Iranian Journal of Materials Science and Engineering

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The effects of H2SO4 concentration on the electrochemical behaviour of passive films formed on AISI 304 stainless steel were investigated using by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization indicated that the corrosion potentials were found to shift towards negative direction with an increase in solution concentration. Also, the corrosion current densities increase with an increase in solution concentration. Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott– Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. EIS data showed that the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants is applicable.

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In this study, effect of immersion time on the electrochemical behaviour of AISI 321 stainless steel (AISI 321) in 0.1 M H 2SO 4 solution under open circuit potential (OCP) conditions was evaluated by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott–Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with the immersion time. EIS results showed that the best equivalent circuit presents two time constants: The high-medium frequencies time constant can be correlated with the charge transfer process and the low frequencies time constant has been associated with the redox processes taking place in the surface film. According to this equivalent circuit, the polarization resistance (interfacial impedance) initially increases with the immersion time (1 to 12 h), and then it is observed to decreases. This variation is fully accordance with potentiodynamic polarization results

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Four compositions of austenitic Mn-Cr steels have been developed successfully for in-vessel component materials in power plant industry. The phase stability of these Mn-Cr steels was studied by and X-ray diffraction (XRD) patterns. XRD patterns have shown that the matrix of these Mn-Cr steels is a single γ-phase structure. The potentiodynamic polarisation curves suggested that these fabricated Mn-Cr steels showed passive behaviour in 0.1M H2SO 4solution. Therefore, semiconducting behaviour of passive film formed on these fabricated Mn-Cr steels in 0.1M H2SO 4 solution was evaluated by Mott–Schottky analysis. This analysis revealed that passive films behave as n-type and p-type semiconductors. Based on the Mott–Schottky analysis, it was also shown that donor and acceptor densities are in the order of 1021 cm -3 and are comparable for other austenitic stainless steels in acidic environments

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In this study, corrosion behaviour of A356-10 vol.% SiC composites casted by gravity and squeeze casting is evaluated. For this purpose, prepared samples were immersed in HCl solution for 1h at open circuit potential. Tafel polarization and electrochemical impedance spectroscopy (EIS) were carried out to study the corrosion resistance of composites. The Tafel polarization and EIS studies of the corrosion behaviour of the A356-10 vol.% SiC composites showed that the corrosion resistance of the composite casted by squeeze casting was higher than that of the composites casted by gravity in selected corrosion media. Also, the Tafel polarization and EIS studies revealed that the corrosion current densities of both composites increase with the increase in the concentration of HCl. The micrographs of scanning electron microscope (SEM) clearly showed the squeeze casting composite exhibits a good dispersion/matrix interface compared to that of the composites produced by gravity casting

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The main purpose of this investigation is to assess the effect of post-deposition annealing treatment on the electrochemical behavior of TiN coating developed on AISI 304 stainless steel substrate using cathodic arc evaporation physical vapor deposition (CAE-PVD). Post-annealing treatment at 400 ºC was performed on the coated substrate for 1 h. The studied samples were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. The preferred orientation of TiN (111) was identified by XRD patterns and the crystallinity of the coating increased after annealing treatment. SEM observations indicated that TiN coatings free of cracks were successfully developed on the substrate. The electrochemical measurements elucidated that the annealed coating had better corrosion resistance compared to that of the as-deposited coating with a lower current corrosion density. This investigation implied that improved corrosion performance of the TiN coating can achieved by performing post-deposition annealing treatment.

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In this study, CrN/ZrN multilayer nanostructured coatings with different bilayers (10, 20, and 30) were created by the cathodic arc evaporation. The electrochemical behavior of samples was evaluated by polarization and impedance spectroscopy tests in the Ringer medium and the pin on disk test was used to investigate the tribological behavior of the samples. The results of measurements showed that the electrochemical and tribological behavior of the coatings depends on the number of bilayers and by rising the number of bilayers, the coating shows higher corrosion resistance and better tribological performance. Field emission scanning electron microscopy (FE-SEM) images of the specimens after exposure to the corrosion medium showed that the number of surface cavities were formed by the coating that had the highest number of bilayers comparing with other coatings were quite fewer in number and smaller in diameter. The results of the pin on disk test showed that by increasing the number of bilayers from 10 to 30, the coefficient of friction and wear rate decreased and the 30L coating ‌showed better wear resistance.

