Showing 34 results for Coating
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.
Sh. Tavakoli Dehaghi, S. Darvishi, Sh. Nemati, M. Kharaziha,
Volume 37, Issue 3 (12-2018)
Abstract
Abstract: With the advances in the development of biomaterials for tissue replacement, the attention of scientists has been focused on the improvement of clinical implant properties. In this regard, despite the appropriate properties of the stainless steel, the application of stainless steel as implants has been limited due to the weak corrosion resistivity. The purpose of this paper was preparation and characterization of hydrophobic polydimethylsiloxane (PDMS)-SiO2-CuO nanocomposite coating on the 316L stainless steel surface. The 316L stainless steel was coated by SiO2 nanoparticles (20 wt. %), CuO nanoparticles (0.5, 1 and 2 wt. %) and biocompatible PDMS. In this research, x-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied to characterize the coating. Moreover, the roughness and water contact angle of the coatings consisting of various amounts of CuO nanopowder were estimated. Finally, the effects of various amounts of the CuO nanopowder on the corrosion resistivity of nanocomposite coatings were investigated. XRD patterns confirmed the presence of crystalline CuO nanoparticles on the substrate. Due to the non-crystalline nature of silica nanoparticles and the semi-crystalline PDMS polymer, no peak confirming the presence of these phases was detected on the XRD pattern of the nanocomposite coating. SEM images showed the formation of a lotus leaf-like layer on the surface of the nanocomposite coating containing 1 and 2 wt. % CuO. Moreover, water contact angle evolution revealed that while contact angle was 81 degree without CuO nanoparticles, it was enhanced to 146 degree in the presence of 1 wt. % CuO. Moreover, the corrosion study showed the nanocomposite containing 2 wt.% CuO had the best corrosion resistance, the corrosion current density of 2.1E-7 A.cm-2, and the corrosion potential of 0.22 V.
M. Akbarzadeh, M. Zandrahimi, E. Moradpour,
Volume 37, Issue 4 (3-2019)
Abstract
Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants. In this study, MoS2-Cr composite coatings were deposited onto AISI 1045 steel substrates by direct-current magnetron sputtering. The MoS2/Cr ratio in the coatings was controlled by sputtering the composite targets. The coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and nano-indentation and nano-scratch techniques. The tribological behavior of the coatings was investigated using the pin-on-disc test at room temperature. The results showed that the thickness and the hardness of the coating were 6 µmand 850-1300 HV, respectively. The degree of the crystallization of the composite coatings was enhanced with increasing the Cr contents. The incorporation of Cr into MoSx coatings resulted in the considerable improvement of coating adhesion and hardness. The optimum doping level for MoS2-Cr coatings to show the best tribological propertie was 13 atomic percent. The main wear mechanisms of the coating were delamination, tribochemical and abrasive micro cracking
M. Barjesteh, K. Zangeneh Madar, S. M. Abbasi, K. Shirvani,
Volume 38, Issue 2 (9-2019)
Abstract
In this study, the effect of platinum-aluminide coating parameters on surface roughness of nickel-based superalloy Rene®80 was evaluated. For this purpose, different thicknesses of Pt-layer (2, 4, 6 and 8µm) were plated on the Samples. Then diffusion aluminide coating in two types, high tempeature-low activity and low temperature-high activity was performed. The results of structural investigations by scanning electron microscope and X-Ray diffraction indicated a three-zone structure of coating in all thicknesses of platinum layer, as well as in the two methods of aluminizing. Surface roughness of coatings was measured in three steps: 1-after Pt plating, 2-after Pt diffusion, and 3-after aluminizing and final aging. The results showed that the thickness of Pt and the final thickness of the coating directly affected the surface roughness. The minimum surface roughness was created by high temperature low activity with 2µ of Pt-layer (2.6μm) and the maximum of surface roughness was obtained in low-temperature high activity with 8µ of the Pt-layer (8.8 μm).
