جستجوی مقالات مرتبط با کلیدواژه « مقاومت به خوردگی » در نشریات گروه « مواد و متالورژی »

Magnesium and its alloys are very suitable for making implants in physiological environments such as the human body from the point of view of being biodegradable, and they also have a hardness close to the bone. In addition, the characteristics of magnesium include lightweight, high strength, and good biocompatibility, which has created a tremendous change in the field of medicine for the new generation of biomaterials. However, magnesium alloys are associated with high degradation due to the release of hydrogen gas and the improvement of the surrounding tissues. Magnesium implants lose their mechanical integrity during the healing period before the bone heals due to the high degradation process. Various methods and techniques have been proposed to control the amount of magnesium degradation to acceptable levels. This article discusses an overview of the types of conversion coatings, effective methods to increase the quality of these coatings, and the factors affecting the performance of conversion coatings in improving the corrosion resistance of magnesium alloys. Among the different approaches, chemical conversion coatings are the most simple and cost-effective method, which even can remove the weak points of components with complex designs such as implants and stents. The conversion coatings are uniform and very sticky, and the expected characteristics of the coating can be obtained easily by changing the temperature, pH of the bath, and other compelling features. In this research, the types of conversion coatings and the strengths and weaknesses of each of these coatings have been investigated.

The aim of this research is to improve the corrosion resistance and create the active inhibitory in hybrid-silane coatings. Therefor the graphene oxide (GO) nano-sheets and the methylene triphosphonic acid (ATMP) were used as a protective pigment and organic inhibitor carrier in the coating, respectively. The peaks appearing in 1059, 1380, 1730, and 3430 cm-1 belong to hydroxyl stretching, carbonyl, hydroxyl bending, and epoxide groups confirmed the successful synthesis of GO nanoparticles by infrared transfer spectroscopy (FTIR). The displacement of two peaks of 230 and 250 nm in GO to 261 and 360 nm in GO-ATMP represent the successful reduction of graphene oxide by ATMP molecules. Then, the corrosion resistance of GO-ATMP coating was evaluated using electrochemical impedance spectroscopy (EIS) and polarization tests. The results showed that the ATMP inhibitor improves the corrosion resistance properties of the coating, and the corrosion current density is reduced as 50%. After successfully inhibiting adsorption on GO plates, the coating (GO-ATMP) was applied on 2024 aluminum alloy sheets. The results of EIS and salt-spray tests showed that the corrosion resistance properties of GO-ATMP coatings improved due to restrict the access of corrosive environment to the metal surface. The intelligent releasing of the inhibitor during electrolyte penetration in scratched area of the coating was confirmed by the formation of a protective film in the scratch area in the electron microscope image of the sample. This caused to restrict the electrochemical reactions.

In this research, superhydrophobic nickel and cobalt coatings with a hierarchical micro-nano structure were deposited on copper substrate by rapid one-step electrodeposition. The microstructure, wettability, corrosion resistance, self-cleaning and anti-icing properties of the coatings were evaluated using a scanning electron microscope (SEM), contact angle measurement, electrochemical impedance spectroscopy (EIS), alumina powder as contaminants and keeping at minus 15 °C, respectively. According to the obtained results, nickel coating with a higher contact angle of 172.3° delays the freezing of the droplet on the surface by 6 min more than the cobalt coating with a lower contact angle of 155.6°. The surface energies of both coatings were low enough to benefit from oleophobicity and for glycerol and ethylene glycol, both coatings had water contact angles higher than 120°. When the open circuit potentials were atablized in 3.5 wt.% NaCl solution, very high charge transfer resistances of 2370 and 756.3 kΩ.cm2 were recorded for nickel and cobalt coatings, respectively. After 16 days of immersion in saline solution, the contact angles were still in the hydrophobic range (128.7° and 98.6° for nickel and cobalt coatings, respectively). For cobalt coating with more appropriate surface microstructure and despite its lower water contact angle compared to nickel coating, better self-cleaning properties were observed.

The purpose of this study is to use of an Eco-friendly accelerator in zinc-calcium phosphating process. For this, the conventional phosphating parameters (containing nitrate and nitrite) were optimized using literature; Then, the accelerators were substituted with H2O2. The morphology of the phosphate coatings was observed by a scanning electron microscope (SEM), and the chemical compositions were investigated by energy dispersive X-ray spectroscopy (EDS). The crystalline structures of the phosphate coatings were analyzed by X-Ray Diffraction (XRD). The corrosion resistance of samples was assessed through polarization tests in 3.5 wt.% NaCl solution. According to the results, about 0.6 mL/L was obtained as optimum concentration of H2O2. Also, the optimum temperature and pH of phosphating were about 47 °C and 3.2 respectively. The XRD results indicated that the coating structure include phosphophyllite, hopeite and some scholzite phases. SEM images showed that, in the presence of H2O2, the geometrical shape of coating crystals is cubic, which are grown uniformly on the entire area the substrate. Also, according to the electrochemical parameters, the coating obtained from the bath containing 0.6 mL/L of H2O2, has the highest corrosion resistance. Therefore, it can be deduced that, H2O2 could be used to replace the traditional accelerators like nitrate and nitrite, since it is less pollutant and provides better quality of the coating.

