Based on the survey of the application and research reports of Ti-alloy, this paper summarizes the cause and mechanism of stress corrosion cracking of Ti-alloy in deep sea environments, and discusses the effect of deep-sea environmental factors such as hydrostatic pressure, dissolved oxygen content, pH value and temperature on the stress corrosion cracking behavior. It is expected to provide a reference for the further study of stress corrosion cracking and other local corrosion types of titanium alloy, and to provide support for optimizing the microstructure and properties of Ti-alloy and the establishment of advanced Ti-alloy material for the deep sea engineering.

This article reviews the Pt modified β-(Ni,Pt)Al coating and γ-γ' type coating with nickel-based superalloy as the substrate, and focuses on the preparation process of the Pt modified aluminide coating, the variation of the coating microstructure with processing parameters, the mechanism of Pt enhancing the oxidation resistance of the aluminide coating, the effect of Al on the high temperature oxidation performance of the coating, and the degradation process of the coating in terms of element interdiffusion, phase transition, and surface undulation. Finally, the development of Pt modified aluminide coating is prospected.

As one of the Gen-IV (Generation Four Initiative) alternative reactors, molten salt reactor (MSR) has become a popular research topic again in recent years. Molten fluorides act as the nuclear fuel carrier and coolant in MSR. However, its highly corrosive to structural materials is a great barrier of the MSR development. The active dissolution of alloying elements is the main result of hot corrosion. Trace impurities, the formation of galvanic couples between different materials and temperature gradient in the molten salt system are the main driving forces of hot corrosion. The research status of hot corrosion and surface protection for structural materials in molten fluoride salts by domestic and foreign researchers are reviewed in the present article.

The galvanic corrosion behavior of TP2Y copper pipes coupled with #20 steel pipes in static and flowing 3.5% (mass fraction) NaCl solutions was numerically simulated by means of COMSOL Multiphysics software, while taking the flow field, concentration field and electrochemical dynamics process into consideration, aiming to predict the tendency of galvanic corrosion. The results showed that TP2Y pipes acted as the cathode and #20 steel pipes were the anode when TP2Y pipes were coupled with #20 steel pipes. The corrosion length of #20 steel pipes was dependent on the pipe diameter, flow rate and time. The length of the potential change of the coupled pipes increased gradually with pipe diameters, and that the inner surface potential of the coupled pipes increased with flow rate compared with that under stagnant condition. At the same time, the inner surface potentials of the copper (TP2Y) pipes and #20 steel pipes became negative and positive at the coupling position, respectively. The current density was up to the Max. at the coupling position. Under stagnant condition, the inner surface potentials of the copper (TP2Y) pipes and #20 steel pipes became negative, and did not change until 48 h later. the maximum corroded thickness at the flange of #20 steel would be up to about 8.87 μm, and the corrosion length would be about 800 mm in 30 d.

The effect of stepwise cathodic polarizations with two potentials: either -850 mV (vs. SCE) then -1050 mV or -1050 mV then -850 mV on the corrosion behavior of X65 steel in the aged Qingdao seawater inoculated with iron oxidizing bacteria was studied by means of electrochemical techniques, scanning electron microscopy and confocal laser scanning microscopy and Raman spectroscopy. The results show that both of the two stepwise polarizations all can inhibit the IOB induced corrosion. There is little difference in the composition but variation in the content of each constituent of corrosion products formed on X65 steel in the aged Qingdao seawater inoculated with iron oxidizing bacteria by open circuit potential as well as by applying either of the two stepwise polarizations respectively. The polarization by -1050 mV can inhibit IOB adhesion, but cannot completely remove the formed biofilm, which may be the reason why the stepwise polarization by -1050 mV then -850 mV has better protection effect than that by -850 mV then -1050 mV.

