Bronze relics are precious historical and cultural heritage of mankind, as the bearer of important historical information about the human civilization, but their corrosion-prone characteristics make them face a serious threat of rust and eventually fester. Studying the corrosion and destruction behavior of bronzes and correspondingly adopting effective sealing technologies can not only protect the long-term inheritance of bronzes, but also retain their historical research and artistic appreciation value. At present, the research on the corrosion behavior and sealing technologies of bronzes is still lacking in system. There are still many scientific and technical problems that need to be solved urgently in the effect of multi-factor synergistic competition on the evolution characteristics of bronze rust layers in the state of being buried or stored, the diagnostic methods and quantitative standards of bronze diseases, the sealing technologies of bronzes and the construction of databases related to bronze corrosion and sealing. This paper focuses on the key scientific issues in the whole process of bronze excavation, extraction, storage and protection, reviews the current main research results in the field of bronze corrosion behavior and sealing technologies, and the corrosion mechanism of bronzes. The influences of inherent factors related with bronze such as chemical composition and microstructure, as well as the external environmental factors such as Cl- concentration, humidity and temperature on the corrosion behavior of bronze are outlined. The existing methods for the diagnosis and classification of bronzes are analyzed, and the existing temporary and long-term sealing technologies for bronzes are summarized. At last, the future development trend of bronze corrosion and sealing is prospected in this paper, and we hope to guide and promote the development of bronze corrosion and sealing technology by constructing a comprehensive standard database of environment-bronze-diseases-sealing technologies.
Stress corrosion cracking (SCC) is one of the failure models of ultra-high strength steels for aircraft landing gear. This paper sums up the development history of ultra-high strength steels first, followed by a brief introduction of the mechanism and model of SCC. The test methods of SCC and the characterization of hydrogen were also summarized. Key factors affecting the SCC of ultra-high strength steels, such as the alloy composition, microstructure, stress and environment were discussed thoroughly. Finally, trends and challenges in the research of SCC for aircraft landing gear steels were briefly addressed.
As one of the main means to inhibit atmospheric corrosion of metal, vapor phase inhibitor is more and more widely used because of its excellent corrosion preventive effect, higher cost performance and easy to use. The development of analytical methods for vapor phase inhibitors has important guiding significance for the mechanism research and development of new vapor phase inhibitors. This paper introduces the classification of two kinds of vapor phase inhibitor, and describes the characteristics, such as volatility, solubility, adsorption and corrosion inhibition of vapor phase inhibitor. In order to test the different properties of vapor phase inhibitors, several analytical methods were introduced. The volatility test is measured in terms of saturated vapor pressure. Due to the advantages of simple operation and intuitive results, mass loss analysis is widely used in the detection of vapor phase inhibitors and to verify the accuracy of other methods. Electrochemical measurements can reveal a lot of features related to the action of vapor phase corrosion inhibitors, has become the mainstream method. Surface morphological techniques can further explore the film forming mechanism of corrosion inhibitor on metal surface. In sum, the current analysis methods of vapor phase inhibitors are summarized, and the future development trend of vapor phase inhibitor analysis methods is prospected.
In order to achieve the goals of the “peak carbon dioxide emission and carbon neutrality”, it is essential to develop hydrogen energy. During the production, transportation, storage and use of hydrogen, hydrogen permeation is easy to occur and causes hydrogen damage to metal materials, which not only shortens the service life of pipelines and equipment, but also brings serious potential safety hazards. So it is of great significance to promote the development of permeated hydrogen detection techniques. Permeated hydrogen testing technology can be divided into indoor- and field-permeated hydrogen testing techniques. The indoor permeated hydrogen testing techniques include current method, hot/melt extraction, thermal desorption spectroscopy (TDS), hydrogen micro-contact printing (HMP), scanning Kelvin probe force microscopy (SKPFM), secondary ion mass spectroscopy (SIMS), atom probe tomography (APT) and neutron radiography (NRG). The field permeated hydrogen testing techniques include hydrogenochromic method, hydrogen flux method, hydrogen probe method, hydrogen sensor, as well as field Kelvin probe (FKP) technique. For the indoor testing, the principles and characteristics of several detection techniques were summarized and applicable scope was also introduced. The current method, hot/melt extraction and TDS are used to measure the average hydrogen concentration in materials, but none of the above methods have the ability of spatial resolution. The silver particles produced by the substitution reaction between Ag+ and H by HMP reflect the distribution and diffusion path of hydrogen, but it is not certain whether Fe participates in that. By continuously detecting the potential of a certain position, SKPFM can reveal the hydrogen enrichment and the dynamic process of diffusion in a specific position. However, when current/potential is applied on the sample surface, it will disturb the test results. Both SIMS and APT technology rely on mass spectrometry, and have spatial resolution but their measuring chamber need to be filled with deuterium to eliminate the influence of background hydrogen. NRG can judge the concentration and distribution of hydrogen by detecting the hydrogen intensity and bright area, but its spatial resolution can only reach micron level. For the field testing, the parameters of several testing equipment provided on the market are investigated in this article, while the principle, application scope, advantages and disadvantages of each method are also summarized. Finally, some suggestions are put forward for the future development of hydrogen permeation detection methods.