Chromate conversion coatings with anti-corrosion properties are used as coatings for external elements of space systems. The three main properties of these coatings that are effective in aerospace application are: corrosion resistance, adhesion strength of the coating to the substrate and abrasion resistance. In this paper, the parameters affecting these properties were investigated and in order to optimize these parameters, the response surface methodology (RSM) method was used in MiniTab program. Variable parameters are temperature, amount of refiner and amount of accelerator. The amount of constituent material, reaction time and age time were considered constant for all samples. The corrosion resistance, adhesion strength of the coating to the substrate and abrasion resistance are determined by salt spray test in 0.5% saline medium for 336 hours, Pull Off test and pin on disk wear test, respectively. The maximum amount of corrosion resistance obtained for chromate coating which was 71.8% of the surface remind intact, with the combination of 4 g/lit refiner, 1.8 g/lit accelerator at 45 °C. The maximum amount of coating stress from the substrate surface was 1.2 MPa, which was obtained in the amount of 4 g/lit refiner, 1.8 g/lit accelerator and 35 °C temperature. The minimum weight loss due to abrasion was 0.2 mg, which was obtained for coating with the composition 4 g/lit refiner, 6 g/lit accelerator at 35 °C. Therefore, by increasing the amount of accelerator and temperature, the thickness of the coating increased, and this increase to the optimum level increases the abrasion resistance and adhesion strength of the coating, but when the thickness increases beyond the optimum, the abrasion resistance and adhesion strength decrease.

mproving corrosion resistance is one of the main goals of orthopedic implants. In this regard, this study aims to improve the quality and efficiency of the AZ31 M agnesium alloy by phosphate coatings containing hydroxyapatite and ZnO nanoparticles by M AO method. For this purpose, first, the effect of adding hydroxyapatite nanoparticles in constant current mode was investigated and then the effective parameters in this method, including time and duty cycle, were studied. Corrosion behavior of the coatings was investigated in Ringer's solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). M icrostructural and phase studies of coatings by field emission scanning electron microscopy (FESEM /EDS) and X-ray diffraction (XRD) analysis before and after corrosion test showed better performance of the coating produced in the electrolyte containing 3 grams per liter of hydroxyapatite nanoparticles in 7 minutes and 50% duty cycle.

The study of superfluid levels due to the importance of these levels in many applications has been considered. In this study, nickel-copper alloy coatings were created using a two-step electrochemical deposition method-the surface energy reduction and microstructure and corrosion resistance were investigated. Surface morphology was investigated using scanning electron microscopy and XRD for field publishing and fuzzy structure. Corrosion resistance was investigated using potentiodynamic polarization method as well as electrochemical impedance spectroscopy. The results of this study showed that by increasing the concentration of Modidium crystal in the coating bath, the nanostructured coating was obtained and at a concentration of 200 grams per liter, a hieratic hierarchy coating was obtained. XRD data showed that only the nickel phase was created and a solid solution was created by the entry of copper atoms into the structure. Corrosion behavior studies showed that with the formation of coating, the corrosion density decreased from 6.2 to 0.12 mA/cm2 , and corrosion potential from-273 to -171 also decreased. The reason for this was the capture of trapped air in the coating, thereby preventing the entry of corrosive ions into the substrate as well as the Laplace pressure.

An imidazoline based inhibitor was synthesized using oleic acid and diethylenetriamine (DETA). The characteristic properties of the synthesized inhibitor were investigated by FTIR and HNMR tests. Tafel polarization technique and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical and corrosion inhibition properties of the inhibitor in CO2 saturated 3% NaCl solution. Potassium iodide was added to the corrosion media to enhance the inhibition efficiency of the inhibitor. The measured corrosion rates were optimized by Design Expert 10.0.7 software using central composite design and response surface method. Temperature and inhibitor concentration were selected as the most effective parameters. Analyses of variance (ANOVA) were performed on the results of the designed experiments. It was found that temperature and inhibitor concentration effects on corrosion rate and inhibition efficiency are complicated and their interactions. Addition of KI to the inhibitor system had a synergistic effect on the corrosion inhibition. It almost eliminated the dependency of the corrosion rate to temperature and inhibitor concentration which is a great achievement in inhibitor applications in oil and gas industries. DOE data revealed that the best inhibition of corrosion occurred at 25oC with 37.7ppm of synthesized Imidazoline inhibitor and 2000ppm KI. It is estimated by the software that at this point the corrosion rate is 6µm/year and polarization resistance is 30788Ω. The synthesized inhibitor conforms perfectly to the Langmuir adsorption isotherm.

