporation causes to the decreasing of the coating nodule size. The cross-sectional SEM images showed the columnar structure of the coatings. Also, the nanocomposite coating showed higher thickness than the normal Ni-P coating. Energy Dispersive X-ray Spectroscopy (EDS) was used to confirm the incorporation of the nanoparticles into the coating. Also, the uniform distribution of the incorporated nanoparticles was confirmed by the EDS-mapping. The peaks corresponding to the ZrC nanoparticles were not seen in the XRD pattern of the nanocomposite due to high dispersion level of the nanoparticles in the coating. Electrochemical Impedance Spectroscopy (EIS) studies in 3.5 wt. % NaCl solution showed that the corrosion resistance of the electroless coating significantly improves by incorporating the ZrC nanoparticle so that the polarization resistance was increased from about 27.04 to 43.08 kΩ. cm2. The results of the potentiodynamic polarization tests at the same corrosive media showed that the corrosion current density value was decreased from about 1.70 to 0.87 μA. cm-2 after incorporation of the nanoparticles. Also, the Vickers micro-hardness of the nanocomposite coating was measured to be around 720 which was much higher than that of the normal electroless coating (468). Finally, the role of the electrostatic attraction in trapping of the ZrC nanoparticles into the matrix of the electroless coating was revealed by determination of charge type of the nanoparticles and alloy surface.

Cathodic arc physical vapour deposition is considered the industrial process for production of nitride coatings, but it suffers from micro-sized particles due to inherent characteristics of electric arc. Macro-particles exert undesirable effects on surface roughness, tribological properties, corrosion and oxidation resistance and, therefore, must be controlled. In the present study, these particles have been characterized and evaluated in three-component, TiSiN, and four-component, TiSiCN, coatings deposited on steel substrate in an industrial process. Energy dispersive spectrometry and X-ray diffraction indicated that chemical composition of the coatings were in the nominal ranges and TiSiN and TiSiCN had composite structures based on TiN and Ti(C, N) crystal lattices, respectively. According to the size and distribution of micro-particles, their roughness and morphology by field emission scanning electron microscopy, together with Image analysis, the particles were classified into three groups; most of them were spherical with an average diameter of 1 micron. EDS and X-ray mapping on the surface of coatings were carried out to assess the chemical composition and origin of the particles. The results revealed that increasing silicon content of the particles, as compared to the coating matrix, was associated with the formation of the particles from cast Ti-20Si target due to separation of Si in the microstructure and the lower melting temperature of silicon compared to titanium. The dominant cause in the formation of macro-particles is the heterogeneity of the target material together with the arc mobility; TiSiCN coating, with higher vapour pressure during deposition, experienced more particles and a higher roughness than TiSiN coating.

In this research, titanium carbo-nitride coatings were synthesized on the surface of Ti-6Al-4V alloy by nitro-carburizing route and the detachment mechanism of the coatings were investigated. For this purpose, rectangular blocks were embedded in a carbon containing graphite cup. Then, the cup was placed in a tubular furnace containing nitrogen gas. After coating in different temperatures between 1200 and 1400 ˚C for 20 to 60 min soaking times, structure and microstructure of the coatings were investigated by X-ray diffraction, Raman analysis and scanning electron microscope equipped with energy dispersive spectroscopy (EDS). Moreover, the effect of coatings on the corrosion resistance of the alloy in an aqueous solution containing 5.2 mol HCl, 3.2 mol HNO3 and 3.2 mol HF was investigated. Results showed that the maximum thickness of the titanium carbo-nitride coating for the sample treated at 1400 ˚C for 60 min was about 50 μm. However, the possibility of coating detachment increased with increasing the coating temperature. It was due to the formation of Al-rich layer at the interface of the coating and the substrate and the formation of Ti3Al brittle phases, as well as the difference between the thermal expansion coefficient of the coating and the substrate. Corrosion test results showed that the formation of the coatings decreased the corrosion rate of the Ti-6Al-4V alloy from 130g.m-2.min-1 for the bare alloy to 10g.m-2.min-1.

Application of WC-10Co-4Cr coating deposited by High Velocity Oxygen Fuel (HVOF) has been significantly developed in key parts of various industries, nowadays. These coatings are ground to achieve the desired surface roughness. In this study, the residual stress of as-sprayed and ground coating was determined by the X-ray diffraction (XRD) technique using sin2 method and finite element method(FEM). In the experimental evaluation, the chemical layer removal process was used to measure the through thickness residual stress. In the finite element analysis of the grinding process, the temperature distribution of workpiece is initially obtained by applying the thermal flux from the grinding process. Then the workpiece cools until it reaches the ambient temperature. The temperature history of thermal analysis is applied to the stress analysis and the final distribution of residual stress is determined by applying grinding forces and residual stress caused by the HVOF process. The results showed that there was a good agreement between the experimental and simulation results and after the grinding process, the value of compressive residual stress of coating surface increases was increased. Also, in the experimental and simulation investigation, the increase in compressive residual stress compared with the pre-grinding was up to 100 μm and 120 μm, respectively. There is no increase in compressive residual stress in the higher depth of coating and also in the interface of the coating and substrate.

The purpose of this study was to synthesis gelatin/silicon and magnesium co-doped fluorapatite nanocomposite coating and also gelatin coating on Ti-6Al-4V alloy in order to improve and modify the biological properties of this alloy. For this aim, nanocomposite coating and gelatin coating were first fabricated by dip-coating method. Then, the physical, corrosion and biological properties of the created coatings were investigated by different methods. The results indicated that a uniform nanocomposite coating with a thickness of about 6.26 microns was formed with appropriate structure and phases and increased roughness by adding nanoparticles to gelatin coating. Electrochemical measurements showed that nanocomposite-coated Ti-6Al-4V specimen with a polarization resistance of RP = 5.349×105Ωcm2 has higher polarization resistance in comparison with the gelatine coating with a polarization resistance of RP = 1.191×105 Ωcm2 and the non-coated specimen with a polarization resistance of RP = 5.2453×104 Ωcm2. The cytotoxicity test showed no cell cytotoxicity of the coatings. Also, cell growth and proliferation of the nanocomposite-coated specimen showed statistically significant difference compared to the non-coated sample. Cell adhesion to the nanocomposite-coated specimen was also much better than the non-coated sample and gelatin-coated sample.

AISI 430 ferritic stainless steel is used as interconnects in solid oxide fuel cells. In order to improve the oxidation resistance of steel in operating conditions of solid oxide fuel cells, protective coatings can be employed. In this study Ni-TiO2 coating was deposited on an AISI 430 stainless steel substrate by electrocodeposition in Watt’s plating bath containing TiO2 particles. Composition and properties of Ni-TiO2 coating were investigated as a function of current density. The volume percentage of embedded TiO2 was raised by increasing in current density until 4 A/dm2 and beyond that reduced. Also grain size of Ni-TiO2 composite coating decreased until 3 A/dm2 and above this current density, the again grain size raised. Maximum value of microhardness obtained in 4 A/dm2 current density. In order to investigate the oxidation resistance, coated and uncoated specimens were subjected to isothermal oxidation at 800 ºC for 300 h. Results showed that the coated specimens at the bath containing of SDS surfactant and without SDS surfactant had less mass gain compared to uncoated ones. The microstructure of composite coatings, before and after oxidation was investigated by scanning electron microscope (SEM) and X-ray systems.