F. Shahriari Nogorani, M. Afari, M. A. Taghipoor, A. Atefi,
Volume 39, Issue 1 (5-2020)
Abstract
Practical applications of thermal barrier coatings with aluminide bond-coats are limited due to oxide scale spallation of the aluminide coating under applied thermal stresses. Considering the positive effects of oxygen-active elements or their oxides on the high temperature oxidation behavior, in this research zirconia was introduced into an aluminide coating. For this purpose, a Watts type bath was used to electroplate a layer of Ni-ZrO2 composite on a Ni-based substrate. Aluminizing was performed using the conventional two-step process at 760 and 1080 °C. Microstructural characterization of coatings in the as-coated conditions and after cyclic oxidation via 5-hour cycles at 1050 °C was performed using electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The results showed that the general three-zone microstructure of the simple high activity aluminide coatings develops below the pre-deposited nickel-zirconia layer and latter converts to a nearly un-alloyed porous NiAl. In spite of its porous surface layer, the zirconia modified coating has a higher oxidation resistance than the unmodified aluminide coating.
N. Bahremandi Tolou, H. R. Salimi Jazi, M. Kharaziha, N. Lisi, G. Faggio, A. Tamburrano,
Volume 39, Issue 1 (5-2020)
Abstract
In recent years, graphene has been considered in various tissue engineering applications such as nerve guide conduits because of its unique properties such as high electrical and mechanical properties, porous structure for exchange of nutritious and waste materials, biocompatible, capability of drug and growth factor delivery. In the current study, nerve guide conduits based on a 3D graphene were synthesized by induction heating chemical vapor deposition (ICVD). Graphene was synthesized on Ni foam template at 1080 ͦC. Fabricated samples were characterized by Raman analysis and Scanning Electron Microscopy. Raman analysis showed that the synthesized graphene is in the form of a turbostratic multilayered graphene with little defects. Cyclododecane (CD) as a temporary protective layer was used to remove nickel. After removing nickel, the free-standing 3D-graphene structure was coated with a polymer (PCL) by drop and dip coating methods to obtain the composite conduit. A comparison of the electromechanical results of the 3D-graphene/PCL conduit and PCL conduit indicated that firstly, grapheme increased the electrical conductivity of the composite conduit which will help promote nerve regeneration and axon growth. Secondly, tensile strength and flexibility of the 3D-graphene/PCL conduit was improved compared to the PCL conduit.
M. Toorani Farani,
Volume 39, Issue 1 (5-2020)
Abstract
In this study, Plasma Electrolytic Oxidation (PEO) at three frequencies of 500, 1000 and 3000 Hz was applied on Mg surface and the effect of PEO surface preparation on protective behavior of three types of epoxy, fusion bond epoxy (FBE) and polyurethane coatings was investigated. The microstructural and protective properties of PEO coatings were studied by SEM, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the coating formed at frequency of 3000 Hz had smaller pore size and better protection properties. EIS test in 3.5 Wt.% NaCl solution was also used to investigate the protective behavior of the two-layered coatings. The results showed that PEO process had a favorable effect on the protective behavior of the polymer layers. Moreover, the best protection behavior was related to the PEO/FBE coating system.
S. Arjmand, M. Tavoosi,
Volume 39, Issue 3 (12-2020)
Abstract
The present work aims to modify surface properties of pure Ti by development of Ti-Al-N intermetallic composite coatings. In this regard, tungsten inert gas (TIG) cladding process was carried out using Al 1100 as filler rod with Ar and Ar+N2 as shielding gases. Phase and structure of the samples were investigated by X-ray diffraction (XRD) technique, optical microscopy (OM) and scanning electron microscopy (SEM). Hardness values and corrosion behavior of the obtained coatings were also compared using Vickers microhardness tester and potentiostat, respectively. The results showed that composite structure containing Al3Ti, Ti3Al2N2 and Ti3Al intermetallic compounds could be formed on the surface of pure Ti. Amounts of brittle phases and welding defects at the titanium-coating interface were least by welding under pure Ar shielding. Despite the increasing amount of structural defects such as porosity and non-uniformity under Ar+N2 shielding, the prepared coatings had higher hardness (more than 100 HV) and corrosion resistance (more than twice) compared with those obtained under Ar shielding.
