Showing 34 results for Coating
M. H. Fathi, Gh. Feizi, Sb. Moosavi, Gh. Gahanshahi, M. Salehi, A. Saatchi and V. Mortazavi,
Volume 20, Issue 1 (7-2001)
Abstract
Hydroxyapatite coatings have been used on metallic substrates in a variety of applications, including modifying the surface of human implants, bone osseointegration and biological fixation. In this paper, the effects of various kinds of metallic substrate on clinical and pathological results of in vivo tests are presented. Four kinds of endodontic implants i.e, stainless steel, cobalt base alloy, plasma sprayed hydroxyapatite coated stainless steel, plasma sprayed hydroxyapatite coated cobalt base alloy were prapared and implanted in mandibular canine of
cats. After a healing period of 4 months, investigation by SEM and histopathological interpretation and evaluation showed significant differences in tissue response and osseointegration between coated and non-coated metallic implants. It was concluded that the results were affected by the kind of metallic substrate .
Keywords: Hydroxyapatite coating, Dental endodontic implant, Osseointegration, Corrosion, Stainless steel,
Cobalt base alloy
K. Raeissi, A. Saatchi and M. A. Golozar,
Volume 23, Issue 2 (1-2005)
Abstract
On electropolished steel at low current densities, morphology and texture of electrodeposited zinc were investigated. Zinc coating is consisted of hexagonal crystallites laid on each other to produce packets. These packets are of different sizes and are stacked in different orientations to construct a homogeneous coating on steel substrate. This coating does not have texture, i.e., it has a random texture. With increasing current density, the morphology changes completely as each grain attains a special orientation. In this case, coating has a strong basal plane (0002) along with low angle planes (1013 and 1014). Coating obtained on mechanically polished surfaces consists of individual packets of zinc crystals, which are near each other with different
orientations. These coatings have a higher density of basal plane (0002) in comparison to electropolished surfaces. The morphology and texture variations with cathodic polarization and surface preparation of steel are due to their effect on nucleation and growth.
K. Zangeneh Madar and S. M. Monir Vaghefi,
Volume 23, Issue 2 (1-2005)
Abstract
In the present stady, thermochemical treatment in H2/NH3 atmosphere was used as a post-treatment for electroless Ni-P coatings on the AISI 4140 steel substrates. High phosphorus (9%) coatings with thicknesses of 2, 24 and 48 m were applied and the effects of the thermochemical treatment on the morphology, structural changes, roughness, hardness
and wear resistance of coatings were studied by SEM, EDS, XRD, profilometry, and microhardness tester. Wear test was used to evaluate wear characteristics of coatings. The wear behaviour of the thermochemical treated/Ni-P coated samples was assessed by comparison with thermochemical treated/uncoated (nitrided) samples. The results showed that effect of thermochemical treatment varies with the coating thickness. In addition, it was shown that a multicomponent coating containing phosphide, nitride and intermetallic phases as well as diffusion region can be developed in the thin (2 m) electroless Ni-P coated steel by thermochemical treatment. This sample showed better wear resistance than 24 m Ni-P coated steel under higher load. This behavior was ascribedto nitride phases formed at the surface as well as a nitrogen diffusion zone at the subsurface of thin Ni-P coated steel
A. Nasr-Esfahany and M.heydarzadeh Sohi,
Volume 23, Issue 2 (1-2005)
Abstract
Zinc-Nickel electrodeposits have been widely adopted for surface treatment of automobile steel sheet for high corrosion resistance. In this work the effect of pulse parameters on the Zn-Ni alloy electrodeposits was investigated. The hardness, thickness, corrosion resistance and composition of deposits thus produced were investigated. The surface topography of the deposits was also observed in SEM and results are reported. It has been shown that the thickness of the pulse electrodeposits
was almost even. The hardness in the pulse electrodeposits increased by increasing the on-time period and by decreasing the current density. It was also noticed that increasing the on-time period increases the nickel content of the deposit. Pulse electrodposits had fine structure and the structure become finer by reducung the on-time period and pulse frequency. The corrosion dehaviors of the deposits were then investigated. The results showed that the corrosion resistance of the DC electrodeposits improves in their nickel content increases. Pulse electodeposits show the same behavior, but deposits with about 13% nickel show maximum corrosion resistance.