As a candidate of Generation IV fast reactors, Lead Fast Reactors (LFRs) have attracted global research interests for past decades. Liquid lead and lead-bismuth eutectic (LBE) are both proposed as the coolants for LFRs due to their favorable transmutation and breeding capability. However, the direct exposure to heavy liquid metals can lead to premature failures of the structural steels, such as liquid metal corrosion and liquid metal embrittlement. It has been widely proven that the corrosion performance of structural steels all depends on various environment parameters such as ambient temperature, the dissolved oxygen concentration in liquid metals, liquid flow pattern, and the co-existing irradiation. For the latter cases, liquid metal corrosion can therefore be generalized to erosion-assisted mechanical failure and irradiation damage. Here we reviewed the research progress on liquid metal corrosion issues theoretically and experimentally for LFRs. The progress can be categorized into following aspects: (1) microscopic liquid metal corrosion mechanism revealed by advanced material characterization methods as well as density functional theory, (2) development of anti-corrosion materials and surface modification techniques, (3) design of dynamic corrosion apparatus to investigate erosion-corrosion synergy in flowing liquid metals and long-term corrosion prediction modelling concerning primarily with liquid Pb/LBE loops, (4) introduction of various in-situ irradiation sources (i.e. neutrons, heavy ions and protons) to the liquid Pb/LBE corrosion apparatus to investigate the irradiation-corrosion synergistic effects.
Firstly, the mechanism of CO2 induced corrosion of submarine pipeline is introduced, including chemical reaction process, electrochemical reaction process, mass transfer process and film formation process. Secondly, the influencing factors of CO2 induced corrosion of submarine pipelines are summarized, which mainly include material factors determined by chemical composition and microstructure, and external environmental factors determined by medium composition, temperature and pH, etc. At the same time, the empirical/semi-empirical regulations of the corrosion rate versus influencing factors are summarized. Finally, the models of CO2 induced corrosion of submarine pipeline is summarized, and the control steps and boundary conditions of the principle model and empirical model for corrosion-assessment and -prediction are introduced in detail.
How to avoid metal corrosion has became a key issure due to the widespread applications of various metals, therefore, it is urgent to develop the low toxicity and high-efficiency anticorrosive materials. Carbon dots (CDs), as a new zero-dimensional member of the carbon family, possesses the advantages of strong adsorption capacity, low toxicity, high solubility, good stability, and abundant surface functional groups, attract extensive attentions of researchers in the field of corrosion and protection of metallic materials. Herein, this work systematically elaborates the research progress of carbon dots especially as water-phase corrosion inhibitors and coating fillers. This review introduces corrosion inhibition effect about different heteroatom-doped carbon dots (nitrogen doped carbon dots, cerium and nitrogen co-doped carbon dots and nitrogen and sulfur co-doped carbon dots) on various metals. The corresponding corrosion inhibition mechanism can be summarized as that the protective film is formed through adsorption of CDs (physical adsorption or chemical adsorption) on surface of metals. Furthermore, we summarize the anti-corrosion mechanisms and research achievements of carbon dots as solvent-based and water-based coating fillers. By virtue of its small size and plentiful of functional groups, CDs can fill into micropores and fix the defects of coating so that to improve the comprehensive anti-corrosion performances of the composite coating. Finally, the challenges that carbon dots face in the field of corrosion and protection are also discussed.