Four high entropy alloys of FeCrMn_1.3NiAl_x (x= 0, 0.25, 0.5, 0.75) with different Al content were smelted by vacuum magnetic suspension method. The effect of Al content on the microstructure and passivation behavior of the as-cast alloys FeCrMn_1.3NiAl_x in 0.5 mol/L H₂SO₄ solution was investigated by means of XRD, FE-SEM, SKPFM, EPMA and potentiodynamic polarization technique. The results show that the FeCrMn_1.3NiAl_x (x=0, 0.25) alloy presents a two-phase microstructure of fcc (Fe-Mn-Ni)+bcc (Fe-Cr-Mn). The Fe-Cr-Mn phase of bcc structure has higher electrochemical activity, and therewith is preferred to dissolve, which results in two obvious passivation-potential and -current peaks. As the Al addition reaches x=0.5, the fcc phase almost entirely disappeared in the alloy, therefore the alloy composed of the bcc Fe-Cr-Mn phase with uniformly distributed particles and strips of b2 phase (Al-Ni-Mn). Due to the difference in electrochemical activity of the above two phases is not much, so that, the alloy present only one passivation potential and passivation current peak. Meanwhile the new hard ρ-phase of higher electrochemical activity emerges in the alloy, which resulted in lower passivation potential and smaller passivation current density. The ρ-phase disappears for the alloy with x=0.75 Al, correspondingly, the low passivation potential peak also disappears. The addition of Al can affect the passivation behavior of FeCrMn_1.3NiAl_x high entropy alloys in 0.5 mol/L H₂SO₄ solution by changing the microstructure, composition and distribution of phases in local-areas, so as the electrochemical activity of FeCrMn_1.3NiAl_x high entropy alloys. With the increase of Al, the passivation current density of the alloy increases due to the poor passivation performance of b2 phase, which in turn reduces the passivation performance of the alloys.

Submarine pipelines are an important way for offshore oil and gas transportation. The fatigue behavior of X65 steel by applied loads of different modes was studied in air and artificial seawater by a fatigue tester. The fatigue fracture and secondary crack were observed by SEM. The results showed that in air and artificial seawater, the fatigue life of X65 steel was the longest by the applied load of positive sawtooth wave, it is the next by the load of triangular wave and it is the shortest by the load of sine wave. The fatigue life of X65 steel in the seawater was significantly reduced compared with that in air. The stress rise time by load of either sinusoidal wave or triangular wave was shorter, which was conducive to dislocation initiation and acceleration of crack initiation. By applied load of sine wave, the holding time at σ_max was the longest, the dislocation slip formed faster, and the fatigue crack propagation was the fastest. In the artificial seawater, Cl^- promoted the initiation of pitting on the surface of X65 steel, which became the initiation sites of fatigue crack. After the cracks have formed, the electrolyte entered the crevice within cracks, whilst the cracks opened and closed repeatedly under the alternating stress, resulting in rapid crack propagation. In the artificial seawater, by the applied load of positive sawtooth waveform, the corrosion fatigue crack propagation mechanism of X65 steel was anodic dissolution, while by the applied loads of sine wave and triangular wave, the corrosion fatigue crack propagation mechanism was hydrogen embrittlement and anodic dissolution. The corrosion fatigue cracking sensitivity was the highest by the applied load with sinusoidal wave.

The effect of polyethylene glycol-600 (PEG-600) on the acidic Zn-Ni alloy plating process was studied by means of cyclic voltammetry (CV) curve measurement. The influence of the concentration of polyethylene glycol-600 (PEG-600) in the acidic Zn-Ni alloy plating electrolyte on the corrosion resistance and the surface morphology of the Zn-Ni alloy coatings was characterized via electrochemical impedance spectroscopy (EIS), Taffel polarization curve measurement and surface morphology analysis method. The results show that PEG-600, as a non-ionic surfactant, has a strong adsorption capacity on the surface of cathode. The addition of PEG-600 to the plating electrolyte will affect the electroplating process of the Zn-Ni alloy, making it more difficult for Zn²⁺ and Ni²⁺ to move to the surface of the cathode, as a result, the co-deposition peak position of Zn-Ni may move towards negative potential direction, so that the cathode overpotential rises. With the increase of the concentration of PEG-600 in the plating electrolyte, the corrosion resistance of the electroplated Zn-Ni alloy coating increases first and then decreases. When the concentration of PEG-600 is 3.33×10^-2 mol/L, the corrosion resistance of the electroplated Zn-Ni alloy coating reaches the best, namely the coating with electrochemical impedance of 1960 Ω·cm² and free-corrosion current of 1.97×10^-5 A·cm^-2, and the Zn-Ni alloy coating consists of uniformly intermetallic compound γ phase with better surface morphology in micro scale.

MCrAlY coatings are widely used for various parts of high-temperature alloy to enhance their corrosion resistance at high temperatures. However, there still exist unavoidable defects within the as-prepared coating, as well as at the interface coating/substrate, which promotes the initiation of cracking and failure of the coating during service at high temperature, and ultimately limits the service life of the alloy components. In this study, NiCoCrAlY coating was deposited on K417G high temperature alloy by arc ion plating, and the coated alloy samples was vacuum heat treated at 950, 1000 and 1050 ℃ respectively for 4 h. Further, the oxidation behavior of the heat-treated samples were assessed isothermally at 1000 ℃ in air for a long term so that to examine the effectiveness of vacuum heat treatment. Finally, the surface and cross-sectional morphology and phase composition of the oxidized coating/alloy were characterized by means of XRD, SEM with EDS. The results show that after vacuum heat treatment the plated NiCoCrAlY coating is tightly bonded to the substrate alloy, the oxidation mass gain of the coatings is relatively slow, and a uniform and dense oxide scale can form on their surface. Among others, the sample after heat-treated at 1000°C provides the best performance, which exhibits better resistance to scale spallation with lower mass gain.

