corrosion behavior

Nickel-titanium alloys have poor hardness and tribological properties. There is a possibility of loosening caused by wear while using these alloys for medical applications such as artificial bone joints. The hardness, wear resistance, and corrosion resistance of the surfaces can be improved by deposition of coatings such as TiN. The study's main objective was to investigate how the deposition atmosphere affects the morphological and microstructural properties and the mechanical and corrosion behavior of the coatings.

This study demonstrates the effective use of the dense plasma focus method to deposit titanium nitride coatings onto nickel-titanium shape memory alloys in various atmospheric conditions. The atmospheres used were (i) 50 vol. % argon and 50 vol. % nitrogen, and (ii) 75 vol. % argon and 25 vol. % nitrogen.

Nitriding process under the above-mentioned conditions increased the hardness of the samples. The average hardness of samples 0.5N2-7 and 0.25N2-7 were obtained to be ~ 459 HV and 410.5 HV, respectively. At a constant distance from the anode to the sample surface, with a decrease in the ratio of nitrogen to the total inlet gas, the sputtering rate in the chamber increases and leads to an increase in the coating thickness. The coating thickness of samples 0.5N2-7 and 0.25N2-7 were obtained to be 0.91 µm and 1.75 µm, respectively.

Scanning electron microscope images of the coating surfaces indicated that the nitriding process in the 75 vol. % argon and 25 vol. % nitrogen environment was more effective in preventing cracking. Additionally, lowering the nitrogen ratio in the atmosphere led to a higher sputtering rate within the chamber, contributing to an increase in coating thickness and improved corrosion resistance.

In this article, the effect of adding ZnO nanoparticles on the coating formed by electrolytic plasma oxidation (PEO) process in phosphate-based electrolyte on AM50 magnesium alloy was investigated. After choosing the electrolyte and optimal coating conditions, ZnO nanoparticles were added in different concentrations to the electrolyte solution and its effect on the structure and corrosion properties of the coatings was investigated. Corrosion resistance of the coatings was evaluated using polarization method and electrochemical impedance spectroscopy in 3.5% sodium chloride solution at ambient temperature and wear behavior of the coatings was checked by pin on disc method. The scanning electron microscope (SEM) was employed to determine the surface structure and the thickness of the coatings and their phase composition was surveyed by X-ray diffractometer. Phase analysis and microscopic images of the coatings showed that the addition of ZnO nanoparticles up to a certain amount reduces the porosity and increases the corrosion and wear resistance of the coating. The negative effect of adding too much ZnO nanoparticles is due to surface micro-cracks resulting from the stresses created on the surface of the coating. Finally, the coating formed in the electrolyte containing 15g/L trisodium phosphate, 5g/L sodium metasilicate and 1g/L ZnO nanoparticles, under the current density of 0.2 A/Cm2 for 5 minutes as the optimal coating in terms of corrosion and wear behavior and also the best morphology was selected.

Studies show that by applying coatings with amorphous structure on surgical instruments, the biocompatibility and corrosion resistance of these instruments can be increased. One of these coatings is Zr-based metal glass thin layer coatings. Therefore, in this research, after investigating the effect of different elements on the biocompatibility and corrosion behavior of coatings, first an alloy with the chemical composition of Zr30Cu20Al10Ag10Cr10Si10Br10 was designed and a thin disk of this alloy was produced using Spark Plasma Sintering, SPS, device. Then, thin layers of the alloy produced were applied on the 316 steel substrate using a Magnetron Sputtering machine. Initial investigations showed that the production coatings have a glass structure. Next, the hydrophobicity of the coating and its corrosion behavior in two environments, NaCl solution and Simulated Body Fluid was studied. The conducted tests showed that the application of the designed coating, by reducing the surfaces energy, increased the contact angle and as a result increased the hydrophobicity of the surfaces, transformed the surface of 316 steel from hydrophilic to hydrophobic. Also, the application of this coating due to its amorphous structure increases the corrosion resistance in the two environments of sodium chloride solution and Simulated Body Fluid. Examining the corroded surfaces indicates the occurrence of pitting corrosion phenomenon for the created coatings.

