جستجوی مقالات مرتبط با کلیدواژه « corrosion resistance » در نشریات گروه « مواد و متالورژی »

In this research, the properties of zinc phosphate (single cation), zinc/nickel (double cation) and zinc/nickel/manganese (three cation) coatings were investigated.

The basic phosphating solution was prepared based on previous experiences including phosphoric acid, nitric acid, accelerators and modifiers to create an optimal coating structure. The concentration of compounds and operational parameters of temperature, time and solution pH were fixed during the process. The amount of zinc-nickel-manganese cations by zinc oxide is 1.5; Nickel nitrate 4 and manganese carbonate 3.8 (g/liter) were added to the bath. In the zinc phosphate coating solution (monocation), manganese nitrate and nickel nitrate were removed from the solution in Table 1. Zinc/nickel phosphating solution (bi-cationic) was also obtained by removing manganese carbonate from the solution. Measuring the thickness and weight of the surface unit, determining the amount of total and free acid, studying the morphology and microstructure of the coating; Corrosion resistance tests including resistance to alkali solubility, salt spray test were performed. Also, after painting the phosphated samples, paint layer thickness test, scratch and bending test, impact test and paint layer hardness were performed.

The comparison of phosphating baths showed that the weight of the coating decreased with the introduction of nickel and manganese ions. The low zinc phosphate coating has a cluster structure, while the zinc-nickel phosphate coating crystals are clustered and sheet-like, and the tri-cationic phosphate coating has a mixture of cubic and sheet-shaped structures. The difference in height and height in zinc-nickel-manganese phosphate coating; It has the lowest Ra and Rz values compared to single-cationic and double-cationic phosphate coatings. Also, the optimal three-cation coating has the highest corrosion resistance, which is due to greater uniformity, less porosity, fine crystal structure, and a high percentage of corrosion-resistant phases in the coating composition.The coating color studies indicate that the best adhesion of the paint layer is related to the tri-cationic coating. According to the researches, the zinc-nickel-manganese three-cation coating provided better results than the zinc-nickel and zinc-nickel two-cation coatings.

Plasma electrolytic oxidation is a new and upgraded method of anodizing process to improve the corrosion resistance of aluminum alloys by creating a ceramic coating on their surface.

One of the parameters affecting of PEO process as well as the performance of the prepared coatings is the composition of the substrate. In this study, the effect of increasing the percentage silicon of substrate on the plasma electrolytic oxidation process with bipolar pulse current in a silicate-based electrolytic bath was investigated. Scanning electron microscopy was used to evaluate the morphology and structure of the coating and X-ray diffraction test was used for phase detection. Coating corrosion behavior was evaluated by electrochemical tests after 1 hour immersion in 3.5% NaCl solution with the adjustment of pH 4.

coatings had a pancake structure with craters with irregular micro-cracks and micro-porosity. Investigations showed that with an increase in the percentage of silicon in the substrate, the thickness and porosity of the coatings decreased, and the volcanic morphology prevailed over the pancake morphology in the growth of the coating. Analysis showed the coatings mainly contain a mixture of γ- Al2O3, η- Al2O3, δ-Al2O3, SiO2, a small amount of mullite and some amorphous phases. Tofel polarization test revealed, in addition to reducing the corrosion current density up to 9% of the substrate silicon, we have seen an increase in the polarization resistance with the increase in the silicon percentage of the substrate after coating. The electrochemical spectroscopy test revealed that with the increase in the silicon percentage of the substrate, the coating forms a physical barrier against charge transfer substrate and the resistance of the outer layer decreases, but the resistance of the inner layer increases.

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.

Due to the efficiency of 17-4PH steel in gas turbines and contact with external particles such as dust and foreign objects, physical deposits such as oil vapors will undergo cracks, wear, and chemical corrosion during operation and will be removed from the cycle of use. Part replacement is not cost-effective due to the high cost of raw materials. In this research, the corrosion resistance of 17-4PH steel cladding and stellite6 on 17-4PH steel substrate was investigated by the Tafel polarization test; In the cyclic polarization curve for 17-4PH steel, the direct scan current density is lower than the reverse scan, and positive hysteresis is seen in the cyclic polarization curve. Also the partially formed passive layer is unstable and fragile. In the 17-4PH cladding, the direct scan current density is lower than the reverse scan, and positive hysteresis is observed in the polarization curve. Also the formed passive layer is resistant to the formation of new holes. In the cover of stellite6, according to the shape of this cover, it has high pitting corrosion resistance in this solution; It forms a negative hysteresis curve and its inverse curve is located in a lower current density than the straight curve; Therefore, the corroded areas can repair themselves by forming a passive layer. By examining the results, it was found that the corrosion rate of stellite6 and stainless steel claddings has decreased by 91% and 50% compared to the substrate.

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.

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.

Plasma electrolytic oxidation is a novel and promising method for coating the light alloys especially magnesium alloys. Several parameters affect the coating quality and its properties, where in this study; the effects of frequency on properties of coatings produced by PEO on AZ31 Mg alloy were investigated. The coating process was performed in a silicate-based electrolyte containing KF and K2TiF6 using a soft-sparking waveforms with 30 % cathodic pulse width at 1, 2, and 3 kHz. The surface morphology of the coatings was a net-like (scaffold) containing a micro-pores network, micro-cracks, and granules of oxide compounds, in which, no noticeable change on coating morphology occurred with increasing the frequency. Also, the coatings were composed of MgO, MgF2, Mg2SiO4, SiO2 (amorphous), and TiO2 (crystalline and amorphous) phases contributed by the elements from both substrate and electrolyte in the coating process. Based on the cross-sectional images, the thickness of coatings displayed no significant increase with increasing in frequency, but the porosity percentage was increased. Also, the very small pores were presented in the inner layer with increasing frequency. Corrosion behavior of the coatings was evaluated using electrochemical impedance spectroscopy (EIS) in 3.5 wt. % NaCl until 7 days of immersion. The results of the EIS showed that with increasing frequency and porosity, the larger surface of the coating is in contact with the solution, and the presence of porosity in the more compact layer of the coating allowed the access of solution to the substrate, which reduces the barrier performance of the coating.

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.