IRANIAN JOURNAL OF SURFACE SCIENCE AND ENGINEERING
Year:2019 | Volume:14 | Issue:38|Papers Count:9

In this research, nanostructured Cr2O3 (C) and Cr2O3-20YSZ (CZ) coatings were deposited using Atmospheric Plasma Spray (APS) process and subsequently their mechanical properties including fracture toughness, hardness and bonding strength were evaluated and compared with each other. For this purpose, Cr2O3 and YSZ nano-powders were firstly prepared by high-energy planetary ball milling and then mixed in the given volume. To use the powder mixture in the plasma spraying, the powders were agglomerated and sprayed onto a 304L steel substrate. Microstructural studies of the powders and coatings were carried out through Filed Emission Scanning Electron Microscope (FE-SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. XRD patterns of the milled powders and the coatings indicated there was no newly-appeared phase during the milling and plasma spraying process. Porosity of the coatings was measured using an optical microscope by image analysis of their cross-sectional images. Mechanical properties evaluation showed that both coatings have high adhesive strength in the range of 43-49 Mpa. Although the addition of YSZ nanoparticles to the chromia coating slightly decreased the coating hardness, it caused a considerable increase in the coating toughness due to the zirconia transformation toughening mechanism.

In this study, a set of possible conditions for the addition of alumina to the thermal barrier coating system was considered, taking into account the experimental results reported by other researchers, from the point of view of the optimal state of adding the alumina to the thermal barrier coating system, in terms of increasing oxidation resistance and hot corrosion. The heat transfer and distribution of stress have been discussed and studied in a comparative and absolute manner. The results showed that in alumina-containing samples, the critical area of concentration of stress is in the interface of the layers containing alumina. Also, the maximum stress values in alumina-containing samples are higher than those with no alumina. Due to the higher thermal conductivity of alumina than YSZ, the addition of alumina to the thermal barrier coating system weakens the thermal insulation property.

In this experimental work Al doped tin oxide thin films with different composition of 5 to 10 mass percent of Al and 95 to 90 mass percent of SnO2 were deposited on glass substrates by electron beam evaporation technique. Then effects Al and thickness on the electrical, optical and structural properties of thin films were investigated. Properties of thin films have been studied using X-ray diffraction, UV-Visible spectrophotometer and four probe methods. XRD photographs were prepared and show the polycrystalline structure formation and preferred orientation (110). Also by increasing films thickness, optical transmission and resistivity are decreased. So that in the case of the films with 7. 5 mass percent of Al, the average transmission decreases from 88. 5 % for film with a thickness of 250 nanometer to 82. 3 % for film with a thickness of 450 nanometer and resistivity reaches to its minimum value of 5. 247×10-4   cm for the sample with a thickness of 450 nm.

In this paper, the effect of changing the spray distance in the high-velocity oxy-fuel (HVOF) spray method to apply NiCrBSi-WC(Co) coatings on the resulting microstructural changes and also on the mechanical properties of the coating (including adhesion strength, hardness and wear resistance) are discussed. The SS304 stainless steel sheet was used to make substrates. In the range of 200-300 mm, where the spraying distance was changed, with increasing spray distances, more suitable and homogeneous layered microstructure, having less porosity and less melted particles, as well as a better distribution of carbide particles in the coating structure, was obtained. The NiCrBSi-WC(Co) coating applied by HVOF gun at a distance of 300 mm indicated the most suitable structure meanwhile the highest adhesion strength to the substrate, the highest hardness, and the lowest wear rate.

In this article, the optical properties of Graphene/Au nanocubes have been studied for the different number of graphene layers on 1 or 2 faces of cubes. The extinction efficiency factor has been calculated in the near and far-field regime by the discrete dipole approximation (DDA) method. Our results show that the height of extinction's peak decreases significantly, by increases number of graphene layers on nanocube. Moreover, the wavelength of surface plasmon resonance peak redshifts from 516 to 700 nm (this peak is due to dipole formed alonge the polarisation direction), although the wavelength of the another peak stays constant about 230 nm(this peak is due to dipole formed perpendicular to the polarisation). In addition, with increasing size of nanocubes, the height of peaks decrease, the width of them increase and wavelength of plasmon peaks don't show any shifts for a constant thickness of graphene. The results of this study may be used for fabrication of biological sensors at vis wavelength.

