فصلنامه علوم و مهندسی سطح ایران
پیاپی 14 (تابستان 1391)

Indium Tin Oxide (ITO) thin layers were deposited on glass substrates by electron beam evaporation technique using a various mixtures from 60 to 95wt% indium oxide and 40 to 5wt% tin oxide. Aftter deposition, the films were annealed in air for 3h at 450ْC. The effect of dopant concentration on structural and optical properties of these layers were investigated. It was observed that by increasing of dopant concentration to 20wt%, band gap and grain sizes were increased. The highest energy gap and highest grain size were evaluated to be 3. 71eV and 23nm, respectively in the layers with 20wt% tin oxide.

Effects of different concentrations of potassium permanganate, as a corrosion inhibitor, on morphology, composition, thickness and corrosion behavior of anodic film of 2024-T3 aluminum alloy formed in 17% sulfuric acid were investigated. Surface morphology and chemical composition of oxide film were studied using field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were conducted to assess the corrosion performance of the coatings. These analyses have shown that presence and addition of potassium permanganate during anodizing process results in more compact and thicker anodic film with smaller pore size. In addition Corrosion results have shown that using permanganate ions increased corrosion resistance of the anodic layer, increasing the potassium permanganate in anodize solution, would caused a coating with higher corrosion resistance. The quantity of the corrosion improvement was about 25% and 85% for 0.01 and 0.1M, respectively.

By increasing use of very small structures, thin films, functionally graded materials, nanocomposites, and heterogeneous surfaces in various engineering areas the conventional tensile and compression tests cannot be readily used for measurement of the viscoelastic relaxation modulus and creep compliance of such materials. Recent developments in the indentation contact analysis for viscoelastic bodies, an exact evaluation of relaxation and creep characteristics of viscoelastic solids has been prepared to use the nanoindentation. In this paper, after representing the measurement methods of elastic properties for the polymeric films and layers, a powerful mathematical approach, based on contact mechanics, was developed to describe viscoelastic characteristics directly by using the novel nanoindentation technique. Independently, a constant-rate displacement and a constant-rate loading histories were used to measure the creep compliance and relaxation modulus from nanoindentation tests, respectively. The viscoelastic moduli, using the viscoelastic contact theories, have been extracted to the nanoindentation load-displacement data. A generalized Maxwell model and a generalized Kelvin model were used to describe the creep and the relaxation constitutive behaviors of viscoelastic layers, respectively.

Chitosan has received considerable attention for biomedical applications in recent years because of its biocompatibility and biodegradability. Chitosan membranes with 30 μm in thickness were prepared and modified using Ar ion. Membranes were bombarded by using three energy levels, 30, 55 and 80 keV with fluxes of 1× 1015, 3×1015 and 5 × 1015 ion/ cm2. The influences of the ion bombardment on the basic properties of the membranes, namely morphology, water permeate flux and hydrophilicity was investigated. Atomic force microscope (AFM) images showed that ion bombardment increased surface roughness, while attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrum revealed an increase in surface polar groups, which was consistency with a decrease in water contact angle. The results indicated that Ar ion bombardment can markedly improve the surface hydrophilicity of the chitosan membrane. In addition, chitosan membranes after Ar ion implantation, found antifungal property.

Carbon nanotubes (CNTs) have super-strong mechanical characteristics and unique hollow nanotube structure and were believed as ideal materials for fabricating the excellent composites. In this study, Ni-P-CNT composite coating was successfully deposited on the surface of copper by electroless plating. Hardness of composite coating was compared with Ni-P coating, before and after heat treatment. The x-ray diffraction (XRD) analysis, EDS analysis and the scanning electron microscopy (SEM) were used to characterize coatings. Wear behavior of coatings were investigated using a pin-on-disk test rig and friction coefficient were reported. Results showed that incorporation of CNT in coating result in increasing of wear resistance and decreasing of friction coefficient to 7 and 2 times, respectively. Improvement of Ni-P-CNT tribological behavior could attributed to strong mechanical characteristics and unique topological structure of nanotubes.

In this study optimal thickness of WC-Co spray coating by HVOF (High Velocity Oxy Fuel) method on the surface of hot rolling pinch-roll roller by utilizing finite element method were investigated. The task of pinch-roll was to get and guide sheets toward the coilers. The working environment of these components was acidic and they worked in temperature and humid ambient. The surface of these rollers was worn due to impact and movement of sheet on it. At first, the critical condition of pinch-roll was determined. Results showed that working condition of the pinch-roll at the initial impact was worse than other working times. Also hard and thin sheets made the more critical condition. After the surface of pinch-roll was coated analysis showed that deformation and failure were created in coating. In this condition the best thickness of coating was about 600 microns that caused minimum shear stress distribution both in the surface coating and in the interface of coating/substrate.

Plasma nitriding could improve the lifecycle of plastic mould steels by modifying the surface layers. In this study, the effects of time and temperature of plasma nitriding on plasma nitriding behavior of plastic injection moulding steel P20 were studied. In this regard, pulsed plasma nitriding treatment was performed on P20 samples at different processing temperatures such as 450, 500 and 550 ºC for 2.5, 5, 7.5 and 10 h at gas mixture of 75% N2 - 25% H2. Diffusion zone and compound layer were studied by optical and scanning electron microscopy and the crystallographic phases on surface were determined by X-ray diffraction analysis. Also, micro hardness changes from surface to core of the samples were determined. Results have shown that by increasing treatment temperature and time, nitrided layer thickness and hardness were increased respectively. The SEM results showed that the interface of the compound layer and the diffusion layer formed on the sample treated at higher temperatures were more uniform than those treated at lower temperatures. Regarding the results of EDS, during the ion nitriding of P20 upward diffusion of the carbon and the downward diffusion of the nitrogen have been occurred. XRD results have shown that in all the process parameters ε-nitride was the most forming phase.

One of the most important methods to prevent the failure of materials in high temperatures is using thermal barrier coatings (TBC). Hot corrosion is the most important reason of thermal barrier coatings failure. Synthesis of an interface composite layer between bond coat and top coat could be so useful to increase their hot corrosion resistance. In this study, hot corrosion behavior of two kinds of TBC synthesized by APS were investigated: 1) Common TBC (MCrAlY, YSZ) 2) Multi layers FGM (Functionally graded materials), TBC (MCrAlY, 50%YSZ+50%MCrAlY, YSZ). Hot corrosion tests were carried out on the coatings surface in the molten salt of 45%Na2SO4+55%V2O5 mixture at 1050 °C for 20 hours. Microstructure, morphology and chemical composition of the surface and cross section of the coatings were investigated by SEM equipped with EDS. XRD analysis was used to study microstructure and hot corrosion products. The results indicated that the hot corrosion resistance of FGM, TBC was much better than normal TBC due to the formation of AlVO4 and CrVO4 phases in this kind of coating during the hot corrosion test.

Zirconia based thermal barrier coatings (TBCs) were extensively used in gas turbines engines to protect and provided thermal insulation for hot-section metal components. Consequently, the key parameter of these coatings is low thermal conductivity. The present paper deals with evaluation of effect of the microstructure and stabilizer type on zirconia based TBCs thermal insulation capability. For this scope, three type of coatings including conventional yttria stabilized zirconia (YSZ), conventional ceria and yttria stabilized zirconia (CYSZ) and nanostructured yttria stabilized zirconia have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738 substrates. Microstructural evaluation and phase analysis were performed using field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) respectively. Result srevealed that with employing of ceria stabilizer and fabrication of nano-structure in coating, the thermal insulation capability of zirconia based TBCs were enhanced.