Transient liquid phase (TLP) bonding of AISI 304L stainless steel was carried out using BNi-2 amorphous interlayer. The microstructure of the joint area was studied by using optical and scanning electron microscopes and energy dispersive spectroscopy. The effect of bonding temperature (1030-1110 °C) was studied on the microstructure and corrosion behavior of the TLP bonded samples. Electrochemical corrosion resistance of the bonded samples was evaluated in 3.5% NaCl solution at room temperature. The mechanism of the microstructure formation and the solidification sequence at the joint area were discussed. Ni- and Cr-rich borides, Ni-Si-B compound and fine Ni3Si particles were identified in the γ-Ni matrix at the joint centerline. The microstructural investigations revealed that the solidification sequence of these phases is: L→ γ + L → γ + Ni boride + Cr boride + L → γ + Ni boride + Cr boride + Ni-Si-B Compound. The highest corrosion resistance was observed in the sample bonded at 1070 °C for 30 min, which is comparable to that of the as-received AISI 304L stainless steel. It was attributed to the bond region microstructure with a negligible amount of eutectic constituents formed in the athermally solidified zone.

In this research, the effect of current intensity on the corrosion resistance of Ti-6Al-4V alloy welded by Tungsten-inert Gas (TIG) method was investigated. For this purpose, 3 × 50 × 40 mm specimens were prepared and after preparing the surfaces, in a way but joint two-way single pass in vacuum chamber with inert argon with a flow rate of 70, 80 and 90 A were welded. Microstructural studies of base metal (BM), fusion zone (FZ) and heat affected zone (HAZ) were performed using optical microscopy and scanning electron microscopy (SEM). Then, in order to investigate the corrosion resistance of Ti-6Al-4V welded cross sections, the roots of the welded specimens were examined by potentiostatic polarization in seawater and 3.5% NaCl. The results showed that by increasing the welding current intensity from 70 to 80A, the grain size in the weld area as well as the corrosion rate of the weld area in Ti-6Al-4V alloy increased. By varying the flow intensity from 80 to 90A, the corrosion rate and grain size of the weld zone did not change significantly. The corrosion rate of Ti-6Al-4V alloy in 3.5% NaCl solution compared to seawater revealed that the corrosion rate of alloy in 3.5% NaCl solution is higher than its corrosion rate in seawater.

According to the widespread use of aluminum alloys in the oil and gas and petrochemical industries and their low corrosion resistance in corrosive environments, it is necessary to make the surface of these alloys resistant to corrosion using a appropriate coating method. In this research, the coating method in an aqueous environment in an autoclave on the surface of 6061 aluminum alloy was used and its corrosion resistance was investigated. The cleaned samples were placed in an autoclave. Then, by controlling the temperature, time and pressure, an oxide / hydroxide coating was created on the surface. X-ray diffraction (XRD) patterns showed that the coating generally contained an AlO(OH) phase. Scanning electron microscopy (SEM ) images of the coating surface showed that the cubic nanocrystals were densely formed throughout the surface. Vickers microhardness test also showed that the coating was soft and had no effect on the surface hardness. However, the polarization curves show that the corrosion current density of the generated substrates is significantly reduced and the corrosion potential is more positive. As the parameters of autoclave temperature, time and pressure increase, the coating thickness increases and the corrosion current density decreases. It was also concluded that the coating method in the aqueous environment inside the autoclave in liquid and immersed state is a more desirable method due to the higher autoclave pressure than the water vapor state. This indicates that the corrosion resistance of 6061 aluminum alloy has been significantly increased by the use of steam coating.

Quench-Polish-Quench(QPQ) is a low temperature process in a liquid salt bath and is used for modifying the surfaces of metals to enhance corrosion and wear resistance. In this research, the effects of the compound and oxide layers on microstructure and corrosion properties of steel CK67 were investigated. The QPQ process was carried out by nitriding at 580°C for 120 minutes, followed by the oxidation treatment at 380°C for 20 minutes. The modified surface was then studied by using optical microscopy (OM ), scanning electron microscopy (SEM ), X -ray diffractometer (XRD), corrosion and microhardness tests. The results show that the surface layer consists of Gamma prime (γ'), iron, magnetite, and epsilon nitride(Ɛ ). Accordingly, the nitriding and the following oxidation treatment led to the enhanced corrosion properties and hardness in comparison to the steel before applying the QPQ process. The most achieved value of hardness was 587 HV which was nearly three times higher than that without the QPQ process. In addition, after 144-hour salt spray testing, corrosion products were observed on the coated surface.

