فصلنامه علوم و مهندسی سطح ایران
پیاپی 21 (پاییز 1393)

Bioglass coatings on metallic implants have two important effects: intimate link between bone and implant، corrosion protection of metallic implants in body fluid and protection from tissues in front of corrosion products. In this research، first، 45S5 bioglass- silica double layer coatings were prepared on 316L stainless steel by sol-gel procedure and then corrosion and bioactivity behavior of coatings in simulated body fluid solution was evaluated. The results show that uniform coatings are prepared on substrates that increase the corrosion resistance of stainless steel substrates. Also، the obtained coatings are bioactive due to the formation of hydroxyapatite on them after 30 days of immersion in simulated body fluid solution.

In this study the experiments was done in order to product silicide component as a protective coating with a mixture powder Mo-Si-C In situ cladding on the nickel surface. Before applying cladding، was ball-milling processes for activating mixture powder and then by the product using electrodes of powder mixtures by doing welding processes was formed coating with a thickness of 1mm by sharp boundary with substrate. The cross-section microstructure of specimens was studied by optical microscopy and scanning electron microscopy (SEM). The specimens were characterized by X-ray Diffraction (XRD). Phase detecting specimens indicate that the addition of 2wt% graphite powder to the mixture formed Mo2Ni3Si، NiSi and small amount of MoSi2 phase and SiC reinforcement phase. Evaluation the results of the reciprocating wear tests showed that by addition 2% weight graphite in the mixed powder and formation SiC، the good resistance abrasion is done to change the plastic form and loss weight during the wear process. Also the hardness test showed that by the cladding of mixture powder increases hardness to 850 HV0. 2.

In this study، the electrochemical behaviour of pure commercial Ti in 0. 1، 1. 0 and 3. 0M H2SO4 solutions has been examined. The polarization curves suggested that pure commercial Ti showed excellent passive behaviour in 0. 1، 1. 0 and 3. 0M H2SO4 solutions. Mott–Schottky analysis showed that passive films formed on pure commercial Ti، are n-type semiconductor. For three solutions، Mott–Schottky analysis showed two positive slopes in the passive region. Also، this analysis indicated that the donor densities (ND1 and ND2) are in the range 1020 cm-3 and increased with solution concentration. Based on the EIS analysis، it was shown that the polarization resistance decreases with solution concentration.

In this work، in order to introduce new with low cost supply coatings in thermal spray industry، high carbon ferrochromium and low carbon ferrochromium coatings were applied on plain carbon steel (CK45) by air plasma spray. Microstructural properties and wearbehaviour were investigated. Microstructure of coatings were analyzed by scanning electron microscope، their phases were recognized by X-ray Diffraction and also hardness was investigated by Vickers indenter method. The results indicated that the coatings with the lower argon gas flow rate had better properties due to longer thermal stability at high temperature. The dominant wear mechanism in HCFeCr was identified as adhesive wear with microcracking with different severity. It is found that delamination mechanism was the predominant wear mechanism for LCFeCr coating.

Excessive growth of surface oxide scale with high electrical resistance accompanied by spallation and chromium poisoning of the cathode are the main disadvantages of using metallic interconnects in SOFCs. The mentioned limitations reduce the interconnect lifetime and the efficiency of SOFC. Deposition of a protective coating onto interconnect is the best method to overcome the problems. Chromium-free spinels are promising materials among which Co-Mn spinel has been given a great deal of attention due to good electrical conductivity and suitable diffusion barrier against chromium. In this research، a duplex layer of Co and Mn were deposited on AISI-430 ferritic stainless steel to produce a protective/conductive coating by pulse electroplating. Post heat treatment in air at 800°C lead to inter-diffusion of Co and Mn as well as oxidation. Consequently، Co-Mn spinel coating formed on the surface. After 100 hours of oxidation، negligible Cr content (less than 0. 5%at.) was detected in the coating. Hence، applying this coating can properly control the Cr-evaporation phenomenon by preventing chromium diffusion towards the surface. Moreover، According to the XRD results، FeCrCoO4 and Mn (CrCo) O4 spinels with higher electrical conductivity than chromia are formed at the coating/substrate interface.

Hydrophilicity of nitrogen-doped TiO2 nano thin films were studied. Samples were synthesized by spray pyrolysis method. Annealing temperature، which has an important role in nano thin films structure، was 450oC. It was seen by increasing of N، hydrophilicity of the samples under UV irradiation increased. Hydrophilicity of four samples was higher than pure TiO2. Due to increasing of N band gap decreasing and increasing of roughness and grain size were observed.

In this study, a different method which is based on dissolution of substrate i.e. the early stage of phosphating and its effect on the characterization of formed layer in the second step of phosphating was investigated. This method that called two steps phosphating has obvious influence on the formation of dense and very fine crystalline zinc phosphate coating on the plain carbon steel. Dissolution of base metal during initial phosphating and entrapping the small particles of the initial phosphate coating, during removing of phosphate layer with grinding, increases the number of nucleation sites on the surface. Considering time consuming and cost constraints of grinding in industry, in this paper the possibility of using sand blasting operating as a substitution method for removing initial coating was studied. On the other hand, according to the results of corrosion tests such as salt spray, polarization and electrochemical impedance spectroscopy (EIS), improved protective properties have been achieved for the denser coating which is formed by the introduced method. Also, the results of dry and wet adhesion of two diverse paint types, air-drying paint (epoxy systems, polyurethane) and oven coating (alkyd - melamine (Series YS)), showed improving paint adhesion for formed phosphate layer by this innovative method.

In this paper, nucleation stage and bulk growth of Ni nanostructures deposited under oblique angle of 75˚-85˚ by using kinetic Monte-Carlo method are simulated. Substrate temperature effect on shape, size, and columns distribution are studied as well. At bulk growth stage, by definition local potential barrier and random thermal energy, Ni nanostructures growth at three zone temperatures which is in the range of T/Tm<0.45, (T is substrate temperature and Tm is material melting temperature) are studied. Our results showed that at range of T/Tm<0.3 structures are grown as thin column and dome shape on the top. With increasing temperature, in the range of 0.3 Keywords: Oblique angle deposition, Nanostructures growth, Structure zone model, Substrate temperature, Shadowing effect, Surface diffusion