The effectiveness of 6-(N-morpholino)-2-carboxypyrazine (MCP) as a corrosion inhibitor for mild steel in 1 M hydrochloric acid was systematically assessed using weight loss measurements, electrochemical techniques, and quantum chemical calculations. Various concentrations of the inhibitor (0.0-0.5 mM) and immersion times (1-48 hours) were tested at 303 K, along with temperature variations (303-333 K) to evaluate thermodynamic parameters. The inhibition efficiency increased with concentration, peaking at 81.9% from potentiodynamic polarization and 83.8% from weight loss at 0.5 mM, with moderate enhancement observed at higher temperatures, indicating a chemisorptive interaction. The adsorption behavior followed the Langmuir isotherm, suggesting the formation of a monolayer on the metal surface. Potentiodynamic polarization studies identified MCP as a mixed-type inhibitor, effectively slowing both anodic metal dissolution and cathodic hydrogen evolution. Density functional theory (DFT) computations corroborated these findings by indicating a low HOMO-LUMO energy gap and favorable charge distribution, which align with strong surface adsorption. Together, these experimental and theoretical results position MCP as a thermally stable, electronically active, and surface-affinitive corrosion inhibitor, presenting promising potential for the development of protective coatings for steel structures in acidic environments.
This study demonstrates the comparative properties of titanium chromium nitride (TiCrN) films deposited by direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and inductively coupled plasma magnetron sputtering (ICPMS). The crystal structure and microstructure of the deposited films exhibited significant dependence on the sputtering mode employed. The introduction of mfMS and ICPMS deposition processes resulted in a transformation of the film morphology from a porous columnar structure to a denser configuration characterized by finer grains. The surface roughness and crystal grain size of the coated films were assessed using non-contact atomic force microscopy (AFM) and Xray diffraction (XRD) analyses. A high-precision nanoindentation tester was utilized to measure the nano-hardness and elastic modulus of the TiCrN films deposited by three sputtering techniques: dcMS, mfMS, and ICPMS. Additionally, to conduct a comparative analysis of the effects of the sputtering modes on the corrosion resistance of the TiCrN films, a potentiodynamic polarization test was performed, allowing for evaluation of these effects through electrochemical analysis.
This study investigates the effect of minor Mo addition in Cr-bearing ultra-high-strength pipeline steel on microstructure, hydrogen transport behavior, and corrosion response. Two steels with different Mo contents were produced through quenching and tempering, and their characteristics were analyzed using electron backscatter diffraction (EBSD), electrochemical hydrogen permeation testing (HPT), and electrochemical impedance spectroscopy (EIS). EBSD analysis revealed that increased Mo content refined the tempered martensitic lath structure and reduced the prior-austenite grain size, indicating suppressed grain growth during heat treatment, which influences hydrogen transport and trapping behavior in the steel. HPT results demonstrated that hydrogen permeation during the charging stage was similar for both steels; however, a clear difference emerged during the desorption stage. The higher Mo content resulted in a faster decrease in permeation current during the decay transient, indicating greater hydrogen trapping efficiency. This behavior is associated with interactions between hydrogen and microstructural features, including Mo-containing precipitates and associated lattice distortions. EIS results further indicated that the higher-Mo steel exhibited increased polarization resistance during prolonged immersion, suggesting improved long-term corrosion resistance. These results suggest that increasing Mo content enhances hydrogen trapping efficiency and surface stability of the Cr-bearing ultrastrong steels, improving durability for hydrogen transport applications.
In this study, the time-dependent localised corrosion behaviour of UNS K32045 steel in 3.5 wt% NaCl solution was investigated using potentiodynamic polarisation, immersion testing, optical observation, SEM-EDS, and Raman spectroscopy. The microstructure mainly consisted of tempered lath martensitic structure with lath packets distributed across the observed surface, providing heterogeneous sites for corrosion initiation. Potentiodynamic polarisation revealed a continuous increase in anodic current without an active-passive transition, with a slope change near -0.40 V (SSE) . This response indicated that the anodic behaviour was associated with the initiation and propagation of localised corrosion in a chloride-containing environment rather than activation-controlled dissolution. Immersion tests showed that mass loss increased with exposure time, although the increase was not constant. The increase was relatively large during the early stage and became less pronounced after longer immersion in the solution. Optical observation revealed that corrosion products formed and became more widely distributed over time, progressively covering the exposed surface. SEMEDS analysis showed that corroded regions were partially covered with rough, porous corrosion products containing oxygen and chlorine. Raman spectroscopy confirmed that the surface products consisted of mixed iron oxyhydroxides. These results demonstrate that localised corrosion and corrosion-product accumulation developed concurrently with immersion time on the exposed surface.
Hot press forming (HPF) steels are widely used in automotive applications; however, their corrosion performance is significantly influenced by the coating microstructure. Although Al-Si and Zn-based coatings are commonly applied, the relationship between microstructural characteristics and electrochemical behavior is not yet well understood. This study investigates the corrosion behavior of Al-Si-coated and Zncoated HPF steels using an integrated approach that combines electron backscatter diffraction (EBSD) analysis with electrochemical techniques. Microstructural characteristics were directly correlated with electrochemical responses obtained from open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and galvanostatic testing. The Al-Si-coated HPF exhibited a dense and continuous Fe-Al intermetallic multilayer structure, which provides effective barrier-type protection and stable electrochemical behavior. In contrast, the Zn-coated HPF displayed a heterogeneous microstructure with Fe-Zn phases and surface oxides, leading to localized electrochemical activity. EIS results indicated a simple and stable response for the Al-Si coating, while the Zn coating exhibited complex behavior associated with adsorption-related processes. These findings were consistent with polarization and galvanostatic results, confirming higher corrosion activity in the Zn coating. Overall, this study demonstrates that the corrosion behavior is strongly governed by coating microstructure, highlighting its importance in understanding corrosion mechanisms.