In this study,the surface structure,corrosion behavior of Monel 400 alloy are  comparatively investigated after high energymicro-shot peening process with its solution-annealed counterpart. To the aim of this investigation, microhardness, roughness measurements ,grazing-incidence X-ray diffraction  (GI-XRD),field-emission scanning electron  microscopy (FE-SEM), and transmission electron microscopy (TEM) were employed  to characterize the surface layers of high energy micro-shot peened andsolution-annealed samples. Based on the results,the process decreases the surface grain size from 30±4 µm to 76±5 nm,andincreases the density of dislocation structures on the surface. Moreover,electrochemical corrosion tests were carried out in HClsolution to compare the corrosion behavior of solution-annealed,micro-shot peened surfaces. Based on the results of thecyclic potentiodynamic polarization test,the micro-shot peened sample shows a higher initial corrosion current density at theexpense of a lower passivity current density,as compared with the solution-annealed one. The repassivation potential for themicro-shot peened sample is about +150 mV higher than the solution-annealed sample,which is a proof of the higher resistanceof this sample against localized corrosion. Based on the fitting of the data obtained from the electrochemical impedancespectroscopy,the polarization resistance of the passive film in the micro-shot peened sample is more than twice of this one forthe solution-annealed sample.

In the present study, the corrosion behavior of projection friction stir spot welding of 2024 aluminum alloy has been investigated and compared with the corrosion behavior of the base metal. Welding of sample was performed with the rotation speed of 2500 rpm and the dwell time of 12 seconds. The penetration depth of the tool on the surface of the sample was 0.1 mm, the diameter of the tool was 16 mm, and a circular protrusion with a diameter of 10 mm and a height of 0.4 mm was placed below the working table. By using Tafel polarization test method and standard Scanning Kelvin Probe through potential chang of weld surfaces and base metal as well as chang in corrosion current density, the corrosion behavior of projection friction stir spot welding was investigated. The results showed that the corrosion potential of the weld area is reduced compared to the base metal, although this reduction has not led to a significant increase in corrosion current density. Also, the welding zone has higher corrosion current density than the base metal region.

In this study, the effect of coating time on the microstructure and corrosion behavior of AZ31 Mg alloy coated by plasma electrolytic oxidation (PEO) method has been investigated. For this purpose, phosphate-based electrolyte containing hydroxyapatite nanoparticles was used at different times of 5, 10 and 15 minutes. The surface properties and chemical composition of the coatings were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) pattern. The corrosion properties of coatings in the simulated body fluid have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. The results of this study showed that with increasing the coating time to 15 minutes, the size of the pores and the thickness of the coatings increased. The coating created in 10 minutes has the lowest percentage of porosity among the samples. The results also showed that the coating created in 10 minutes had the lowest corrosion current density (2.33 × 10-8 A/cm2) among the samples.

Increasing the thickness of the oxide layer on the surface of the titanium alloy by electrochemical processes such as anodizing, leads to improved corrosion resistance and ultimately increase the lifespan of titanium implants in the human body. Among the parameters affecting the properties of the anodized layer, process voltage is of great importance with respect to kinetic and thermodynamic processes. In this paper, titanium substrate is subjected to anodizing process in sulfuric acid solution by different voltages such as 3, 6, 9 and 21 volts, electrolyte temperature of 60 ° C and duration of 30 seconds. Then the fuzzy, structural and morphological behavior, as well as the corrosion behavior of the coating are evaluated by GIXRD, FESEM and electrochemical tests such as electrochemical impedance in the simulated body fluid (SBF) solutionat 37 °C, respectively. GIXRD and FESEM analyzes show the formation of a titanium oxide coating with a hexagonal structure, which with increasing voltage up to 6 volts, a smoother and smoother surface was obtained, but further increase of voltage up to 9 and 21 volts, resulted in a rougher surface. Also, the results of corrosion behavior showed that increasing the anodizing voltage up to 6 volts due to the presence of a more uniform and smoother surface, which indicates less surface imperfections, led to the highest load transfer resistance in 1 and 24 hours of immersion in SBF solution at 37354 And 58127 (Ω .Cm2 ) compared to other anodized samples.