Friction stir welding, as a solid state bonding process, can effectively solve the welding problems of 2xxx series Al-alloy in engineering applications. However, during friction stir welding process, every local area of the welded joint has experienced distinctive thermal cycling and material plastic flow, therefore, different local areas may exhibit obviously differences in their microstructure evolution, as well as in corrosion behavior and corrosion mechanism. In this paper, the corrosion types, positions of corrosion initiation and relevant inducing factors for friction stir welded joints of 2xxx series Al-alloy were reviewed, meanwhile, the relevant corrosion mechanism of weld joints and corresponding methods of improving corrosion resistance for the welded joints were also summerized.
Mg-Li alloys with high specific strength and stiffness are ideal metal structural engineering materials for aerospace due to their excellent weight reduction effect. However, their poor corrosion resistance severely limits the wide application in some service environments. Therefore, in order to meet the demand of application, it is still necessary to adjust and optimize the composition of corrosion resistant Mg-Li alloys and improve its preparation process in the future. The research status on corrosion mechanism and different types of surface protection methods (metallic coating, anodic oxidation, conductive-shielded polymer coating, and smart coating), as well as future applications of corrosion-resistant Mg-Li alloys were summarized in this paper. Meanwhile, the advantages and limitation of different types of corrosion protection methods were analyzed, and the future research directions of corrosion and protection for corrosion resistant Mg-Li alloys are discussed so that to provide new ideas for future development of higher corrosion-resistant Mg-Li alloys.
The ion selective electrode technology (ISET) based on scanning electrochemical microscopy (SECM) enables in situ monitoring of non-electrochemically active substances at both micron and submicron scales of the metal/solution interface. However, the research on the stability, potential response time, and anti-ion interference ability of ISET is obviously insufficient. In this paper, an all-solid platinum/iridium oxide (Pt/IrO x ) electrochemical microsensor with pH response was prepared by deposing an iridium oxide thin film on the surface of a 10 μm diameter platinum ultra-microelectrode. Its linear response, instantaneous potential response, stability and anti-ion interference ability were analyzed. The results showed that the prepared Pt/IrO x -pH microsensor electrode exhibited excellent linear response performance in the range of pH=1.00-13.00 (R2=0.999) and high stability in both the short term (within 20000 s) and the long term (within 110 d). When the pH value of the solution changed, the potential of the Pt/IrO x -pH microsensor could change instantaneously, namely the sensor responds quickly to the solution pH value. Moreover, after adding Fe2+, Cu2+ and Cl- into the solution, the linear response and stability of the sensor remain unchanged with high anti-interference ability. However, the addition of Ti3+ could affect the accuracy of the microsensor detection. The prepared Pt/IrO x -pH microsensor was further applied to investigate the galvanic corrosion of copper and 304 stainless steel in 3.5% NaCl solution with pH=2.00. The results of SECM surface and line scanning images combined with OCP results showed that when the galvanic corrosion of Cu and 304 stainless steel began, Cu acted as the cathode and 304 stainless steel was the anode. However, after 12 h immersion, the polarity of anode and cathode was reversed, that is, Cu was the anode and 304 stainless steel was the cathode, and the surface pH value of Cu was lower.
