IRANIAN JOURNAL OF SURFACE SCIENCE AND ENGINEERING
Year:2017 | Volume:12 | Issue:31 |Papers Count:11

In this study, initially maghemite (g- Fe2O3) nanoparticles were synthesized by using of the chemical co- precipitation technique and then the deposited samples were annealed on white glass at the temperatures of 400, 450, 500, 550 and 600°C by spray pyrolysis technique. Their optical properties were investigated by Ultraviolet-visible (UV-vis) spectrometer and structural properties of samples were characterized by infrared (IR) spectrum and X-ray diffraction (XRD). Surfaces morphology of samples was investigated by scanning electron microscopy (SEM) technique. The results obtained from this study show that by increasing the annealing temperature of the nanoparticles, the particle sizes have grown. This is due to decreases in optical band gap in annealed samples of maghemite nanoparticles. Percent of wavelengths absorbance in the ultraviolet region has been decreased and has been shifted toward visible. Moreover, crystalline structures of materials have been more regulated and deformed from hunk shape to spherical shape.

In this study, high-velocity oxygen-fuel (HVOF) process was applied to produce StelliteWC composite coatings on the surface of carbon steel samples. For this purpose, various amounts of WC powder 0%, 10%, 20% and 30% were mixed with Stellite6. The structural and mechanical behavior of the coatings were evaluated using X-ray diffractometry, scanning electron microscopy, microhardness and roughness test. The results showed that the micro structure of the coatings were composed of a cobalt and chromium solid solution dendritic structure with the interdenderitic phases of cobalt enriched phase, carbides and WC particle. The XRD evaluations indicated that the coatings included Co-rich phase, CoCx, Co3W3C, Co6W6C as well as Cr23C6 and Cr7C3 carbides. Also, It was found that the hardness was increased, the adhesion was improved and the porosity was decreased by increasing the tungsten carbide as reinforcement.

In this study, Cu-TiO2 nanocomposite coatings were electrodeposited from a copper sulfate bath containing dispersed TiO2 particles of 20 nm mean size. These coatings were prepared under pulse current condition on steel substrate in room temperature. The influence of pulse frequency and average current density on the microstructure and incorporation of TiO2 nanoparticles in coating were investigated by scanning electron microscopy (SEM) and (EDS) analysis. The crystallite size of the coatings calculated from the x-ray diffraction patterns using the Scherrer equation. Micro hardness of the coatings was assessed using a Vickers micro-indenter. Performance of the coatings was investigated by the potentiostatic polarization method. Process parameters were optimized with respect to TiO2 content of the composite coating and micro hardness. The optimized pulse frequency and average current density were 20 Hz and 2 A/dm2 respectively. The amount of TiO2 particles incorporated into the coating that were produced under the optimum plating conditions was 1.9 wt. %; also, the crystallite size of this coating was 27 nm, the micro-hardness was 180 Hv and the corrosion rate was 0.56 mpy.

In this study, surface hybrid composites reinforced with TiC and MoS2 were fabricated on heat treated aluminum 7075 substrate via friction stir processing (FSP). For this purpose, reinforcement particles were added to the aluminum 7075 matrix using groove technique, afterward friction stir process was applied using three passes. To evaluate the wear behavior of fabricated composites, reciprocating wear test was applied. Scanning electron microscopy (SEM) was utilized to study wear track and wear particles in order to determine the dominant wear mechanism. The effect of friction stir process on hardness and tribological behavior of aluminum 7075 alloy was studied. The results showed that because of the existence of MoS2 reinforcement particles as solid lubricant, wear resistance of Al7075/TiC/MoS2 surface hybrid composite was significantly improved in comparison with Al/TiC composite samples. It was concluded that abrasive wear mechanism was the dominant mechanism in Al7075/TiC surface hybrid composites. The highest hardness was observed in Al7075/TiC surface hybrid composite, which may be due to the lower hardness of MoS2 particles as solid lubricant in Al7075/TiC/MoS2 surface hybrid composites.

