Iranian Journal of Materials Science and Engineering

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Abstract: Electroless Nickel (EN) composite coatings embedded with Cr2O3 and/or MoS2 particles were deposited to combine the characters of both Cr2O3 and MoS2 into one coating in this study. The effects of the co-deposited particles on corrosion behavior of the coating in 3.5% NaCl media were investigated. The results showed that both Ni-P and Ni-P composite coatings had significant improvement on corrosion resistance in comparison to the substrate. Codeposition of Cr2O3 in coating improved corrosion characteristic but co-deposition of MoS2 decreased corrosion resistance of the coating.

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Microstructure and corrosion performance of admiralty brass (ADB) and aluminum brass (ALB) alloys after passing different annealing heat treatments were investigated using optical and scanning electron microscope, energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), DC polarization measurements and electrochemical impedance spectroscopy (EIS). The results showed that heat treating of ALB caused gradient in aluminum concentration across the grains whose increased with increasing of annealing temperature. On the other hand, corrosion current density (i corr) of ADB in 3.5%NaCl media decreased with increasing of recrystallization, while ALB showed corrosion behavior inconsistent with ADB. The impedance measurements showed that corrosion rate of ADB decreased with increasing of exposure time from 0 to 15 days which could be related to the formation of SnO 2 surface film and the Sn-rich phases. While polarization resistance of ALB decreased by passing days in the corrosive media which could be associated to establishing of differential aluminum concentration cells.

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The effect of anodic oxidation of a NiTi shape memory alloy in sulfuric acid electrolyte on its surface characteristics was studied. Surface roughness was measured by roughness tester. Surface morphology was studied using optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion behavior was specified by recording Potentiodynamic polarization curves and measuring the content of Ni ions, released into a SBF solution using atomic absorption spectroscopy (AAS). Fourier transformation infrared radiation (FT-IR) and energy dispersive spectroscopy were employed to verify the biocompatibility of the anodized and bare alloys after submersion in SBF. It was shown that anodic oxidation in sulfuric acid significantly increases corrosion resistance and biocompatibility. This layer improves corrosion resistance and Ni ion-release resistance by impeding the direct contact of the alloy with the corrosion mediums i.e. Ringer and SBF solutions. The TiO2 oxide layer also decreases the releasing of Ni ions in to SBF solution

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The lean duplex stainless steels (LDSS) have excellent features due to the microstructural phase
combination of austenite and ferrite grains. These steels have low Ni and Mo contents which can reduce the cost
and stabilize the austenite fraction in the microstructure. In recent years, welding is used to enhance the
microstructural behaviour of LDSS. In this paper, Gas tungsten arc welding (GTAW) was performed on LDSS
S32101 with different heat energy inputs and varying welding currents. The influence of heat inputs (0.85 and 1.3
kJ/mm) on welded samples was investigated to study the microstructural behaviour, phase balance, and mechanical
& corrosion performance. The microstructures studies were carried out using an optical microscope, scanning
electron microscope and X-ray diffraction. The effect of Heat input led to the significant microstructural evolution
in weld metals with high austenite reformation. The microstructure of weldments consisted of inter-granular
austenite (IGA), grain boundary austenite (GBA) and Widmanstatten austenite (WA). Important mechanical
properties such as tensile strength and micro-hardness were investigated to understand the performance of
weldments. The polarization method was used to understand the corrosion behaviour of weldment in a 3.5% NaCl
solution. The experimental results showed enhanced properties of welds that could be suitable for industrial
applications.

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In this research study, a composite coating of Ni-Co/SiC-CeO₂ was prepared on a copper substrate using the pulse electrodeposition technique. The effects of electrodeposition parameters, including current density, duty cycle, and frequency, on the properties of the prepared coating were investigated. The selected current density values were 0.1, 0.2, and 0.3 A/cm², the duty cycle options were 10, 20, and 30%, and the frequency values were 10, 100, and 1000 Hz. Increasing the current density enhanced the microhardness of the coating but reduced its corrosion resistance. This behavior can be attributed to the grain refinement occurring within the coating as the current density increases. On the other hand, an increase in duty cycle resulted in a decrease in microhardness, which can be attributed to a decrease in the concentration of nanoparticles within the coating. The lower corrosion resistance observed at higher duty cycles could be attributed to the decrease in off-time, causing the pulse electrodeposition conditions to approach a DC (direct current) state. Furthermore, higher frequencies were found to be associated with increased microhardness and improved corrosion resistance of the coatings. The coatings with the highest corrosion resistance exhibited a corrosion current density of 0.29 µA/cm² and a polarization resistance of 1063 Ω.cm² in a 3.5% NaCl solution. These coatings were prepared using a current density of 0.2 A/cm², a duty cycle of 10%, and a frequency of 1000 Hz.