A. Zamani, M. R. Loghman Estraki, S. R. Hosseini, M. Ramezani, A. Al-Haji,
Volume 39, Issue 3 (12-2020)
Abstract
The aim of the study was to investigate the effect of temperature, time, pH, capping agent concentration (mercaptoacetic acid), Zn to Se and Se to reducing agent (NaBH4) mole ratios on morphology, phase developments and size of zinc selenide nanoparticles prepared by hydrothermal method. Characterization of zinc selenide nanoparticles was performed by Field Emission Electron Microscopy (FESEM), Energy Dispersive X-ray Spectrometry (EDS), X-ray Diffraction (XRD), Induced Coupled Plasma Spectrometry (ICP), Fourier Transform Infrared spectroscopy (FTIR) and Simultaneous Thermal Analysis (STA). The results of EDS showed that the ratio of atomic percentage of Zn to Se in the optimized zinc selenide nanoparticles is 1: 1 and elements are evenly distributed in the nanoparticles. Based on the results of FTIR and STA thermal analyses, MAA as the stabilizing agent binds to and stabilizes zinc selenide nanoparticles. Finally, fine nanoparticles of zinc selenide with narrow size distribution, spherical shape and cubic crystal structure were obtained at the minimum temperature (130 °C) and processing time (15 hours) with the least amount of reducing and capping agents compared to previous researches.
S. N. Hosseini, F. Karimzadeh, M. H. Enayati,
Volume 39, Issue 4 (2-2021)
Abstract
The bare and pre-oxidized AISI 430 pieces were screen printed by copper ferrite spinel coatings. Good bonding between the coating and the substrate was achieved by the reactive sintering process of the reduced coating. The energy dispersive X-ray spectroscopy (EDS) analysis revealed that the scale is a double layer consisting of a chromia-rich subscale and an outer Cu/Fe-rich spinel. The results showed that the spinel protection layer not only significantly decreased the area specific resistance (ASR), but also inhibited the subscale growth by acting as a barrier to the inward diffusion of oxygen. ASRs of 19.7 and 32.5 mΩ.cm2, much lower than that of the bare substrate (153.4 mΩ.cm2), at 800 °C after 400 h oxidation were achieved for the bare and pre-oxidized copper ferrite spinel coated samples, respectively. Excellent, stable ASR (20.5 mΩ.cm2) was obtained with copper ferrite coating after 600 h of exposure at 800 °C. The high electrical conductivity of CuFe2O4 and its doping by Mn, the growth reduction of Cr2O3 oxide scale and the good coating to substrate adherence are proposed to be responsible for substantial improvement in electrical conductivity.
S. Arjmand, G. H. Akbari, G. R. Khayati,
Volume 39, Issue 4 (2-2021)
Abstract
The purpose of the present work is to investigate the influence of the number of weld-passes on microstructure, hardness and residual stresses of composite coatings composed of Ti-Al-Si intermetallic compounds. In this regard, surface coating of pure Ti was carried out using one and two passes of tungsten inert gas (TIG) welding with an Al filler alloy (grade 4043). Phase and structural evaluations of the coatings were investigated by X-ray diffraction, optical and scanning electron microscopies. microhardness and residual stress values of the coatings were measured using ASTM E384-HV device and the Sin2ψ method, respectively. The results showed that as the number of welding passes increased or the dilution ratio decreased, the volume fraction of Ti5Si3-Al3Ti intermetallic phases within the fusion zone increased and the volume fraction of martensite phase in the heat affected zone decreased. As a result, the average hardness value of the coating increased to be about 130 % compared to that of the pure Ti substrate. The tensile residual stresses at the center line of fusion zone were 165 ± 30 and 210 ± 35 MPa for the coatings prepared in one and two welding passes, respectively.
