corrosion resistance

The properties of coatings deposited by cold spray depend on the parameters of the process. The aim of this research is to investigate the effect of gas pressure and stand-off distance of cold spray process of zinc on a low carbon steel substrate.

In this research, zinc powder was sprayed at pressures of 20 and 30 bar and stand-off distances of 20 and 30 mm. The microstructure of the coatings was investigated using optical and scanning electron microscope and the micro-hardness of the coatings was measured. Then, the selected coating and steel substrate were subjected to polarization corrosion test.

The results showed that increasing the gas pressure from 20 to 30 bar decreased the porosity and increased the micro-hardness due to further deformation. Also, for a constant pressure, the stand-off distance of 20 mm has the lowest porosity and the highest micro-hardness due to the higher temperature of the particles when impact the substrate. The results obtained from the polarization test show that the coating has a sacrificial nature compared to the substrate and reduces the corrosion current density by 48% and corrosion rate by 33% compared to the substrate.

In this study, the effect of gas pressure and stand-off distance of cold spray process of zinc on low carbon steel substrate was investigated. The results showed that increasing the gas pressure from 20 to 30 bar and reducing the stand-off distance from 30 to 20 mm improved porosity and increased coatings micro-hardness. The results of this study can be used to optimize the parameters of the cold spraying of zinc for use in various industries such as automotive, power plants and marine infrastructure.

Recently, the consumption of non-ferrous alloys has increased significantly in the automotive industry due to their desirable properties, but according to the working conditions of car engine, it is necessary to apply coating to protect the surfaces and extend the lifetime of the car engine compartments. In this study, firstly, electrolytic plasma oxidation (PEO) is coated on the surface of the aluminium hydraulic tappet which is always in contact with the camshaft lobes, and then the metallurgical properties of the coating formed on the substrate in silicate and aluminate electrolytes are investigated. The results of the phase studies indicate that during the coating process, phases such as α-Al2O3 and γ-Al2O3 are created on the surface, moreover the plasma electrolytic oxidation coating resists against corrosion and wear strongly because of its favourable properties and quality. Compared to an uncoated sample, the corrosion rate and wear rate of coatings created in silicate and aluminate electrolytes decrease by 19 and 22 times, respectively, and by 6 and 9 times, respectively. Finally, the microscopic analysis reveals that the average diameter of the porosities in PEO coating formed in the silicate electrolyte is larger than that of coating generated aluminate electrolyte.

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.

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.

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.

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.