Intergranular corrosion is an important form of failure of austenitic stainless steels such as 316L, and the precipitation of M23C6 and the formation of Cr-poor zones are usually considered to be an important cause of intergranular corrosion. Selected laser melting (SLM) is an emerging metal additive manufacturing technology, and the SLM process of 316L stainless steel has gradually matured in recent years. The rapid condensation of the laser melt pool during SLM processing leads to the existence of sub-grain boundaries, high-density dislocations and other non-equilibrium structures inside the SLM processed 316L stainless steel (later referred to as SLM-316L stainless steel), and the post-heat treatment is used to SLM-316L stainless steel by post-treatment to optimize the organization of the SLM-316L stainless steel can obtain a better overall performance. However, there are few reports on the intergranular corrosion of SLM-316L stainless steel, and the mechanism of the original non-equilibrium structure and post-treatment on the precipitation of M23C6 and the formation of the Cr-depleted zone is not clear. In this paper, two SLM-316L stainless steels with different carbon contents were selected as the object of study, and the thermodynamic parameters of precipitated phases such as M23C6 were obtained by using Thermal-calc software with the composition of 316L stainless steel with different carbon contents as input parameters. Based on this, SLM-316L stainless steel was subjected to 900 ºC post-heat treatment and 650 ºC sensitization treatment. Subsequently, SEM, TEM and SKPFM were used to study the characteristics of the organization and precipitation phases of SLM-316L stainless steel, and the intergranular corrosion behavior of SLM-316L stainless steel was studied by DL-EPR and ammonium persulfate electrolysis. The results showed that sub-grain and dislocation started to disappear after heat treatment at 900 ºC, and discontinuous micron-sized M23C6 precipitated at the grain boundaries of SLM-316L stainless steel with higher carbon content (0.0090%), while no M23C6 precipitated in the specimen with lower carbon content (0.0063%), the intergranular corrosion resistance of SLM-316L with lower carbon content was higher than that of SLM-316L. The intergranular corrosion resistance of SLM-316L with lower carbon content is higher than that of the specimen with higher carbon content, and the intergranular corrosion resistance of SLM-316L stainless steel with both carbon contents decreases after 900 ºC post heat treatment; the intergranular corrosion of SLM-316L stainless steel after heat treatment at 900 ºC originates mainly in the Cr-poor zone around micron-sized M23C6, followed by the formation of corrosion pits and gouges around the M23C6 precipitation phase and along the grain boundary diffusion, respectively.
The oxidation behavior of quaternary (Cr2/3Ti1/3)3AlC2 MAX ceramic at high temperatures in air and steam was investigated by isothermal oxidation test. The good oxidation resistance of (Cr2/3Ti1/3)3AlC2 at 800-1200 ℃ in air and at 1000-1200 ℃ in steam may be ascribed to the oxide scale with Al2O3, TiO2 and Cr2O3 formed on the surface of (Cr2/3Ti1/3)3AlC2 during oxidation. An oxide scale with external Ti-rich layer, intermediate Cr-rich layer and internal Al-rich layer was formed on the surface of (Cr2/3Ti1/3)3AlC2 during oxidation at 1200 ℃ in air/steam. The structure of the oxide scale was affected by the selective oxidation and diffusion of elements in (Cr2/3Ti1/3)3AlC2. The results indicate that (Cr2/3Ti1/3)3AlC2 exhibit good oxidation resistance in high temperature air/steam.
The effect of ultrasonic shot peening (USSP) on microstructure, microhardness, electrochemical corrosion and intergranular corrosion behavior of a 7075 Al-alloy rod were investigated by means of optical microscopy (OM), X-ray diffraction (XRD), transmission electron microscope (TEM) and corrosion tests.Results showed that after USSP treatment, gradient nanostructures were obtained in the topmost layer with grain size of ~78.2 nm; the precipitated strengthening phases (η and η′ phase) of surface region redissolved into Al matrix, and the hardness of surface layer increased by about 20%. Results of polarization test in 0.1 mol/L Na2SO4+20 mmol/L NaCl solution showed that pitting potential of the alloy shifted to the positive directipn position after USSP, implying a better resistance against pitting corrosion initiation. Electrochemical corrosion tests in 3.5%NaCl solution indicated that a higher corrosion rate of 7075 Al-alloy was obtained after USSP treatment. In addition, the corrosion rate showed a decreasing trend as a function of peened sample depth. Intergranular corrosion immersion tests showed that the resistance to intergranular corrosion of AA7075 decreased after USSP treatment. Combined with the microstructure characterization results, the surface strengthening mechanism and corrosion mechanism of ultrasonic shot peened 7075 Al-alloy were discussed.