For the first time, nitrogen gas was used in friction stir processing (FSP) to form an Al/AlN composite surface layer on aluminum plate. Investigating the microstructure of the layers by X-ray diffraction, scanning electron microscopy and optical microscopy showed the formation of aluminum nitride particles on the surface layer of commercially pure aluminum. These particles found to have non-uniform distribution in the layer. While the percentage of composite reinforcements is not more than 10%, the aluminum grain size reduced from 100 to 70 μ m due to restoring processes resulting from severe plastic deformation and significant improvement in surface properties observed. Due to extreme thermo-mechanical process, the surface layers have a finer grain size and high levels of hardness. As a result, the grain size ranged from an average of 100 μ m to 70 μ m and a hardness of 22 to a maximum of 38 Hv, which is about 1. 7 times the base metal hardness. The wear resistance of the sample also improved up to 1. 1 times with respect to fine graining of the surface layer and the presence of hard nitride particles. The coefficient of friction reduced from 1. 2 to 0. 9, indicating an improvement in the tribological properties of the sample.

In this study, by mechanical alloying method with a powerful bullet milling machine (SPEX) was used to create aluminum coating on the simple carbon steel surface (Ck 45) Balls with diameter of 4mm with a total weight of 50g and 5g aluminum powder with 99. 99% purity, the size of smaller particles than 150μ m and weight of 5g with (Ck 45) steel specimen were 8×8 mm with a thickness of 3mm were put into the milling chamber and milled for different times from 10min to 30h at room temperature. As-milled samples were annealed at 550˚ C at different times (2, 4, 6, 8, 10, 30h) to evaluate the formation of Fe-Al intermetallic compounds, and the effect of thermal treatment coating properties such as: adhesion rate, fuzzy changes thickness of intermetallic compounds surface were investigated. Structures of the produced coating were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), spectrometry and micro hardness test. The results showed that the best coating in terms of micro structural properties and uniformity was created after 80 min ball milling. The results of the thermal treatment at a constant temperature of 550˚ C for 30h showed that the interface between the aluminum coating and the steel substrate is formed and has a thickness of 28 micrometer. Furthermore the micro hardness test was carried out on the coated samples and results showed that the coating after the 80 min alloying, before thermal treatment had a low hardness of about 75 Vickers after performing the thermal treatment for 30h, the hardness of coverage in the interface of Fe/Al was increased to 471 Vickers.

In this paper, nanostructured CrAlN coatings were deposited onto steel substrates using an industrial cathodic arc physical vapor deposition (Arc-PVD) technique. Field emission scanning electron microscopy (FESEM) was employed to evaluate the microstructure and the phase analysis was carried out using Energy Dispersive Spectroscopy (EDS) and Xray diffraction (XRD) methods. The XRD patterns were used to determine the crystallographic texture of the coatings and the results showed (222) as the dominant texture. Moreover, it was found that all coatings had nanocrystalline structure with crystallite sizes between 8-18 nm. CrN was found to be the dominant phase in the XRD patterns; addition of aluminum produced CrAlN, leading to shifts of the diffraction peaks. Cr2N and AlN phases were identified by the XRD pattern which can be attributed to the decrease of the nitrogen pressure down below a critical value and the increase in the evaporation of aluminium, respectively. The change in the Al content of the coating and the subsequent displacement of the diffraction lines caused a challenge in the phase identification procedure. Therefore, identifying the existing phases in the coating was not feasible merely by the EXPERT software since CrAlN is not defined in its database; the crystal phase data of the nitride coatings must be used for accurate phase identification.

The art of Safavid period has always been the rich and valuable arts of the Iran which has a great important in art of Islamic period. Among the remaining monuments and relics from the Safavid period in Isfahan, Naqshi-i Jahan square is of particular importance in which M asjid-i Iamā m has outstanding artistic features. So, numerous studies have been carried out on different aspects of this M asjid. However, one of the most prominent features that has not been investigated is the main door of the mosque and its metallic facing. The aims of this paper are to identify the alloy composition, manufacturing and gilding technique that have been used in metallic door facings of M asjid-i Iamā m, Isfahan, in order to recognize the Safavid metalwork. For this purpose, different parts of the door were sampled and analyzed by SEM-EDS, ICP-OES and also M etallography. The results showed that an alloy of silver and copper has been used in manufacturing of metal sheet of the door. Also a very few amounts of arsenic, zinc and lead were identified in the alloy composition, which can be related to the ore extraction and cupellation process. Slip lines and twins were identify in the microstructure of the silver sheet. Accordingly, metallographic investigation showed that thin silver sheet have been made by hammering and annealing. In addition, the fire gilding (amalgam gilding) was distinguished as surface decorating technique. The presence of mercury in the gold layers and the porosity in the gold layers confirmed the use of amalgam gilding.