A. Maghzian, A. Monshi, M.h. Fathi,
Volume 29, Issue 2 (12-2010)
Abstract
In the last decade, Calcium Titanate has been introduced as a bioceramic with acceptable mechanical and biological properties for orthopaedic implant applications. In this study, CaTiO3 nano-structure coating was produced by sol-gel dip-coating route for biomedical applications. Calcium nitrate and titanium isopropoxide were used as a precursor. After coating process, the specimen was subjected to rapid thermal annealing (RTA) at 800°C. The phase structure, functional groups and surface morphology of coating were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Uniform crack-free nano-structured coatings were obtained with perovskite crystal structure.
M. Mazrooei Sebdani, M. H. Fathi ,
Volume 31, Issue 2 (12-2012)
Abstract
Despite excellent bioactivity of bioactive ceramics such as hydroxyapatite, their clinical applications have been limited due to their poor mechanical properties. Using composite coatings with improved mechanical properties could be a solution to this problem. Therefore, the strength of metal substrate and the bioactivity of the improved composite coating combined could yield suitable results. The aim of this work was fabrication and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coating. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to coat on 316L stainless steel (SS) by deep coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) techniques were used to investigate the microstructure and morphology of the prepared coating. The results obtained from XRD analysis showed that the suitable temperature for calcination is 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite size of composite coatings determined via AFM was lower than 100 nm. Overall, the results obtained from this work indicate that hydroxyapatite-forsterite-bioactive glass nanocomposite coating can be a good candidate for biomedical applications.
F. Shahriari, F. Ashrafizadeh, A. Saatchi,
Volume 31, Issue 2 (12-2012)
Abstract
Although titanium has been recognized for its excellent bio-compatibility with human tissues and good corrosion resistance in some specific environments, little attention has been paid to the surface enrichment of the components by titanium. In this paper, titanium diffusion coating was formed on the surface of Ni-based alloy B-1900 via pack cementation technique and the microstructure of the coatings obtained was studied. Diffusion titanizing was carried out via pack cementation technique at 850 and 950 C for 3 hours in a mixture of commercially pure titanium, Al2O3 and NH4Cl powder. Microstructure, phase composition and concentration profile of the coatings were examined using optical and electron metallography, X-ray diffraction, and glow discharge optical spectroscopy. The results showed that Ti2Ni and AlNi2Ti were the main constituents of the coating. The formation mechanism of the coatings was also evaluated.
B. Bakhit, A. Akbari,
Volume 31, Issue 2 (12-2012)
Abstract
Composite and nanocomposite Ni-Co/SiC coatings were synthesized by electro-codeposition of micro and nano-sized SiC particles with average diameter of 10m and 20nm using horizontal electrodes. Surface morphology, chemical composition, phase composition, hardness and corrosion resistance of the deposited coatings were studied using SEM observations and EDX, XRD, microhardness and polarization measurements as a function of the electrodeposition current density. The results indicated that the nanocomposite coatings exhibit higher hardness and corrosion resistance compared with the composite coatings containing micro-sized SiC particles despite their lower percentage of the SiC content. The maximum hardness values of 615HV and 490HV were obtained for nanocomposite and composite coatings deposited at current density of 3A/dm2. The observed properties were discussed based on the structural details.
M.tahriri, F. Moztarzadeh, M. Raz , M. Ashuri,
Volume 32, Issue 1 (6-2013)
Abstract
In this study, magnetite (Fe3O4) nanoparticles were synthesized by chemical co-precipitation from the solution containing iron salts in alkaline medium under N2 gas and room temperature. Magnetite nanoparticles were characterized by X- ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), Brunauer-Emmet-Teller (BET), and vibrating-sample magnetometer (VSM). The rheological properties of magnetite ferrofluid were examined by rheology apparatus. The biocompatibility and cytotoxity of magnetite nanoparticles were evaluated by 3T3 and fibroblast cells. The results showed that the Fe3O4 magnetite nanoparticles coated by polyvinyl alcohol (PVA) could be an appropriate candidate for biomedical applications.