In order to understand the adaptability and failure mechanism of landing gear materials for amphibious aircraft in marine environment, the failure behavior of A100 ultra-high strength steel beneath an unsteady thin electrolyte layer (TEL) and in artificial seawater (ASW) was studied via immersion test, slow strain rate tensile test and electrochemical measurements. The results show that in comparison with the test in ASW, the charge transfer resistance of A100 steel beneath TEL is significantly reduced, correspondingly, the steel corrosion is significantly promoted, and the deposition of corrosion products is more obvious. Due to the existence of TEL, the oxygen reduction process and the deposition of corrosion products was all promoted. Meanwhile, the corrosion process under the dynamic TEL was stimulated due to the presence of reduction reaction of the Fe3+ within the corrosion products accompanied with the efficient dissolved oxygen, which then resulted in the occurrence of obvious uniform corrosion beneath the corrosion products. Similarly, A100 steel is more sensitive to stress corrosion cracking (SCC), when the test steel is covered with TEL, because the accelerating corrosion process may lead to the decreases of the effective bearing cross-sectional area of A100 steel. At the same time, the acidification process beneath the corrosion product layer promotes the hydrogen precipitation reaction and accelerates the SCC reaction process. It follows that the significant increase of the sensitivity of SCC for A100 steel may be ascribed to both the strength loss and elongation loss during the SCC testing in TEL environment.
1Cr18Ni9Ti is brazed with BNi-2 thin strip filler metal. The microstructure, electrochemical characteristics, and hardness and tensile properties of the joint are assessed. While the evolution of the microstructure and mechanical properties of the joint is examined after salt spray corrosion test. The results show that the 1Cr18Ni9Ti brazed joint is well formed, and the microhardness of the weld is significantly higher than that of the base metal on both sides. The tensile strength of the welded joint reaches 500 MPa. The corrosion potential of the weld seam is higher than that of 1Cr18Ni9Ti base metal, and thus the joint is subject to galvanic corrosion in the salt spray environment. The observation results show that the fracture of the uncorroded brazed joint occurs at the adjacent base metal, and the fracture analysis shows that during tensile process, cracks may firstly initiate at the brazing solder, and then cracks propagate to the base metal, and finally fracture occurs. The fractured surface exhibits obvious features of plastic deformation. After salt spray corrosion test, the mechanical properties of the 1Cr18Ni9Ti brazed joint decreased, and the fracture occurred at the interface of brazed joint/base metal after the tensile test, but without characteristics of plastic deformation.
The work aims to improve the stability and mechanical wear resistance of the lubricating layer of the slippery coating, which are the key problems to be solved for long-term service of the coating. The SiO2 with coral cluster morphology was prepared by water-oil two-phase method, and then porous micro-nanostructures were constructed by mixing SiO2 with acrylic polyurethane resin and spraying. Meanwhile the influence of substrate morphology with different SiO2 content on the storage capacity of dimethyl silicone oil of the coating surface was studied. The mechanical abrasion resistance, self-cleaning and anti-corrosion properties of the slippery coatings were also assessed. The results showed that with the increased of SiO2 content, the roughness of the substrate increased, and the disordered substrate morphology was more uniform, which was more conducive to improving the stability of the silicon oil layer. The sliding angle of SiO2-25 was 5.4°. And the SiO2-25 even had excellent lyophobicity and self-cleaning property after wear test. Due to the influence of fillers on the pore structure of the coating, the |Z|0.01 Hz of SiO2-25 was still as high as 6.62×109 Ω·cm2 after 20 d of immersion in 3.5%NaCl solution, higher than SiO2-30. Among others, the coating of SiO2-25 has the best corrosion resistance for carbon steel for the long-term.
The corrosion behavior of B10 Cu-Ni alloy pipe in natural seawater at different temperatures was investigated via pipe flow test device capable of in-situ measurement designed independently by means of electrochemical impedance spectroscope (EIS) and other electrochemical methods, and the corrosion morphology and corrosion products composition were analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). The results indicated that the corrosion product film on the surface of B10 pipe became denser with the decrease of temperature in the range of 10-50 ℃, leading to the increase of corrosion resistance of the film and the decrease of corrosion rate of the alloy. The corrosion behavior of B10 pipe in seawater would change with time and temperature. At 10, 25 and 35 ℃, the corrosion rate of B10 pipe gradually decreased with the extension of time, and the corrosion products were mainly Cu2O, NiO and FeOOH, resulting in a better protective effect to the matrix. At 50 ℃, the corrosion products on the surface of B10 pipe were CuO, Ni and FeO, which presented poor protective effect to the substrate.
