Cathodic protection is an effective strategy for mitigating corrosion in marine engineering applications. This study systematically investigates the evolution of surface states and corrosion resistance of 70/30 cupronickel tubes with pre-formed stable protective films under cathodic polarisation in natural seawater. Electrochemical impedance spectroscopy (EIS) and linear polarisation resistance (LPR) were employed to evaluate the electrochemical behaviour. Key findings reveal that a negative shift in polarisation potential (from -350 to -750 mV) reduces the barrier properties of the pre-existing protective film by nearly one order of magnitude, yet simultaneously accelerates the formation of a dense calcareous deposit layer. Notably, the innovation lies in the quantitative correlation between EIS-derived parameters and deposit growth: charge transfer resistance ( R ct) increases significantly from 14,260 to 44,790 Omega & centerdot;cm2, while the power index value of constant phase element (CPE) suggests the involvement of O2 diffusion in the electrochemical processes. The novelty is further highlighted by the identification of aragonite as the dominant phase in the calcareous deposits formed at -550 and -750 mV, which contributes to enhanced surface coverage.

This study investigates the effect of Na2S on the corrosion behavior of LPBF TC4 in artificial seawater using electrochemical tests and surface morphology characterization. The results showed that S2− reduces the corrosion resistance of LPBF TC4 alloy, and the degree of degradation intensifies with increasing concentration. X-ray photoelectron spectroscopy (XPS) analysis indicates that the content of TiO2 in the passive film decreases from 76.3 % to 58.7 %, and the content of Ti2O3 increases accordingly. The carrier density increases from 7.93 × 1019 to 1.17 × 1020 cm–3, and the point defect diffusion coefficient increases from 1.74 × 107 to 5.13 × 108 cm2 s–1. Based on these findings, a competitive adsorption–defect proliferation synergistic mechanism is proposed to explain the S2--induced degradation of the passive film. S2− competes with O2− for active adsorption sites and preferentially occupies oxygen vacancies in the passive film. This process suppresses the formation of compact and stable TiO2, promotes the generation of metastable titanium sulfide/oxysulfide species, and increases the concentration and diffusion rate of point defects. Consequently, the compactness and stability of the passive film are weakened, leading to enhanced ion transport and the initiation of localized corrosion.

Selective laser melting (SLM), a pivotal additive manufacturing (AM) technology for titanium alloys, enables near-net-shape forming of complex structures with relative densities of up to 99.9%, making it indispensable in aerospace, biomedical, and marine engineering. This review comprehensively updates the state of the art on SLM-fabricated TC4 (Ti-6Al-4V) alloy, addressing critical gaps in previous studies by integrating novel research progress, in-depth mechanistic analyses, and multi-dimensional comparisons. The core focus is on the unique thermal cycle (106–108 °C/s heating/cooling rates) of SLM, which induces a predominant needle-like martensitic α′ phase (99.7%) and minimal β phase (0.3%), leading to intrinsic anisotropy and low ductility. Room-temperature tensile strength reaches 1315.32 MPa with 9.6% elongation, and high-cycle fatigue limits the range from 417 to 829 MPa, strongly dependent on process parameters and post-treatment. Corrosion anisotropy is systematically analyzed: the XY plane (parallel to scanning direction) exhibits superior corrosion resistance in 1 M HCl (fewer pits and lower corrosion current density) and 3.5% NaCl (more stable passive film) compared to the XZ plane (deposition direction). Novel insights include: (1) synergistic effects of SLM process parameters (laser power–scanning speed–hatch spacing) on defect evolution and microstructure uniformity; (2) atomistic mechanisms of α′→α + β phase transformation during post-heat treatment; and (3) corrosion–mechanical coupling behavior in harsh environments (e.g., marine and biomedical). Post-treatment strategies are refined: annealing at 800 °C for 2 h achieves 1099 MPa tensile strength and 17.4% elongation, while hot isostatic pressing (HIP) reduces porosity from 0.08% to 0.01% and weakens fatigue anisotropy. This review also identifies unresolved challenges (e.g., in situ defect monitoring and multi-field regulated performance) and proposes future directions (e.g., AI-driven process optimization and functional gradient structures).