Z. Ansari, M. Alizadeh, A. Sadeghzadeh Attar,
Volume 33, Issue 2 (3-2015)
Abstract
In this study, mixed metal oxides Al2O3/MgO/TiO2 coatings with Al/Mg/Ti ratios of 5:1:3 and 2.5:3:4 were coated on AA1100 aluminum by sol-gel method. The surface morphology, phase analysis and the corrosion behavior of the Al2O3/MgO/TiO2 coatings were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and electrochemical impedance spectroscopy measurements (EIS) in 3.5 wt.% NaCl solution. The thermal behaviors, the bonds configuration, and functional groups of the coated samples were studied by thermo-gravimetric and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FTIR), respectively. The results demonstrated that heat treatment at
450 °C caused an increase in porosity and coating cracking, finally leading to the decrease of corrosion resistance. The best corrosion resistance was achieved for the sample with Al/Mg/Ti molar ratio of 5:1:3 without any heat treatment. The structure of this sample was amorphous, and heat treatment resulted in crystallization and decrease of the corrosion resistance.
M. Haerifar, M. Zandrahimi,
Volume 34, Issue 1 (5-2015)
Abstract
In the present study, 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn-Cu alloy coatings from a bath containing ammonium sulfate. The effects of current density on the microstructure, crystallographic structure, and chemical composition of the deposits were studied. The results showed that at low current densities, discontinuous coatings with a large amount of Cu can be obtained. Further increase in current density resulted in amorphous, compact and heterogeneous coatings with a small amount of Cu. The presence of Cu at low contents in precipitated coatings delayed the phase transformation of as-deposited ductile g-Mn to the brittle and hard a-Mn. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities.
M. Fazel, M.r. Garsivaz Jazi1, S. Bahramzadeh, S.r. Bakhshi, M. Ramazani, A. Bahramian,
Volume 34, Issue 1 (5-2015)
Abstract
Ni–SiC composite coatings are successfully employed as a protective coating in the inner walls of engine cylinders. In this study, Ni-SiC, Ni-SiC-MoS2 and Ni-SiC-Gr composite coatings were prepared from a sulfamate bath. Both mechanical and ultrasonic stirring were used simultaneously during the process. Taking into account the working temperature of engine cylinders, the wear behavior of coatings was evaluated at 25 to 300 ºC and the high temperature tribological properties of the coatings were investigated. Based on the results obtained from the wear tests, all three coatings showed almost good friction coefficient values at 25 and 100 ºC, which were close to each other. By increasing the temperature to 200-300 °C, the friction coefficient and weight loss values strongly increased. However, addition of solid lubricants caused the values to decrease. The Ni-SiC-Gr coating at all temperatures showed a good and stable behavior.
S. Bassaki, F. Golestani Fard, R. Naghizadeh, M. Rashidzadeh,
Volume 34, Issue 3 (12-2015)
Abstract
Titanium dioxide-nickel oxide porous coatings were synthesized by Plasma Electrolytic Oxidation (PEO)/ ElectroPhoretic Deposition (EPD) in one step and within a short time. The main purpose of this research was to increase photocatalytic activity of titanium oxide by increasing surface area and coupling of titanium oxide with nickel oxide. Applied voltage effects on phase structure, surface morphology and photocatalytic efficiency of coatings were studied. Phase structure and surface morphology of the synthesized catalysts were investigated by XRD and SEM, respectively. Photocatalytic efficiency of the samples was studied through measuring the decomposition rate of 4-chlorophenol. The results showed that the coatings mainly consisted of anatase and nickel oxide phases whose amounts in coatings increased with the voltage. There was an enhancement of the photocatalytic efficiency in TiO2/NiO composite coatings compared with TiO2 coatings. Besides, there was an optimum amount of NiO to reach maximum photocatalytic efficiently.