The cyclic oxidation performance of the direct-sintered SiC was assessed in air at 1300 ℃ with cyclic period of 5 h, and at 1400 ℃ with cyclic period of 1, 3 and 5 h, respectively, meanwhile, the mass change of the sintered SiC vs cycle nunber was measured with analytical balance. Then the morphology evolution and the formed oxide scales of the direct-sintered SiC were characterized by scanning electron microscope. The results indicate that during the cyclic oxidation, the direct-sintered SiC experienced a two-stage process, i.e. in the early stage the sintered SiC presented a course of parabolic mass gain and then turned to a course of mass loss companied by spallation of oxide scale for long-term oxidation. With the increase of cyclic oxidation temperature, the oxidation rate of direct-sintered SiC increases and the mass loss stage emerges more quickly. The shorter the cyclic period is, the easier the spallation of oxide scale takes place, and the cracking and spallation of oxide scale exerts a more serious influence on the cyclic oxidation process. As the increase of cyclic period, the occurrence of cracking and spallation of oxide scale may be postponed, but in that case, the overall spallation of oxide scale seems easy to take place.

Two cerium ion modified SiO₂ films were prepared on X80 steel by sol-gel method and electrodeposition method respectively, and the corrosion behavior of the two films in 20 MPa, 3.5%NaCl solution was studied. The corrosion behavior of the coated steel was assessed via a high-temperature and high-pressure electrochemical reactor with open circuit potential measurement, polarization curve measurement and electrochemical impedance spectroscopy. Before and after corrosion test, the coated steels were characterized by means of scanning electron microscope, energy disperse spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and contact angle tester. The results show that the corrosion resistance of the films prepared by the two methods reduced in the artificial deep sea environment, especially the electrodeposited film; after immersion in 20 MPa deionized water, no obvious cracks appeared on the two films; however, after immersion in 20 MPa salt water, a few cracks emerged on the electrodeposited film, while the sol-gel film was still relatively intact; after potentiostatic polarization in 20 MPa salt water, significant cracking and peeling off could be observed for the electrodeposition film, but only cracking could be seen for the sol-gel film; both films are hydrophilic before corrosion, but the contact angle increases significantly after corrosion, showing hydrophobicity to certain extent.

A novel ZIF-8/TiO₂ nanocomposite material was prepared via stepwise growth method to deposit ZIF-8 nanoparticles on TiO₂ nanotube arrays aiming to further optimize the photogeneration cathodic protection performance of TiO₂ photoanode so that to improve its photoelectric conversion efficiency. The structure, morphology and light response of the prepared materials were characterized by XRD, SEM and UV-vis DRS, and the photochemical test of the materials was carried out in conditions of visible light on and off. The results show that the light absorption ability of ZIF-8/TiO₂ nanocomposite material was extended into the visible region, and the cathodic protection potential of ZIF-8/TiO₂ nanocomposite can be reduced to -0.92 V in condition of light on when coupled with 304 stainless steel as the photoanode, which is about 180 mV lower than that of the simple TiO₂ nanotube array, and it shows excellent photogenerated cathodic protection performance for 304 stainless steel for long time.

The pitting corrosion behavior of ultra-fine lamellated (UFL) Al-4%Cu alloy prepared by cold rolling at room temperature has been studied by means of scanning electron microscope (SEM), transmission electron microscope (TEM), microhardness tester and potentiodynamic polarization measurement aiming to understand the effect of element segregation and precipitates at grain boundaries on pitting corrosion potential. The result shows that the average lamellar spacing of cold rolled Al-Cu alloy is 159 nm and there exists obvious segregation of Cu at boundaries. The pitting corrosion potential of the cold rolled Al-Cu is found to be similar to that of the coarse grain ones. After aging treatment, the pitting corrosion potential decreases obviously because of precipitation of second phases at grain boundaries. These results indicate that the element segregation at grain boundaries has no significant effect on the pitting corrosion behavior of Al-Cu alloy, while the precipitation of second phases rich in Cu can have an obvious effect on the pitting corrosion behavior.