Titanium alloys are key structural materials for deep-sea engineering; however, the mechanism underlying their stress corrosion cracking behavior under deep-sea environment remains unclear. The stress corrosion cracking (SCC) characteristics of TC4 ELI alloy with equiaxed (EM) and Widmansta & uml;tten (WM) microstructures were investigated in a simulated 1000 m deep-sea environment (10 MPa, 4 degrees C, 3.5% NaCl). Results show that EM, with high alpha-phase content (>50%) and pronounced microtexture, exhibits higher SCC susceptibility (K-1SCC=66.79 MPa & sdot;m(0 & sdot;5)) and more distinct quasi-cleavage fractures than WM (K-1SCC=80.29 MPa & sdot;m(0 & sdot;5)). A "microstructure-electrochemistry-hydrogen" synergistic mechanism is proposed: For EM, the continuous alpha/beta network intensifies micro-galvanic corrosion, and microtexture bands accelerate pressure-driven hydrogen diffusion and enrichment at crack tips, thereby activating the Hydrogen-Enhanced Decohesion (HEDE) and Hydrogen-Enhanced Localized Plasticity (HELP) mechanisms. For WM, isolated alpha colonies, higher beta-phase fraction, and stable passive film attenuate galvanic corrosion and hydrogen transport. This study provides a theoretical basis for the microstructure optimization of TC4 ELI alloy in deep-sea engineering components.

The corrosion of copper as the disposal canister material was related to the form of bentonite in the deep geological repository (DGR). The corrosion behavior was investigated by the electrochemical tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) in a 0.1 mol/L NaHCO3 + 0.05 mol/L NaCl + 0.05 mol/L Na2SO4 solution. The results reveal that although bentonite can restrict oxygen diffusion, it accelerates copper corrosion in the short term due to the dissolved anions. In the top supernatant, corrosion-induced aggregation and detachment of bentonite lead to the decrease of its barrier property. However, the resulting increase in the corrosion rate promotes the formation of corrosion products, which ultimately protect the substrate from further corrosion. In the bottom slurry, local aggregation of the thicker bentonite layer does not fully compromise its barrier function. The corrosion products remain influenced by oxygen transport and exhibit a composition different from that formed in the supernatant. After copper immersion in the bentonite environment, a mixed layer composed of corrosion products and bentonite particles was observed on the surface. XPS results confirmed the presence of CuO, Cu2O, SiO2, silicates, Alsilicate, and Al2O3 in this mixed layer.

The strong oxidation of NaClO significantly influences the corrosion process of metal alloys in aqueous environment. This study investigates the corrosion behavior of B10 alloy in natural seawater with and without available chlorine using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and immersion tests. The results demonstrate that the corrosion rate of B10 alloy is accelerated with the increase of available chlorine concentration in seawater. The presence of available chlorine enhances the potential difference and promotes uneven potential distribution across the alloy surface. Immersion tests in seawater containing high concentrations of available chlorine reveal that the resulting corrosion products exhibit nickel depletion and chlorine enrichment.

In this paper, three different average surface roughness (Ra ) (0.023 μm, 0.143 μm and 0.334 μm) were used to study the effect of surface roughness on the pitting behavior of 304 stainless steel. It was characterized by electrochemical and surface analytical methods. The specimen with Ra of 0.023 μm showed higher corrosion resistance. With the increase of Ra, the pitting potential (Ep) decreased linearly, while the donor density (ND) of passive film on the surface of 304 stainless steel increased linearly. The smooth surface of 304 SS reduced the risk of pitting corrosion by increasing the Cr/Fe atomic ratio in the passive film. Accordingly, the pitting corrosion resistance was enhanced as surface roughness decreased.

Available chlorine is most commonly used in seawater cooling systems to eliminate biofouling. The corrosion behavior of 70/30 cupronickel alloy after exposure to seawater with different concentrations of available chlorine was studied by electrochemical and immersion tests. The electrochemical measurements show that 100 ppm available chlorine accelerates the corrosion of 70/30 cupronickel alloy in seawater. The corrosion rate of 70/30 cupronickel sample in seawater with 100 ppm available chlorine is 3-4 times higher than that in seawater with 0-10 ppm available chlorine. Scanning Kelvin probe (SKP) and scanning vibrating electrode technique (SVET) results demonstrate that the local electrochemical reaction of 70/30 cupronickel alloy is more active after soaking in seawater with 100 ppm available chlorine. Energy dispersive spectroscopy (EDS) results reveal that Cl element in the corrosion products is enriched after exposure to seawater with 100 ppm available chlorine. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the corrosion product of 70/30 cupronickel sample contains more Cu2(OH)3 Cl after being immersed in seawater with100 ppm available chlorine.

