Corrosion and Materials Degradation

The effects of stacking configuration on the environmental durability of carbon fiber-reinforced polymer (CFRP) laminates were investigated under hygrothermal and salt spray aging. Unidirectional [0]_n and cross-ply [0/90]_n laminates were aged for up to 42 d, and their moisture absorption, chemical structure, dynamic mechanical behavior, flexural properties, and fracture characteristics were evaluated. Hygrothermal exposure produced higher moisture uptake and diffusion rates than salt spray, while the Langmuir model described the absorption behavior more accurately than the Fick model. After 42 d, the glass transition temperatures of the [0]_n and [0/90]_n laminates decreased by 23.8% and 23.7% under hygrothermal aging compared with 9.0% and 6.9% under salt spray. The corresponding flexural-strength losses were 16.1% and 18.6% versus 9.6% and 10.7%. Although the [0/90]_n laminate exhibited slightly lower moisture uptake, it suffered greater strength degradation because transverse cracking in the 90° plies promoted interfacial debonding and delamination. These results show that the environment governs degradation intensity, whereas stacking configuration controls damage propagation and flexural failure.

2-mercaptobenzimidazole (2-MBI) and propargyl-functionalized MBI (propargyl-MBI) as corrosion inhibitors for API 5L X70 steel in CO₂-saturated NaCl solution was evaluated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), gravimetric weight loss, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), and atomic force microscopy (AFM). Electrochemical tests showed that both inhibitors reduced corrosion, with propargyl-MBI exhibiting the best inhibition. propargyl-MBI achieving efficiencies of 96.1% by EIS and 97.4% by polarization at 10 ppm. After 96 h, corrosion rates decreased from 2.23 mm·year⁻¹ (blank) to 0.40 and 0.14 mm·year⁻¹ for 2-MBI and propargyl-MBI, respectively. SEM/EDS and AFM confirmed improved surface protection, with roughness decreasing from 142 nm (blank) to 76.8 nm (2-MBI) and 51.1 nm (propargyl-MBI). Adsorption followed the Langmuir model (R² = 0.99), with ΔG°ads values of −25.1 and −34.25 kJ·mol⁻¹ for 2-MBI and propargyl-MBI, respectively, indicating stronger adsorption after functionalization. Dispersion-corrected density functional theory calculations were used to elucidate the adsorption modes as well as the main interactions between the 2-MBI, in thiol and thione tautomers, and propargyl-MBI. The binding energy as well as the charge transfer were increased in the case of propargyl-MBI.

This study investigated the effects of Nb additions on the microstructure, hardness, and high-temperature oxidation behaviour of mechanically alloyed and spark-plasma-sintered Ti–48Al–2Cr–xNb alloys containing 1–5 at.% Nb. The aim was to clarify the role of Nb in phase evolution, strengthening, and oxidation protection, and to identify factors that limit its effectiveness. Following mechanical alloying and consolidation at 950 °C, the alloys exhibited predominantly globular γ-TiAl/α₂-Ti₃Al microstructures with localized Nb enrichment. Relative densities remained below 92%, indicating that residual porosity was a significant processing-related factor. The alloy containing 5 at.% Nb exhibited the highest hardness, consistent with Nb-induced solid-solution strengthening and changes in phase constitution. Isothermal oxidation was assessed by measuring weight gain per unit area after exposure at 700 °C for 400 h and at 900 °C for 200 h. At 900 °C, the alloys formed stratified scales consisting primarily of an outer TiO₂-rich layer and an underlying Al₂O₃-rich region. NbO₂ was detected in selected samples; however, no continuous, protective Nb₂O₅-rich scale formed. Preferential TiO₂ growth, together with cracking, exfoliation, and spallation, hindered the formation of a fully protective alumina barrier. At 700 °C, exposure for 400 h produced a substantially thinner, non-adherent oxide scale, consistent with the slower oxidation kinetics at lower temperatures. Consequently, increasing the Nb content did not result in a monotonic improvement in oxidation resistance. Overall, Nb enhanced hardness and influenced phase stability but did not, by itself, overcome the oxidation limitations of TiAl. Its effectiveness depends on densification, Al activity, microstructural homogeneity, and scale adhesion.