M. Bahrami, G.h. Borhani, S.r. Bakhshi, A. Ghasemi,
Volume 35, Issue 3 (12-2016)
Abstract
Organic–inorganic hybrid coatings were prepared by sol–gel method and deposited on aluminum alloy 6061. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) were used for structural study of the hybrid coatings. Adhesive strength of sol–gel coatings to the substrate was evaluated quantitatively and qualitatively. Corrosion behavior of the samples was studied by cyclic potentiodynamic and linear polarization tests. Results showed that adhesion strength of the coatings to the substrates was increased with increasing tetrapropoxide of zirconium (TPOZ) and cerium content. Corrosion tests showed that corrosion current density of coated samples were decreased three to seven orders of magnitude in comparison with uncoated aluminum alloy 6061. Decreasing in corrosion current density and increasing in polarization resistance was observed by increasing zirconia and cerium content. Unlike the uncoated aluminum alloy 6061, the crack-free coatings did not show pitting tendency.
M. Pourkarimi, B. Lotfi, F. Shahriari Nogorani,
Volume 35, Issue 4 (2-2017)
Abstract
In this study, creation of a silicon aluminide coating on IN738LC nickel-based superalloy has been investigated, using co-deposition process. Thermochemical calculations indicated the possibility of obtaining a silicon aluminide with NH4Cl activated pack powder at 900°C, in order to achieve coating with desirable structures. Two powder mixtures with nominal compositions of 7Si-14Al-(1-3) NH4Cl-Al2O3 (wt. %) and 16Si-4Al-(1-3) NH4Cl-Al2O3 (4 and 0.5 Si/Al ratios, respectively) were used. According to the results, both coatings showed multi-layered structures containing AlNi2Si as dominant phase. In coating created by pack powder with Si/Al ratio of 0.5, a porous and brittle layer of NiSi was formed on the surface which deteriorated the mechanical properties of coating to some extent. It was found that inward diffusion of Al was dominant at the first stage, while afterward, inward diffusion of Si led to conversion of NiAl phase to AlNi2Si and, finally, to NiSi phase. Eventually, the sample coated by Si/Al=4, showed superior microstructural characteristics, containing desirable AlNi2Si phase without undesirable brittle NiSi phase.
Mrs M. Akbari, Dr S. Sabooni, Dr M. H. Enayati, Dr F. Karimzadeh,
Volume 36, Issue 2 (9-2017)
Abstract
In the present study, FeAl/Al2O3 nanocomposite coating was produced on the carbon steel plate using mechanical alloying (MA) technique via a mechanochemical reaction. Stoichiometric ratios of Fe, Al and Fe2O3 as well as a substrate were mixed and milled up to 22h in a vibrating high energy mill with a 4 mm ball. Samples prepared after 18h of MA were subjected to annealing at 773 K for 1-3 h. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and microhardness measurements were carried out to study mechanochemical reaction and coating formation characterization. The results showed that mechanochemical reactions were started after 10h of MA, which finally caused the slight formation of FeAl/Al2O3 nanocomposite. Increasing the milling time to 18 hours led to the continuous increase of the coating thickness up to 80 μm, while the coating layer fractured and began to peel by further milling. The microhardness of the coating after 18h milling was 1050 vickers. Annealing of the 18h milled powders at 773K for 3h led to the complete formation and synthesis of the FeAl/Al2O3 nanocomposite. The results showed that the annealing treatment had considerable effects on the hardness increase up to 1200 vickers as well as adhesion strength of the composite coating.