The stress corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo (Ti6321, in wt%) alloy in seawater with different dissolved oxygen (DO) concentrations was investigated using X-ray photoelectron spectroscopy, energy dispersive spectrometer, electrochemical measurements, and other advanced methodologies. The results indicate that when the DO concentration in seawater is insufficient, the passivation film will preferentially form on the alpha-phase surface. Meanwhile, insufficient DO concentration leads to incomplete oxidation of the surface passivation film, resulting in an increase in surface defects. Hydrogen produced by reactions at crack tips is more likely to enter the surface of the titanium alloy through these defects, and under the influence of HEDE and HELP mechanisms, promote crack propagation. The stress corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy in seawater with different dissolved oxygen (DO) concentrations was investigated using different methodologies. Insufficient DO concentration leads to incomplete oxidation of the surface passivation film. Hydrogen produced by reactions at crack tips is more likely to enter the surface of the titanium alloy through these defects, and under the influence of HEDE and HELP mechanisms, promote crack propagation. image

In this paper, the passive behavior of 304 stainless steel (SS) in NaCl solution is studied by electrochemical methods and surface analysis. The polarization measurement results show that the pitting potential (Ep) has a simple linear relationship with the temperature increase. Scanning Kelvin probe results show that the surface potential difference on the surface of 304 SS is well correlated with the temperature. Scanning electron microscope results show that the rupture of the passive film accelerates with the increase of temperature. The X-ray photoelectron spectroscopy analysis shows that the high temperature causes more oxidation on the surface of 304 SS, leading more Cr3+ oxidized to Cr6+ at high temperature.

The stress corrosion cracking (SCC) behaviors of Ti-6Al-3Nb-2Zr-1Mo (Ti6321, in wt.%) alloy samples with equiaxed microstructure (EM), bimodal microstructure (BM) and Widmanstätten microstructure (WM) in simulated 3000m deep sea environment were investigated using electrochemical tests, electron backscattered diffraction (EBSD), and so on. WM exhibits the best SCC resistance, which is attributed to its best self-healing ability, and is beneficial for the re-passivation of fresh metal at the crack tip. Besides, there is no obvious micro-texture region in WM with higher β phase, and α phase colonies hinder the dislocation movement, resulting in the lowest crack growth rate.

The double-layer NiCr-Cr 3 C 2 /Ni-Zn-Al 2 O 3 coatings with sufficient corrosion and wear resistance were prepared on low carbon steel substrates. The intermediate layers Ni-Zn-Al 2 O 3 were fabricated by using low-pressure cold spray (LPCS) method to improve the salt fog corrosion resistance properties of the supersonic plasma spray (SPS) NiCr-Cr 3 C 2 coatings. The friction and wear performance for the double-layer and single-layer NiCr-Cr 3 C 2 coatings were carried out by line-contact reciprocating sliding, respectively. Combined with the coating surface analysis techniques, the effect of the salt fog corrosion on the tribological properties of the double-layer coatings was studied. The results showed that the double-layer coatings exhibited better wear resistance than that of the single-layer coatings, due to the better corrosion resistance of the intermediate layer; the wear mass losses of the double-layer coatings was reduced by 70% than that of the single layer coatings and the wear mechanism of coatings after salt fog corrosion conditions is mainly corrosion wear.

Since thermally sprayed zinc and aluminum coatings were invented 100 years ago, they have realized extensive industrial applications for steel structure protection in a variety of fields for nearly 100 years and have been proven to be effective and reliable. However, it has seldom been reported in the ship industry in China since many workers worry about the risk of rapid corrosion, especially in harsh environments such as the South China Sea. In this paper, three kinds of arc-sprayed zinc aluminum coatings were tested to choose the best coating system for application on the research vessel Yongle by electrochemical behavior and a long-term atmospheric exposure experiment. The variation of the corrosion rate and the bonding strength was used to clarify the long-term protection performance. The results show that Zn15Al has the lowest corrosion (Rp larger than 2200 Ω·cm2) among the three kinds of coatings and has a bonding strength larger than 6.38 MPa after a 5 year test. The performance of the coatings in the South China Sea indicates that they can provide excellent protection for the hull above the waterline of the Yongle vessel in the 3 year test. It could be predicted that thermally sprayed zinc aluminum coating has vast application potential in the South China Sea due to its excellent anticorrosion performance.

