Atmospheric Seawater Research Articles

Exfoliated carbon nitrides for corrosion prevention in radiators: Temperature-dependent corrosion analysis

This article outlines the preparation and exfoliation of graphitic-carbon nitride (GCN) by thermal polymerization technique using urea proceeded by the hydrothermal approach for the application of corrosion resistance in radiators. The prepared sample was characterized by using various methods. X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the purity of GCN, and Surface morphology results revealed the formation of spherical-shaped GCN. Herein, graphitic carbon nitride (GCN) was synthesized to enhance its corrosion-resistance performance on mild steel (MS) under a seawater atmosphere. The corrosion behaviour of the graphitic-carbon nitride (GCN) synthesized by the hydrothermal method was examined by conducting electrochemical corrosion tests in a 3.5% NaCl medium under three different temperatures. The excellent temperature dependant electro-catalytic activity of the prepared GCN was analysed. The hydrothermal exfoliation process highly enhances the structural, optical, and electrochemical properties like corrosion resistance and stability of the prepared GCN. This study demonstrates that hydrothermally exfoliated GCN exhibits low corrosion rates and high electrochemical corrosion resistance, which could be a potential candidate for corrosion inhibitors in radiators.

Selective Corrosion of Socket Welds of Stainless Steel Pipes Under Seawater Atmosphere

Stainless steel has excellent corrosion resistance. The drawback is that pitting occurs easily due to the concentration of chloride. In addition, corrosion of socket weld, which is structurally and chemically weaker than the other components of the pipe, occurs rapidly. Since these two phenomena overlap, pinhole leakage occurs frequently in the seawater pipe socket welds made of stainless steel at the power plants. To analyze this specific corrosion, a metallurgical analysis of the stainless steel socket welds, where the actual corrosion occurred during the power plant operation, was performed. The micro-structure and chemical composition of each socket weld were analyzed. In addition, selective corrosion of the specific micro-structure in a mixed dendrite structure comprising γ-austenite (gamma-phase iron) and δ-ferrite (iron at high temperature) was investigated based on the characteristic micro-morphology and chemical composition of the corroded area. Finally, the different corrosion stages and characteristics of socket weld corrosion are summarized.

High Cycle Fatigue and Cyclic Plastic Deformation Behaviour of High Temperature Oxidation Resistant Titanium Aluminide Coated IMI 834 Alloy at 873 K

High cycle and force-controlled (HCF) as well as low cycle fatigue (LCF) behaviour of titanium alloy IMI 834 was comparatively studied in bare condition and with titani-umaluminide (Al2Ti) coating, at 873K in air, for compressor disc of aero engines. HCF testing of bare and Al2Ti coated IMI 834 alloy at 873 K in air revealed t hat the coated materials has higher lifetime than the bare alloy.However, for low cycle, high stress lifetimes, the unprotected bare alloy is stronger, possibly due to early crack formation and growth in coated layer. In the case of LCF tests at higher values of total strain amplitudes Al2Ti coated IMI 834 alloy has longer fatigue life (Nf ) as compared to the bare IMI 834 alloy which appears to be due to load shift-ing to the coat, but at lower values of total strain amplitude, Al2Ti coating on IMI 834 alloy seems to have no effect on Nf . Higher values of cyclic strength coeffici-ent (K0) and cyclic hardening exponent (n0) for coated IMI 834 alloy indicate that coating offers resistance to cyclic plastic deformation at 873 K in air, and hence is beneficial. The coating adheres well to the substrate and is also fairly resistant to high temperature corrosion in sea water atmosphere at 873 K.

The influence of high-temperature oxidation resistant titanium aluminide coating on low-cycle fatigue behaviour of titanium alloy IMI 834 at 600 °C

The low-cycle fatigue behaviour of titanium alloy IMI 834 was comparatively studied in bare condition and with titanium aluminide (Al2Ti) coating at 600 °C in air. Results revealed that at higher values of total strain amplitudes (Δ εt/2), Al2Ti-coated IMI 834 alloy has longer fatigue life ( Nf) compared to the bare IMI 834 alloy, which appears to be due to load shifting to the coat. At lower values of Δ εt/2, Al2Ti coating on IMI 834 alloy seems to have no effect on Nf. Higher values of cyclic strength coefficient ( K′) and cyclic hardening exponent ( n′) for coated IMI 834 alloy indicate that coating offers resistance to cyclic plastic deformation at 600 °C in air, and hence it is beneficial. The coating adheres well to the substrate and is also fairly resistant to high-temperature corrosion in sea water atmosphere at 600 °C.

Effects of Microstructure and Environment on Fatigue Properties of Investment Cast Ti-6Al-4V Alloy Welds

Effects of microstructural and environmental factors on fatigue crack propagation behavior of welded regions of cast Ti-6Al-4V alloy were investigated. Fatigue crack propagation tests were conducted for the welded regions, which were processed by two different welding methods: gas tungsten arc (GTA) welding and electron beam (EB) welding, under various load ratios (R=0.1, 0.9) and atmosphere (air, seawater). EB weld consisting of very thin α platelets had the faster crack propagation rate than the base metal and GTA weld, regardless of load ratio and atmosphere. Fatigue crack propagation rates at high load ratio (R=0.9) were faster than those obtained at low load ratio (R=0.1) and there was no crack closure at high load ratio (R=0.9), indicating that fatigue crack propagation at high load ratio was mainly controlled by intrinsic factors such as microstructure. Fatigue crack growth resistances in seawater atmosphere were slightly lower than those in air, but showed the similar trend with variation of specimen conditions. The degrees of crack closure were almost same regardless of specimen conditions in seawater atmosphere, suggesting that the fatigue crack propagation in seawater was mainly controlled by intrinsic factors such as microstructure.

The Effects of Residual Magnetism on the Corrosion Fatigue Properties of Type 410 Stainless Steel Compressor Blades

Abstract Residual magnetism is beneficial in improving the corrosion fatigue strength of Type AISI-410 stainless steel compressor blades tested in a synthetic sea water atmosphere. The corrosion fatigue strength of magnetized blades is improved 56% and survival time is increased 357% as compared with non-magnetized blades. The improvement is attributed to a reduction in the rate at which dislocations cross slip to broaden slip planes which are preferentially attacked by the corrosion media. X-ray diffraction studies confirm an interaction of dislocations and magnetic domain walls.