In this research, alumina– titania nanoparticles in thin-film forms in different alcoholic environments such as ethanol, butanol and isopropanol were coated on st12 steel substrates by electrophoretic process and coating operations was performed at different voltages, as well as chronoamperometry method has been used to investigation of the mechanism of nucleation and surface qualities of coatings. in the measurment the weight of the coating test showed that the weight of the coating increased via increasing voltage as well as in the measurement results of coatings weight and their quality viewing showed that coating weight changes with voltage (electrical field intensity) and time follow the hamaker relationship. morphology of the synthesized coatings were evaluated by using the field emission scanning electron microscope and the average thickness were determined through the mip metallography application. the corrosion behavior of uncoated steel and coated steel samples has been evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy tests.

In this paper structural and electronic properties of AgGaX2 (X=S, Se) compounds in bulk and its nanolayers in [112] direction were calculated by using Full Potential Linear Augmented Plane Wave (FP-LAPW) based on density functional theory. The studied nanolayer were confined in the orthorhombic supercell and simulated in [112] direction. All calculations were done by applying the periodic boundary condition along nanolayer surfaces, for example x and y Cartesian coordinate and enough vacuum were provided to isolate the system from its neighbors. For investigation of structural and electronic properties of bulk and nano-layers several approximation were used and the results were in good agreement to the experiment and all materials were semiconductors. The effects of dangling bonds and nanolayer thickness on the electronic properties were explored, also cohesive energy were calculated to investigate the structural stability.

Amorphous, nanocrystalline and mixed amorphous-nanocrystalline Co-P coatings were successfully coated on St37 via DC electroplating method using various phosphorous (P) content in coating compositions. In addition to phosphorous content, heat treatment caused structural changes of the alloy coatings. The effect of changes in the P content and hence phase structures were studied prior and post heat treatment on the hardness and wear resistance of the coating. A scanning electron microscope (SEM) with high resolution (HR-SEM) equipped with an energy dispersive spectroscope (EDS) and an X-ray diffraction (XRD) system were used to study the surface morphology and phase structure as well as the chemical composition of the coatings, respectively. Micro-hardness and wear resistance of the coatings were measured via Vickers hardness system and pin on the disc test, respectively. The results showed that by increasing P content, the coating micro hardness was in turn increased due to a remarkable enhancement of the hardness of the solid solution and that was applicable for the coatings after heat treatment because the interstitial phases productions. In the beginning and prior to the heat treatment by increasing the P content up to 5.6%, the wear behavior of the coatings was improved substantially, while at further P content, the wear result started to decline. However, after heat treatment, there was a direct relationship between the wear resistance and P content. Also the maximum hardness and wear resistance belonged to the amorphous coatings after heat treatment.

Ti-6Al-4V titanium alloy due to strength to weight ratio and corrosion resistance has many applications in aerospace industries. However, this alloy shows poor wear resistance especially under high loads. In this article, with the aim of improvement hardness and wear resistance of Ti-6Al-4V titanium alloy, B4C hard particles has been added to the molten pool in TIG welding process. Microstructural investigations via XRD and SEM showed that B4C particles almost completely solved in titanium matrix and with the arrival of boron and carbon in molten titanium, phases based on TiB and TiC has been formed. Phase morphologies based on TiB was blade and eutectic shape and TiC phase was spherical like. The results showed that surface hardness is equal 1020 Vickers that is approximately 3 times more than the bare alloy.

An electrophoretic deposition process as a high-speed process of ceramic body shaping has received great attention in recent years and many kinetic equations from 1940 attempt to predict the yield of the process. In the development of these relations two major issues are taken into consideration: 1- Using constant current and 2- constant potential, each of these, led to a set of assumptions in the development of relationships. In all these efforts validation was based on a series of deposition tests is done at regular intervals (non-online or off-line). With the development of new systems, these tests can be done in the on-line process, which this method will result in the deletion of some errors in the system. By eliminating these errors there became clear that some considered assumptions in the development of relations were be ignored for long times and causes some errors. The relationships that have been developed based on the electric current of the cell will have less of errors. Because the sensitivity of the electrophoretic deposition process to the electric field changes inside the suspension that is the main driver of the process. finally, It was found that by taking account the electrical current of cell in the equation of Ferrari et al. there was be a new kinetic relationship that were honest in the constant electric potential and constant electrical current.