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In this study, for the first time, the Forsterite (Mg₂SiO₄) nanoparticles (NPs) with the size of about 25 nm were added to the phosphate-based electrolyte, and the characteristics and properties of the obtained plasma electrolytic oxidation (PEO) coating on AZ31 Mg alloy was investigated. The results of the potentiodynamic polarization measurements revealed that after one week of exposure to simulated body fluid (SBF) solution, the coating with Mg₂SiO₄ NPs possessed 12.30 kΩ cm² polarization resistance, which was more than two times greater than that of the coating without NPs. The thicker coating layer, lower wettability, and also presence of Mg₂SiO₄ NPs inside the pores were responsible for enhanced corrosion protection in the Mg₂SiO₄ NPs incorporated coating. After three weeks of immersion in SBF solution, the in-vitro bioactivity test results indicated the ability of the NPs-containing coating to form apatite (Ca/P ratio of 0.92) was weaker than the coating without NPs (Ca/P ratio of 1.17). This could be attributed to the lower wettability of the coating with NPs and supports that the addition of the nanoparticles is not beneficial to the bioactivity performance of the coating. 

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This paper aims to study the tribological and electrochemical properties of the CrN/AlCrN nano-layer deposited on H13 tool steel. Arc physical technique was employed to deposit multilayer coating. X-ray diffraction technique, thermionic and field emission scanning electron microscopy and energy dispersive spectroscopy have been used to determine the characteristics of the samples. To study the samples' wear behavior, coating adhesion, and surface hardness, reciprocating wear test, Rockwell-C test, and microhardness Vickers tester were employed, respectively. The measured values of the coefficient of friction and the calculated wear rates showed that the CrN/AlCrN multilayer coating has a much higher wear resistance than the uncoated sample. The coefficient of the friction of the coated sample was 0.53 and that of the uncoated sample was 0.78. Moreover, the wear rate of the coated H13 steel was about 127 times lower than the bare H13 steel sample. The results obtained from electrochemical impedance spectroscopy and polarization tests demonstrated that the corrosion current density of the H13 steel sample was 8 μA/cm2 and that of the CrN/AlCrN multilayer-coated sample was 3 μA/cm2. In addition, the polarization resistance of the treated and the substrate specimens was estimated at 4.2 and 2.7 kΩ.cm2, respectively.

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The principal goal of this research is to produce a CrN/Cu multilayer coating and a CrN single-layer
coating and also compare their electrochemical and antibacterial behavior. In this investigation, the coatings were
applied to the stainless steel substrate by cathodic arc evaporation a sub-division of physical vapor deposition
(CAE-PVD). The present phases were characterized and the thickness of the coatings was measured using X-ray
diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. Rockwell-C tester was
used to evaluate the adhesion quality. Also, to evaluate the mechanical properties of the coatings such as modulus
of elasticity and hardness, a nanoindentation test was used and the indentation effect and coating topography were
evaluated using atomic force microscopy (AFM). Studying the electrochemical behavior of the coatings was done
using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests in Ringer's
solution. The results of EIS tests showed that the CrN coating had higher polarization resistance in comparison to
the CrN/Cu coating and an increasing trend of polarization resistance related to both coatings was identified by
rising the time of immersion. Also, using the PDP curves, the CrN and CrN/Cu coating current densities were
estimated at 1.835×10-8 and 2.088×10-8, respectively. The antibacterial activity of CrN and CrN/Cu coatings was
evaluated by the spot-inoculation method. The results of the antibacterial test indicated that compared to CrN
coating, CrN/Cu coating had a better impact on the control of the bacteria growth.