In this research, the influence of H321 stabilizing heat treatment on microstructure, hardness, and intergranular corrosion resistance of 1cm thick sheet of AA5083 has been investigated. After 10%, 20%, 30%, and 40% cold rolling of samples, they were all annealed for recrystallization. The processes of rolling and annealing have been repeated until 1.5mm thickness samples were obtained. Then, 30% cold work was applied to them to achieve sheets having 1mm thickness. For stabilizing treatment, samples were put in the heat treatment furnace for 1 and 4 hours in a temperature range of 150°C to 300°C. Then, sensitization treatment was applied to the samples at 150°C for 48h to consider the effect of stabilizing. The results show that the hardness of samples decreases by increasing stabilizing temperature. The optimum stabilizing temperature for samples with 10% to 30% rolling is 220°C to attain the highest corrosion resistance, but this treatment does not improve the sample's corrosion resistance with 40% rolling. In conclusion, the sample with 20% rolling, which stabilized at 220°C, exhibits mass loss of 6 to 9 mg/cm2 and hardness of 100HV in 4h and 110HV in 1h of stabilizing time has the optimum combination of hardness and intergranular corrosion resistance.

In this study, soft PTFE particles and hard Si3N4 nanoparticles were simultaneously introduced into the Ni-B electroless coating and the Ni-B-PTFE-Si3N4 nanocomposite coating was prepared on plain carbon steel. The microstructure and morphology of the coatings were examined by scanning electron microscopy, and the corrosion resistance was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that by introducing PTFE particles into the coating bath, Ni-B-PTFE composite coating was successfully prepared. The best corrosion resistance of Ni-B-PTFE coating was achieved when a concentration of 3 g/L PTFE particles were used. The corrosion current density was 2.3 μA/cm2. However, introduction of Si3N4 nanoparticles into the Ni-B coating can also improve the corrosion resistance of the coating. The best corrosion resistance of Ni-B-Si3N4 coating was obtained at a concentration of 4 g/L Si3N4 nanoparticles, with a corrosion current density of 2.2 μA/cm2. Simultaneous application of hard and soft particles in the coating increased corrosion resistance, and the corrosion current density was 0.76 μA/cm2 for Ni-B-PTFE-Si3N4 coating. The results of hardness and abrasion tests showed that the addition of Si3N4 nanoparticles leads to an increase in the hardness and friction coefficient of Ni-B coating from 847 Vickers and 0.6 to 963 Vickers and 0.78, respectively. Nevertheless, the incorporation of PTFE particles reduces the hardness and coefficient of friction to 572 Vickers and 0.35, respectively. Simultaneous application of hard and soft particles resulted a hardness of 871 Vickers and friction coefficient of 0.6.

Composite coatings containing P and ceramic particles are considered in terms of properties such as corrosion resistance, oxidation resistance and high hardness. In this study, Co-P-nanoAl2O3 composite coating was fabricated on the AISI 430 stainless steel substrate using a direct current electric deposition technique. The quality of the coating and its corrosion resistance were studied by changing the amount of alumina (3, 4, 5 and 6 g/L) in the electrolyte bath. In order to investigate the morphology of the composite coating and the analysis of the Co-P-nanoAl2O3 composite coated samples, a scanning electron microscope (SEM) and EDS analyzer were used, respectively. The results showed that by increasing the concentration of nano-alumina particles in the electrolytic solution from 3 g/L with a 1 unit increase to 5 g/L, the weight of nano-alumina particles in the coating increased. Then by increasing the concentration of nano-alumina particles in the electroplating solution the weight percentage of nano-alumina particles in the coating reduced. Also the results showed that, the composite coating formed in the bath containing 5 g/L alumina is perfectly uniform and continuous, while with increasing amount of alumina, it is not possible to form a suitable coating on the entire surface of the substrate. In order to investigate the corrosion resistance, potentiodynamic polarization experiments were applied in aqueous solution of 3.5% NaCl on coated and non-coated samples. The results of Tafel and electrochemical polarization tests were also correlated with microscopic images and showed that the coated in the bath containing 5 g/L alumina had the highest corrosion resistance.