S. Daneshvar E Asl, S. K. Sadrnezhaad,
Volume 36, Issue 3 (11-2017)
Abstract
TiO2/MWCNT nanocomposite thin films containing different percentages of multi-walled carbon nanotubes were coated on fluorinated tin oxide substrates by sol-gel dip coating method. Results of X-ray diffraction analysis indicated that the crystal structure of the coatings was anatase TiO2. It was also understood that the size of crystallites reduced with CNT but structural properties and equilibrium phase remain intact. Field emission scanning electron microscope images showed that CNTs dispersed uniformly among 45 nm spherical TiO2 particles of close relations. These images also showed that CNT promoted cracks on the coated surface. Results of the UV-Vis spectroscopy showed that the visible light range adsorption increased with CNT and the absorption edge did not significantly differ with the pure TiO2 layers.. Results of the photoluminescence spectroscopy revealed that the presence of CNT could reduce the pair electron–electron holes recombination which is considered totally undesirable.
H. Rashtchi, M. Shamanian, K. Raeissi,
Volume 36, Issue 4 (3-2018)
Abstract
Stainless steel bipolar plates are preferred choice for use in Proton Exchange Membrane Fuel Cells (PEMFCs). However, regarding the working temperature of 80 °C and corrosive and acidic environment of PEMFC, it is necessary to apply conductive protective coatings resistant to corrosion on metallic bipolar plate surfaces to enhance its chemical stability and performance. In the present study, by applying Ni-Mo and Ni-Mo-P alloy coatings via electroplating technique, corrosion resistance was improved, oxid layers formation on substrates which led to increased electrical conductivity of the surface was reduced and consequently bipolar plates fuction was enhanced. Evaluation tests included microstructural and phase characterizations for evaluating coating components; cyclic voltammetry test for electrochemical behavior investigations; wettability test for measuring hydrophobicity characterizations of the coatings surfaces; interfacial contact resistance measurements of the coatings for evaluating the composition of applied coatings; and polarization tests of fuel cells for evaluating bipolar plates function in working conditions. Finally, the results showed that the above-mentioned coatings considerably decreased the corrosion and electrical resistance of the stainless steel.
M. Falsafein, F. Ashrafizadeh,
Volume 37, Issue 2 (9-2018)
Abstract
Nitride coatings with excellent hardness and wear resistance have been deposited by physical vapor deposition (PVD) in recent years. For most applications, the load bearing and adhesion of coatings are very important and can determine the life and performance of the final components. In this study, CrN/CrAlN nanostructured coatings with different thicknesses and numberes of layers were deposited on the stainless steel AISI 420 and hot-work tool steel by cathodic arc evaporation. Nanoindentation, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) were used for the structural characterization and estimation of stress in the coatings. Adhesion of coatings was evaluated by scratch adhesion and VDI 3198 Rockwell tests. The results revealed the high values of compressive residual stress in the physical vapor deposited coatings, in the range of 500 to 1800 MPa, with a detrimental effect on coating adhesion. Load bearing capacity was observed to be dependent on the thickness and adhesion of coating, reaching the maximum at an optimum thickness. Overall, the results proved that the type of steel substrate could have a significant influence on the coating adhesion.
M. Alizadeh, A. Cheshmpish,
Volume 37, Issue 2 (9-2018)
Abstract
In this research, Ni-Mo-Al2O3 composite coatings were electro-deposited on the mild carbon steel in a citrate bath containing micro- sized Al2O3 particles. Afterward, the effect of the particle concentration in the electrolyte bath (ranging from 0 g/L to 30 g/L) on the microstructure, microhardness, and corrosion performance was evaluated. To investigate the microstructural changes and the surface morphology of the coatings, as well as the particle distribution in the deposits, optical and scanning electron microscopy coupled with the energy dispersive X-ray spectroscopy was utilized. The corrosion behavior of the prepared coatings was investigated in a 3.5 wt. % NaCl solution. The results showed that the presence of the Al2O3 particles in the Ni-Mo coatings changed the microstructure and also, increased the microhardness and corrosion resistance of them. It was also found that the desirable structure of the protruding crystallite morphology with no detectable pores could be achieved at the medium concentrations of reinforcement (e.g. 20 g/L). Further the optimum concentration of the particles in the electrolyte bath to attain the composite coating with the desirable microstructure and consequently, the desirable corrosion resistance was found to be 20 g/L.