Corrosion is one of the most costly problems for the industry, which causes a lot of waste of time and manpower in this field. These costs can be directly related to the use of paints and inhibitors in the corrosion process, repair of metal parts or the use of steel, or indirectly affect the costs of damage, environmental hazards, closure or failure of a plant. . The aim of this study was to investigate the effect of temperature on the corrosion behavior of X70 micro-alloy steel in a sour environment in a solution of one molar of sulfuric acid in the presence of benzomidazole and methicbenzomidazole. With increasing temperature from 25 to 45 and 65° C, in the case of benzomidazole inhibitor, the protective layer formed on the surface is broken and less is formed at 25° C, as a result of this phenomenon, better adsorption is formed on the passive layer. The electron transfer is delayed, then the benzomidazole inhibitor is changed and subjected to an increase in temperature to 65° C, so that the protective layer increases again and the corrosion current does not decrease. From this decrease and increase of corrosion flow, a protective layer is formed at 45° C, which has relative adhesion and strength, and with increasing temperature up to 65° C, a protective layer begins to form at a lower potential. However, the protective layer is not recommended at all for this inhibitor. This is especially evident in X70 micro-alloy steel. Best Operating Temperatures Benzomidazole and methyl benzomidazole at room temperature are both inhibitors that improve corrosion resistance by increasing their amount in corrosion solution.

This study aimed to investigate the corrosion behavior of TiO2-N duplex coating formed by Plasma Electrolytic Oxidation (PEO) and gas nitriding. A TiO2 film formed on the titanium substrate by PEO in electrolyte containing sodium carbonate and sodium hydroxide in the first step. In the second coating process, the titanium substrate and the titanium oxide coated substrate was nitrided in a tube furnace at 1000 oC for 6 hours to compare the corrosion properties of the obtained coatings. X-ray diffraction, scanning electron microscopy of top-surface and cross-sectional structure of the layers, and potentiodynamic polarization along with electrochemical impedance spectroscopy was used to investigate the properties of the coatings. The XRD results showed that the titanium oxide coating consisted of a rutile phase, and the nitrified samples consisted of titanium nitride and TiO0.34N0.74 phases. The morphology of the coatings showed that the titanium oxide sample coating had micropores known as the pancake structure with a diameter of 4.1 microns on the surface. Also, the surface morphology of nitrided oxide-coated titanium indicates a slight change in the surface and a reduction in pore diameter of 2.8 microns due to the penetration of nitrogen in the titanium oxide coating. Finally, the results of impedance and polarization showed that the titanium oxide sample, due to its insulating and dense oxide structure, prevented the transfer of more corrosive ions to the metal surface, and its resistance was improved up to 10 times compared to other samples.

In this study, the nanocomposite coatings of Ni-W-P/SiO2 were produced by electrochemical co-deposition of SiO2 nanoparticles with Ni-W-P alloy in solutions with different amounts of these nanoparticles on the copper surface. The composition and structure of the coatings were studied with Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive Spectroscopy (EDS). The results showed that the incorporation of SiO2 particles in the Ni-W-P/SiO2 composite coatings increases the surface uniformity and smoothness of the coating. The open circuit potential (OCP), electrochemical Impedance (EIS) and potentiodynamic polarization (Tafel) techniques were used to evaluate the corrosion resistance of the coatings in 3.5% NaCl solution. The corrosion results showed that the Ni-W-P/SiO2 nanocomposite coatings were much higher corrosion resistance than pure Ni-W-P coating. By adding SiO2 nanoparticles to the solution, first the corrosion resistance increases and then decreases due to the agglomeration of the nanoparticles. The highest corrosion resistance was obtained for the synthesized composite coating from a solution containing 9 g/L SiO2 nanoparticles. The main reasons for the high corrosion resistance of this coating are the maximum amount of SiO2 reinforcing particles in metal matrix, nanometer structure without surface defects and micro-cracks.

The Copper/Graphene oxide composite sheets, containing 2% graphene oxide were made by accumulative roll bonding method in four steps for the first time. The process was performed at ambient temperature and non-lubricating conditions. The initial materials were commercial pure copper and graphene oxide. In order to evaluation the produced composites the mechanical, microstructural, electrical and corrosion behavior of the produced composites were investigated at different ARB cycles. The mechanical properties of the composite were investigated by tensile, micro hardness and fractography tests before and at different stages of the process. To observe structural changes a field emission scanning electron microscopy (FESEM) equipped with an EDX spectrometer were used. The results have shown that no new phase has been produced in this composite, and only the main peak of the copper, graphene and oxygen elements could be observed in the EDX patterns.The observation of microstructure showed that in lower cycles, graphene oxide powders were more agglomerated and had non-uniform distribution and in the final stages the powders distribution was more uniformly. The fractography results revealed ductile fracture of the produced composites. The corrosion resistance and electrical conductivity of composites increased compared to pure copper