Surface treatments of titanium-zirconium conversion and hot-dip galvanization were applied on 6016 Al-alloy and DC01 carbon steel, respectively. Then the galvanic corrosion behavior in 5% NaCl solution for the couple of 6016 Al-alloy and DC01 carbon steel without and with pre-surface treatment was comparatively studied by means of polarization measurement , electrochemical noise measurement and scanning electron microscope (SEM). The results showed that the galvanic corrosion between the bare 6016 Al-alloy and bare DC01 carbon steel was severe. The merely titanium-zirconium conversion treatment on 6016 Al-alloy cannot solve the problem of galvanic corrosion of the couple of the surface treated 6016 Al-alloy with bare DC01 carbon steel, while the treated 6016 Al-alloy suffered from pitting corrosion. However, for the couple of bare 6016 Al-alloy and the galvanized steel, the former one could become a cathode, which can be protected by the galvanized steel, whereas, the iron-rich inclusions on 6016 Al-alloy surface induced the formation of pits. However, the galvanic current can be reduced by two orders for the couple of the galvanized DC01 steel and the titanium-zirconium conversion treated 6016 Al-alloy.

Waste incinerators are faced with many high-temperature corrosion problems because they work at high temperatures all year round. The NaCl induced hot corrosion behavior of three novel austenitic stainless steels 254SMo, 904L and 317L in NaCl salt at 750, 850 and 950 ℃ was studied in order to simulate the corrosion emerged on the fire side of tubes in waste incinerator by means of corrosion kinetic measurement, SEM/EDS and XRD. The results show that the three austenitic stainless steels show mass loss during the hot corrosion process, their corrosion resistance may be ranked as follows: 254SMo stainless steel ＞904L stainless steel ＞317L stainless steel, whilst their mass loss increases with the increase of temperature and time. The addition of Mo can alleviate the corrosion of the steels in the chloride salt. Serious intergranular corrosion occurred in the three austenitic stainless steels at 850 and 950 ℃. The hot corrosion reaction follows the so called “active oxidation” mechanism, and the generated chlorine gas will participate in the reaction cycle.

Dissimilar metal welded joints of 2507 super duplex stainless steel (2507SDSS/X80) were prepared via metal inert gas welding (MIG) technology with 2507SDSS and X80 pipeline steel as raw and processed materials. The microstructure and properties of dissimilar metal welded joints were assessed by means of optical microscopy, SEM with EDS and microhardness tester, as well as electrochemical test in artificial seawater. Results show that obvious concentration gradients of Fe, Cr, Ni, Mo and Mn could be detected in the area between the fusion line and Type-II interface. The dilution zone has the highest hardness. Galvanic corrosion emerges for the couple of X80 steel and weld metal. In general, MIG welding filler ER2594 is suitable for welding the dissimilar metals of 2507SDSS super duplex stainless steel and low alloy in practical application.

The hydrophobic surface film on AM60 Mg-alloy was prepared by chemical etching, and then soaking in stearic acid ethanol solution. The microstructure, hydrophobic properties and corrosion resistance of hydrophobic surface were characterized by means of scanning electron microscope, contact angle tester and electrochemical workstation. The results showed that the AM60 Mg-alloy was super hydrophilic after etching with hydrochloric acid. When the etching time was 25 min, the contact angle reached a maximum value, which was 125% higher than that of the untreated surface. With the increase of soaking time in the stearic acid ethanol solution, the contact angle increases first and then decreases. When soaked for 12 h, the contact angle reaches the maximum of 150.18° and the rolling angle is less than 10°. At this time, the hydrophobic film presents a micro/nano rough surface with low-surface energy, which have superior hydrophobic properties. The hydrophobic AM60 Mg-alloy has good corrosion resistance, and its corrosion current density is 88.19% lower than that of untreated matrix material, and the corresponding corrosion voltage is 19.72% higher, which significantly improves the corrosion resistance of the AM60 Mg-alloy. At the same time, the treated AM60 Mg-alloy has also good self-cleaning performance to dust and aqueous solution.

Organic coatings are commonly used as an effective strategy for protecting carbon steel from corrosion, but the traditional organic coatings are susceptible to generate micron cracks or defects during service, resulting in the premature failure. In view of this problem, a novel benzotriazole containing nanocontainers, namely BTA@MSNs-SO₃H-PDDA with pH-sensitivity was prepared firstly, then a BTA@MSNs-SO₃H-PDDA doped smart organic coating was fabricated for application on carbon steel. The structure and performance of BTA@MSNs-SO₃H-PDDA were characterized by scanning electron microscopy (SEM), dynamic light scattering analysis (DLS), X-ray diffraction analysis (XRD), infrared spectroscopy (FT-IR), thermogravimetry (TGA) and ultraviolet-visible spectroscopy (UV-Vis). The protective performance of the smart coatings for carbon steel was evaluated by electrochemical impedance spectroscopy and salt spray accelerated tests. The results showed that the particles of BTA@MSNs-SO₃H-PDDA are near-spherical in shape, with an average diameter of 718 nm. The amount of BTA loaded in BTA@MSNs-SO₃H-PDDA is about 13.37%. The releasing rate of BTA from BTA@MSNs-SO₃H- PDDA can be accelerated via the sensitive response of the pH changes. The prepared smart coating based on BTA@MSNs-SO₃H-PDDA presents remarkable anti-corrosion performance for carbon steel.

