Stainless steel is one of the most commonly used structural materials in industry for the transportation of liquids such as water, acids, and organic compounds. Corrosion is a major concern in industry due to the use of strong mineral acids, feedstock contamination, flow, aqueous environments, and high temperatures. Stainless steel is the most commonly used material in the petrochemical industry because of its characteristics of self-protectiveness, offered by thin passive oxides, and its metallurgical composition. However, chlorides and mineral acids attack the stainless steel continuously, consequently breaking down the passivation film, causing a continuous challenge from corrosion. The corrosion in stainless steel is influenced by many factors including flow rate, temperature, pressure, ethanol concentration, and chloride ion content. This review describes the impact of organic compounds and organic acids on the degradation behavior of stainless steel. The review also summarizes the commonly used organic compounds and their applications. It has been demonstrated that organic acid concentration, temperature, and halide impurities have significant effects on susceptibility to pitting corrosion by damaging the passivation film. The phenomenon of corrosion in stainless steel is quite different in immersion tests and electrochemical potentiodynamic polarization. This review article discusses the importance of organic compounds and their corrosion behavior on steel. The article also puts emphasis on the roles of corrosion inhibitors, monitoring methods, corrosion management, and forms of corrosion.

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Aluminum alloys are widely used in a variety of industries nowadays for their high strength-to-weight ratio, good formability, low density, and recyclability. However, their poor corrosion and wear resistance properties restrict their applications. This study investigated the effects of electrical parameters and electrolyte compositions on the microstructures of micro-arc oxidation (MAO) film on a 7075 Al alloy substrate. The morphology, microstructure, and compositions of the MAO coatings were characterized using a scanning electron microscope (SEM), X-ray diffraction (XRD), and an electron probe micro-analyzer (EPMA). Furthermore, measurements of microhardness, corrosion resistance, and wear resistance were also conducted. The cathodic current and duty ratio are proportional to film thickness, which consequently improves the wear and corrosion resistance. The microstructural observations of the aluminate-based coatings revealed that increasing cathodic current reduces the pancake-like structures, and a lot of small pores appear on the top of the coatings, which makes the surface smoother. Moreover, the aluminate-based coatings are mainly composed of α-Al₂O₃ and γ-Al₂O₃, while the silicate-based coatings mainly consist of γ-Al₂O₃ and a small amount of α-Al₂O₃ phase. Due to the phase compositions, the microhardness of the aluminate-based coatings can reach 1300~1500 HV and exhibit better wear resistance than silicate-based coatings.

AZ61/carbon nanotubes (CNTs) (0, 0.1, 0.5, and 1 wt.%) composites were successfully fabricated by using the stir-casting method. Hall–Petch relationship and superposition of different strengthening mechanisms were analyzed for aged and as-cast AZ61/CNTs composites. Aged composites showed higher frictional stress (108.81 MPa) than that of as-cast (31.56 Mpa) composites when the grain size was fitted directly against the experimentally measured yield strength. In contrast, considering the superposition of all contributing strengthening mechanisms, the Hall–Petch constants contributed by only grain-size strengthening were found (σ₀ = 100.06 Mpa and K_f = 0.3048 Mpa m^1/2) for as-cast and (σ₀ = 87.154 Mpa and K_f = 0.3407 Mpa m^1/2) for aged composites when superposition law exponent is unity. The dislocation density for the as-cast composites was maximum (8.3239 × 1013 m⁻²) in the case of the AZ61/0.5 wt.%CNT composite, and for aged composites, it increased with the increase in CNTs concentration and reached the maximum value (1.0518 × 1014 m⁻²) in the case of the AZ61/1 wt.%CNT composite.

This paper deals with the tribological study of the laser remelted surfaces of the ECAP-processed AZ61 magnesium alloy and AZ61–Al₂O₃ metal matrix composite with 10 wt.% addition of Al₂O₃ nanoparticles. The study included the experimental optimization of the laser surface remelting conditions for the investigated materials by employing a 400 W continual wave fiber laser source. Tribological tests were performed in a conventional “ball-on-disc” configuration with a ceramic ZrO₂ ball under a 5 N normal load and a sliding speed of 100 mm/s. The results showed that both the incorporation of Al₂O₃ nanoparticles and the applied laser treatments led to recognizable improvements in the tribological properties of the studied AZ61–Al₂O₃ composites in comparison with the reference AZ61 alloy. Thus, the best improvement has been obtained for the laser modified AZ61–10 wt.% Al₂O₃ nanocomposite showing about a 48% decrease in the specific wear rate compared to the laser untreated AZ61 base material.