Volume 42, Issue 3

The evolution of ideas concerning the nature of hydrogen embrittlement of engineering metallic materials is described based on a number of the proposed hypotheses and corresponding experiments. The main attention is paid to two of them, namely hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Recent attempts to interconnect the both models as HELP + HEDE and HELP-mediated HEDE ones are also estimated. A conclusion is made that HELP model is preferential for understanding the entire array of experimental data with a caveat that it is necessary to consider the chemical nature of hydrogen atoms and view them not only as point defects. Based on the studies of hydrogen effect on the atomic interactions in iron, nickel, titanium, and its alloys, it is shown that the electron approach to HELP phenomenon adequately describes two competitive features of hydrogen behavior in metals: increased brittleness and enhanced plasticity. Due to the increase in the concentration of free electrons, hydrogen decreases the elasticity moduli, which causes the crystal lattice to soften. For this reason, the formation of hydrogen atmospheres around the dislocations decreases the start stress of dislocation sources, as well as line tension of emitted dislocations, enhancing thereby their mobility, and weakens repulsion between dislocations in their pile-ups. The range of temperatures and strain rates in which hydrogen embrittlement occurs is controlled by the enthalpies of hydrogen atoms’ diffusion and their binding to dislocations. The resulting consequences for mechanical properties depend on the short-range atomic order, SRO, which inherently occurs in the metallic solid solutions and localizes plastic deformation both in the cases of short-range atomic ordering and of short-range atomic decomposition. Hydrogen enhances slip localization because of its different solubility in the submicrovolumes of short-range decomposed solid solutions. If SRO is absent or not remarkably formed, the hydrogen-increased concentration of free electrons results in enhanced plasticity. Available positive hydrogen effects on the plasticity of titanium β-alloys and austenitic steels are presented and interpreted.

Marine structures are constantly exposed to the corrosive effects of seawater, making effective corrosion protection crucial for their longevity and performance. Sacrificial anodes, commonly made of zinc, aluminum, or magnesium alloys, are widely employed to mitigate corrosion by sacrificing themselves to protect the steel structures. However, the selection and implementation of sacrificial anode materials present various challenges that need to be addressed. This paper explores the challenges associated with sacrificial anode materials for steel structures and provides potential solutions. To overcome these challenges, the paper proposes solutions such as using advanced alloy compositions, protective coatings, hybrid anode systems, and improved design considerations. Furthermore, the importance of monitoring techniques to assess the performance and remaining lifespan of sacrificial anodes is emphasized. Several case studies and experimental findings are discussed to illustrate the effectiveness and limitations of sacrificial anode materials based on zinc alloys, aluminum alloys, and magnesium alloys. The paper highlights the need for ongoing research and development efforts to address the evolving demands of corrosion protection in marine environments.

The partitioning coefficient of the R12Na corrosion inhibitor is determined by relating its concentration in the water phase ( C W ) to the expected theoretical concentration ( C i,T ) due to a re-concentration phenomenon after the mixing stage. Partition experiments were performed by varying the water cut in brine-kerosene mixtures, temperature, and the inhibitor concentration using NACE 1D182 brine as a water phase and ultraviolet-visible spectrophotometry. The partition results varied from 37.81 to 43.75 %, 36.68 to 61.23 %, and 40.29 to 56.47 % at 40 °C, 60 °C, and 80 °C, respectively, indicating that R12Na is a water soluble inhibitor and dispersible in the organic phase. Likewise, the partition results varied from 41.69 to 44.04 % in the presence of 20, 50, and 100 mg L −1 of the inhibitor, using a ratio of 80–20 vol% WP–OP and 60 °C. Furthermore, making the same considerations, the partition of different corrosion inhibitors reported in the literature was evaluated, supporting its determination, the latter is of great importance for dosing corrosion inhibitors in the oilfield industry.

In this study, in situ hybrid (Al 3 Ni + Al 2 O 3 )/Al composites were prepared successfully by the solid-state combustion via Al–NiO system. The effects of Al 3 Ni + Al 2 O 3 on the corrosion features of composites were analyzed using potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion corrosion in 3.5 wt% NaCl solution. The results show that with the increase of NiO addition, the corrosion resistance of composites is improved, and the corrosion resistance of 15 % NiO–Al composite is almost comparable to the Al matrix. The increased quantity and dispersive distribution of Al 3 Ni and Al 2 O 3 particles can effectively prevent the occurrence of corrosion and the movement of free electrons. Besides, more fine Al 2 O 3 particles distributed in grain boundaries can increase the impedance and hinder the electrochemical corrosion preferentially starting at the boundary. Also, in the composite with high NiO addition, a better and compact interface bonding can be formed due to reduction of large size Al 3 Ni particles and improvement in the dispersion of particles, thereby inhibiting interface damage. This study has advanced understanding of corrosion.

Repassivation characteristics of carbon steel experienced thermal cycles in tropical marine environments were investigated in a simulated concrete pore solution (SCPS). The results suggested that the damage of passive films on the carbon steel mainly occurred during the cooling process in thermal cycles. The damaged passive films gradually recovered in the SCPS, and the duration of repassivation extended with the amplitude of thermal cycles and cyclic number in the high-amplitude thermal cycles (20–60 °C and 20–70 °C), while it was not significantly affected by the cyclic number in the low-amplitude thermal cycles (20–40 °C and 20–50 °C).

The present study presented the systematic investigations on the influence of Co and Cu on the corrosion behaviors and wear resistance of Ti–Nb based shape memory alloys. The results demonstrated that the addition of Co and Cu can effectively enhance the corrosion resistance of Ti–Nb based shape memory alloys. By optimizing the chemical composition, the superior corrosion resistance with ( φ corr  = –0.95499 V, J corr  = 357.92 μA cm −2 ) and ( φ corr  = –0.96775 V, J corr  = 467.54 μA cm −2 ) can be obtained in Ti–Nb–Co 1.0 and Ti–Nb–Cu 1.5 shape memory alloys, respectively. Similarly, the wear properties of Ti–Nb based shape memory alloys were also dependent on the ternary alloying elements. The friction coefficient of Ti–Nb based shape memory alloy firstly decreased and then increased with the content of ternary alloying element increasing. And then decreased again, as the exceeding ternary alloying element was added. In addition, the wear behaviors of Ti–Nb based shape memory alloys can be attributed to the combination of abrasive wear, adhesive wear, and oxidative wear, irrespective of the types of ternary alloying elements. In contrast, Ti–Nb–Cu 5.0 shape memory alloy has the lowest friction coefficient of 0.45, which is smaller than that (0.50) of Ti–Nb–Co 5.0 shape memory alloy.

In this work, the distribution of hydrogen (H) atoms at a notch on an X52 pipeline steel under various applied loads or displacements were investigated by Volta potential measurements using a scanning Kelvin probe (SKP) and finite element modeling. The stress concentration at the notch is elastic under the test condition. The H atom diffusion and distribution is driven by stress, rather than strain, in the steel. However, when displacements are applied on the steel specimen, the strain dominates the H atom distribution. As the local stress or strain increases, the H atom concentration increases, as indicated by negative shifts of the Volta potential. By establishing the quantitative relationships among Volta potential, von Mises stress, and H atom distribution, this work attempts to provide a novel method for H atom detection in steels through the Volta potential measurement.