The microstructure, composition and electrochemical corrosion properties of the oxidation-induced transition layer on austenitic steel Fe32Mn7Cr3Al2Si was investigated by means of XRD, EPMA, anode polarization and electrochemical impedance measurement, respectively. The Fe32Mn7Cr3Al2Si austenitic steel was intentionally oxidized at 700 and 800 ℃ in air, respectively, the formed oxide scale was typically composed of Mn₂O₃ outer sublayer, Mn₂SiO₄ middle sublayer, and Al₂O₃ inner sublayer. A transition layer of α-ferrite with Mn-depletion of 11% and Cr-enrichment of 14% at the interface of oxide scale/steel matrix was occurred at 800 ℃ in air for 160 h. Compared with the original Fe32Mn7Cr3Al2Si austenitic steel, the transition layer exhibited an increased passivation ability in 1 mol/L Na₂SO₄ solution, correspondingly, the free-corrosion potential increased from -463 mV (SCE) to 248 mV (SCE), the free corrosion current density decreased from the 2.8 μA/cm² to 0.4 μA/cm², and the resistant R_t increased from 15.5 kΩ·cm² to 69.7 kΩ·cm². It follows that Al- and Si-alloying can promote the Cr enrichment in the Mn depletion layer and therefore, improve the corrosion resistance of Fe32Mn7Cr3Al2Si austenitic steel.

Novel chromium-free zinc-aluminum coatings with different content of multi-walled carbon nanotubes (MWCNTs) were prepared by ultrasonic dispersion method. The effect of MWCNTs on the morphology, composition, adhesion and corrosion resistance of chromium-free zinc aluminum coatings were investigated by means of scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) and adhesion tester as well as immersion test in 3.5%NaCl solution with electrochemical impedance spectroscopy and polarization curve measurement. Results show that when the MWCNTs content was 0%~0.7%, the coatings were smooth flat and dense, the flaky zinc powders and aluminum powders were parallel to the substrate, providing a good physical shielding. When the MWCNTs content was 0.3%, the coating had the best adhesion and showed the best corrosion resistance in NaCl solution, its free-corrosion current was 2.019×10^-5 A/cm², and impedance modulus reached 10³ Ω·cm². In addition, the mechanism of MWCNTs affecting the corrosion resistance of the coating was explored.

Aiming at the problem related with serious corrosion and large economic loss of embedded monitoring instruments or sensors in different underground environments, the corrosion behavior of shell material (316L stainless steel) of embedded monitoring sensors in acid- and brine-containing simulated environments of tailings ponds were studied by means of coupon immersion with mass loss method, electrochemical measurement and scanning electron microscopy (SEM). The results show that in the acid containing artificial solution of pH1.5, the passive film is gradually formed on the 316 SS surface in a short period of time, and the corrosion resistance is getting better and better. However, the corrosion resistance of the 316SS is slightly reduced after a long-term immersion corrosion. In the artificial solution containing mixed sulfuric acid and brine of pH3, and that containing brine of pH7.5 respecyively, the corrosion resistance of the 316SS is better in the short term The existence of corrosive Cl^- in brine accelerated the dissolution and destruction of the passive film, and the corrosion resistance decreased significantly.

In an experiment tank of simulated tidal zone, the variation of corrosion behavior of X60 pipeline steel with the tidal water fluctuations at different monitoring positions was characterized by means of corrosion morphology observation, corrosion product analysis, and in-situ open-circuit potential monitoring. The results show that the corrosion behavior of pipeline steel is different at different positions in tidal zone. The corrosion rate in the middle and low tide areas is faster than that in the highest and lowest tide areas. With the decrease of tidal level, the open circuit potential decreases continuously. The cathodic process in the highest tide zone is mainly controlled by oxygen reduction. The cathodic process in the middle and low tide zone is controlled by rust reduction during high tide, and it is controlled by oxygen reduction during ebb tide. The change process of open-circuit potential in the lowest tide zone has nothing to do with tide fluctuation.