海水管道焊缝下游区是发生腐蚀的热点区域.为探究B30管道焊缝余高对与其下游区腐蚀行为的影响,利用原位电化学测试装置和自制循环海水冲刷装置,在3天、7天、15天、30天4个冲刷节点进行试验.测试了3种模拟焊缝余高(0 mm;0.5 mm;1.5 mm)在紧邻热影响区和下游30 mm处母材区的电化学阻抗谱,用扫描电镜观察了试样表面的腐蚀形貌,结合COMSOL软件建立了有限元仿真流态模型,探讨了余高对介质流态的影响.结果表明,在有焊缝情况下,热影响区和母材区阻抗值均小于无焊缝结构,焊缝结构会加速下游区的腐蚀,且余高越大,腐蚀倾向也越大;热影响区腐蚀速率均大于母材区;流态模型显示出在热影响区位置出现了涡流,涡流加速了热影响区的腐蚀.

Available chlorine is known to play a significant role in metal corrosion due to its oxidising properties. In this paper, the effect of available chlorine concentration on corrosion behaviour of the low alloy marine steel was investigated by electrochemical and immersion tests. Experimental results show that the corrosion rate of low alloy marine steel is accelerated with the increase of available chlorine concentration in seawater. The localised electrochemical dissolution of the steel is more active with the concentration of available chlorine increasing. Energy dispersive spectroscopy (EDS) was performed to understand the composition of the corrosion products that the large enrichment of Cl element occurred for the high available chlorine concentration (100 ppm) after 720 h exposure to seawater. The influence of available chlorine concentration on mechanical property of low alloy marine steel indicatesthe less impact on the tensile and yield strength of the low alloy marine steel.

Failure analysis of a heat exchanger made of 70/30 cupronickel was investigated in this paper. The heat exchanger tubes showed leakage failure after one year of service. The maximum thinning regions were mainly distributed in the lower region near the tube inlet along the flow direction. Visual examination, chemical composition analysis and microstructure characterization were conducted to determine the root cause of the failure. Visual investigation revealed the perforation was initiated from the inner wall of the tube. Microscopic examination showed that the heat exchanger tube failed as a result of severe pitting corrosion. The chloride presence and denicklification were found in the corrosion pits. The aggressive environment generated under deposits caused the phenomenon of localized corrosion.

通过可原位测量的管流式实验装置,采用电化学阻抗谱等电化学方法研究B10管在不同温度的天然海水中的腐蚀行为,采用SEM、XPS等方法分析其腐蚀形貌及腐蚀产物成分.结果表明,在10～50℃范围内,随着温度的降低,B10管表面的腐蚀产物膜逐渐致密,膜层耐蚀性逐渐升高,腐蚀速率逐渐降低.在10、25和35℃时,B10管的腐蚀速率随时间的延长逐渐降低,腐蚀产物主要为Cu2O、NiO和FeOOH,对基体有较好的保护作用;在50℃时,B10管表面腐蚀产物为CuO、Ni和FeO,对基体的保护性较差.

采用可原位测量的管流式试验装置，利用失重和电化学阻抗谱测试对比研究了B10管在静态和动态天然海水中的腐蚀行为及其随时间的变化，并通过SEM、XPS等分析了其腐蚀形貌及腐蚀产物。结果表明，在两种海水暴露条件下，试样的腐蚀速率随时间的延长逐渐降低。B10管表面在静态下生成的腐蚀产物主要是Cu 2 O，而在动态条件下则为NiO、Cu 2 O和FeOOH，其中NiO和FeOOH的存在降低了腐蚀速率，提高了B10管的耐蚀性。本文研究表明冲刷状态有利于B10管表面形成更为致密的腐蚀产物膜，对基体起到良好的保护作用。研究结果可为海水管路动态条件下B10管成膜质量和服役性能评价提供实验依据。

Layered double hydroxides (LDHs) can serve as corrosion inhibitor reservoirs. In the present work, hydrotalcite-like LDHs were synthesized and employed as host matrixes for the release of phosphate. The morphological and structural properties of the as-prepared LDH-PO4 were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The PO43- adsorption uptake was successfully confirmed by the XRD results. The corrosion resistance of the coating with LDH-PO4 was investigated by electrochemical impedance spectroscopy (EIS), which was approximately 1 order of magnitude higher than that of the blank coating after immersion for 168 h. Results of the scanning Kelvin probe technique revealed that the potential of LDH-PO4 coating was higher and smoother than that of the blank coating after exposure to 0.5 M NaCl solution. This effect is attributed to the release of PO43- that forms a phosphate protective film in the scratched region.