In this research, Cu-Al2O3 composite tubes were fabricated by electroforming method using a rotating stainless steel rod as cathode and Cu-P alloy as anode. The microstructure, surface morphology, and the effect of alumina second phases on corrosion resistance of the fabricated tubes were investigated by the means of SEM images, X-ray diffraction, and corrosion tests, respectively. X-ray diffraction pattern proved the existence of alumina particles in the copper matrix of the fabricated tubes and also proved that no chemical reaction occurred between these two phases. SEM images indicated that the amount of alumina particles in the copper matrix is a function of its concentration in the electroforming bath, so that it would be maximum when 15 g alumina per liter was used, in the condition of the present study. The results of potentiodynamic polarization test carried out in 3.5 wt. % NaCl solution illustrated that corrosion potential and corrosion current density changed to positive and negative values, respectively, and corrosion rate decrease at all by increasing the amount of alumina particles in copper matrix of the tubes. Electrochemical impedance analysis also proved that corrosion resistance increase due to the presence of alumina in copper matrix.

Metal implants are widely used in medical and dental areas due to their good mechanical properties. The use of these metal implants in the corrosive environment of the body involves many problems, including the problems of corrosion-induced products that cause infection and cause the type of implants in the body to not function properly. In this research, sol-gel method was used to apply the hydroxyapatite / titanium dioxide coating on 316 Stainless Steel Alloy. All samples were coated with optimum conditions at 10 cm / min and pH =7, and then the corrosion resistance of the coatings was investigated in a ringer solution using potentiodynamic polarization and EIS methods. The composition of the coatings is also analyzed by XRD, EDX, FTIR. The morphology of the coating is determined by the scanning electron microscope (SEM). The results of the study showed that HA and TiO2 coatings and HA / TiO2 nanocomposite with 75, 50, 25% TiO2 coatings on a uniform thickness of 316 steel substrate. The results of the FESEM images showed that hydroxyapatite and titanium dioxide on the steel alloy 316 has uniform coverage and denser, and also by increasing the percentage of titanium dioxide nano hydroxyapatite / titanium dioxide from% 25 to% 50 It then becomes 75% nano-particles smaller and the coating becomes dense. Corrosion tests showed that the corrosion resistance of 316 Stainless Steel Alloy coated with nano HA / TiO2 by increasing the amount of TiO2 in the coating increases

One of the important parameters to increase the corrosion resistance of base metal is the selection of an appropriate primer. This is an important factor for increasing the adhesion and durability of the coating. In this study, the effect of two different primers on the corrosion resistance of the painted low carbon steel has been investigated. For this purpose, zinc phosphate (which is normally used as a paint primer) and Ni-P nano-structured coating were used. The corrosion resistance was evaluated by potentiodynamic and cyclic polarization tests, electrochemical impedance spectroscopy and salt spray tests. The Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used to characterize the morphology and composition of the coatings. And adhesion of the paint was investigated by pull off test. The results showed that the corrosion resistance of the painted low carbon steel with Ni-P nano-structured primer was more than that of the zinc phosphate primer. So that the polarization resistance increased by about 79.1 kΩ.cm2 and the pitting potential increased to 0.49V for nano-structured coating samples compared to zinc phosphate samples. Also, the results of the paint adhesion test indicated a high adhesion to nano-nickel-phosphorus primer compared to the phosphate-zinc primer.

In this research, titanium carbo-nitride coatings were synthesized on the surface of Ti-6Al-4V alloy by nitro-carburizing route and the detachment mechanism of the coatings were investigated. For this purpose, rectangular blocks were embedded in a carbon containing graphite cup. Then, the cup was placed in a tubular furnace containing nitrogen gas. After coating in different temperatures between 1200 and 1400 ˚C for 20 to 60 min soaking times, structure and microstructure of the coatings were investigated by X-ray diffraction, Raman analysis and scanning electron microscope equipped with energy dispersive spectroscopy (EDS). Moreover, the effect of coatings on the corrosion resistance of the alloy in an aqueous solution containing 5.2 mol HCl, 3.2 mol HNO3 and 3.2 mol HF was investigated. Results showed that the maximum thickness of the titanium carbo-nitride coating for the sample treated at 1400 ˚C for 60 min was about 50 μm. However, the possibility of coating detachment increased with increasing the coating temperature. It was due to the formation of Al-rich layer at the interface of the coating and the substrate and the formation of Ti3Al brittle phases, as well as the difference between the thermal expansion coefficient of the coating and the substrate. Corrosion test results showed that the formation of the coatings decreased the corrosion rate of the Ti-6Al-4V alloy from 130g.m-2.min-1 for the bare alloy to 10g.m-2.min-1.