S. Borhani Esfahani, H. R. Salimi Jazi, M. H. Fathi, A. Ershad Langroudi, M. Khoshnam,
Volume 40, Issue 1 (5-2021)
Abstract
In this research, a kind of environmentally-friendly inorganic-organic hybrid nanocomposite coating based on silica containing titania/silica core/shell nanoparticles was synthesized and characterized for conservation of facade tiles in historical buildings. The matrix of the composite was prepared by sol-gel process via two methods of ultrasonic and reflux stirring. Tetraethyl orthosilicate (TEOS) and poly-dimethyl siloxane hydroxy-terminated (PDMS-OH) were used for the formation of silica network and creation of flexibility and hydrophobicity, respectively. Titania nanoparticles were used in the form of titania/silica core/shell as ultraviolet absorber. The synthesized nanocomposite was applied on the microscope slides and tiles by dip coating technique. The properties of nanoparticles and coatings were characterized by Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and water contact angle measurement. The results revealed that formation of titania/silica core/shell structure was successful. The investigation of PDMS content effect on transparency, cohesion and hydrophobicity of the coating confirmed that the optimum content of this siloxane was around 20 wt.%. In general, the results showed that the silica-based hybrid nanocomposite reinforced with TiO2/SiO2 core/shell nanoparticles could produce a transparent and hydrophobic coating for tile and glass protection.
P. Verdi, S. M. Monirvaghefi, F. Ashrafizadeh,
Volume 40, Issue 3 (11-2021)
Abstract
Regarding to the low rate of conventional Ni-P electroless plating method that needs more time to make a coating on the substrate surface, a new technique called “substrate local heating” was introduced based on the temperature parameter modification and its advantages were expressed and compared to the conventional electroless plating technique (temperature=90°C, pH=4.7). In order to provide necessary equipment making this approach practicable, electrical resistance was used as the heating source, and air injection and cooling water circulation were employed to control the solution temperature near the substrate and in the bulk solution, respectively. Considering the heater power (1000 W), the substrate and bulk temperatures were about 190°C and 80°C, respectively. This novel method could enhance the plating rate up to 32 µm/h which was about 60% greater than that of the conventional method, 20 µm/h. Moreover, benefits such as local plating, reduction of production costs, and formation of functionally graded coatings (FGC) can be achieved.
O. Ganji, S.a. Sajjadi, M. Mirjalili, Z.g. Yang,
Volume 40, Issue 4 (3-2022)
Abstract
Carbide coatings, due to their excellent anti-wear properties, are used to extend the life of molds exposed to abrasion forces. Various processes have been applied to produce carbide coatings. Thermo-reaction diffusion (TRD) using a molten salt bath could be considered as an economical method compared to other coating processes. In this study carbide-composite coatings using molten salt baths composed of oxides of carbide forming elements (chromium and vanadium) on SKD-11 and T10 tool steels at 1000 ℃ were formed. The results showed that the coatings included chromium carbide phases: CrC, Cr7C3, and Cr23C6 as well as vanadium carbide: VC, VC0.88, V6C5, V8C7, and a triple phase with the composition of Cr2C2V. The highest hardness (1890-2020 HV) and the lowest coefficient of friction (0.14) were achieved by the carbide coating of T10 steel with the second bath of vanadium oxide.
Sh. Talebniya, M. R. Saeri, I. Sharifi, A. Doostmohammadi,
Volume 41, Issue 1 (8-2022)
Abstract
Magnetic nanoparticles are of interest in various research fields such as magnetic fluids, catalysts, biotechnology, medicine, information storage, and environmental issues. However, spinel ferrite magnetic nanoparticles with proper magnetic properties could not be used alone in these applications because of their lack of biocompatibility and instability in aqueous solutions. Surface coating is an effective strategy to eliminate or minimize this issue. In this study, FeFe2O4 and ZnFe2O4 spinel ferrites were synthesized using the reverse co-precipitation method under a nitrogen gas atmosphere. The magnetic behavior of the particles, determined by a vibrating magnetometer (VSM) showed the saturation magnet (Ms) values of the FeFe2O4 and ZnFe2O4 spinel. Fourier-transform infrared (FTIR) spectra showed two high-frequency bands v1 and v2 at about 554-578 and 368-397 cm-1, respectively, which were related to the spinel structure. Finally, the synthesized FeFe2O4 nanoparticles were coated with chitosan and polyethylene glycol (PEG) biopolymers. The TEM and FTIR analysis indicated that the magnetic nanoparticles were uniformly coated by the biopolymers.