Valve is one of the most important components for seawater pipeline, and is widely used in ship, but it suffers from serious corrosion, which leads to leaking or unclosing. Galvanic corrosion between ZCuSn5Pb5Zn5 and B10 is the main cause of such corrosion. In this paper, the galvanic corrosion of the couple ZCuSn5Pb5Zn5/B10 in flowing seawater and the galvanic corrosion mechanism is assessed by means of electrochemical method, SEM and EDS. The results suggest that, in static seawater, the galvanic corrosion rate between ZCuSn5Pb5Zn5 and B10 is very small, the relevant anode and cathode are reversed many times. In flowing seawater of 1, 3 and 5 m/s, the galvanic corrosion rate of ZCuSn5Pb5Zn5 obviously increases, which is 22, 49 and 69 times of that in static seawater respectively. In flowing seawater, the diffusion rate of dissolved oxygen and corrosion products is accelerated and the relevant anodic- and cathodic-reactions are both accelerated, thus the galvanic corrosion rate increases. The galvanic corrosion between ZCuSn5Pb5Zn5 and B10 is controlled by both the ZCuSn5Pb5Zn5 anodic reaction and the B10 cathodic reaction. With the gradually depositions of corrosion products, the anodic- and cathodic-reactions are inhibited, however when the flowing rate is more than 3 m/s, the deposition of corrosion products turns to be difficult, thus cannot provide proper barrier effect to the galvanic corrosion.
Ferritic-martensitic steel P92 was themally aged at 800 °C for 200 and 400 h, respectively. Then corrosion behavior of the aged P92 steels was investigated in supercritical water at 600 °C, 25 MPa up to 1500 h. The microstructure, oxidation kinetics of the steels, morphology and phase composition of oxide scales were characterized by means of SEM, TEM and XRD. The results indicate that after thermal ageing at 800 ℃, the P92 steel presented microstructure composed of coarsened martensitic lath, Ostwald ripening of M23C6 carbides and sub-grains. Furthermore, the oxidation kinetics curves of the aged P92 steels at 600 ℃ are between parabolic and cubic curves, while the weight gain increased with the increasing ageing time. The oxide scales are composed of Fe3O4, (Fe,Cr)3O4 and Cr2O3. It is also discovered that there is more cracks on oxide scales of the aged steels, which led to spallation of oxide scales, whereas no signs of spallation were found on the not aged steel.
To investigate the course of fatigue damage evolution and fatigue life of the corroded steel wire with double corrosion pits for suspension bridges, a model of high-strength steel wire with double corrosion pits was established through finite element software ANSYS. Based on continuum damage mechanics combined with the time-history data of sling stress of suspenders acquired from the wind-traffic-bridge coupling vibration analysis, the course of fatigue damage evolution for the high-strength steel wire with double corrosion pits under different operation conditions was studied. Meanwhile, the influence of wind speed, traffic load, suspender position, shape of corrosion pit and shape of asymmetric double corrosion pits on the course of damage evolution and fatigue life of the high-strength steel wire with double corrosion pits was discussed respectively. The results show that the corrosion fatigue life of the steel wire with double corrosion pits is more sensitive to high wind speed rather than low wind speed. Moreover, the corrosion fatigue life of steel wire decreases with the increase of the traffic flow under the same wind speed. When the wind and traffic flow are coupled, the corrosion fatigue life of high-strength steel wire with double corrosion pits is obviously lower than that without traffic flow. The short suspender at the bridge mid-span has shorter corrosion fatigue life than that of the longest ground suspender and suspender located at 1/4 span. Furthermore, it is found that the greater the depth-width ratio of the corrosion pit, the sharper shape the corrosion pit, thus the shorter the corrosion fatigue life of the steel wire with double corrosion pits. When the shape of double corrosion pits is asymmetric, the corrosion fatigue life of suspender steel wire is mainly determined by the pits with larger depth-width ratio.
The effect of NaNO3 and TU on the crevice corrosion of 7075 Al-alloy were investigated by mass loss measurements, electrochemical tests and scanning electron microscopy (SEM) in acidic sodium chloride solution. NaNO3 and TU show a certain inhibited effect on the corrosion of Al-alloy, respectively. Moreover, NaNO3 and TU could inhibit synergistically the corrosion of aluminum alloy. For the specimen with crevice, NaNO3 could inhibit the corrosion of specimen outside crevice. However, it could promote the corrosion of specimen inside crevice. It could be attributed to that the produced NH3 inside crevice due to the reduction of nitrate could selectively dissolve the intermetallic particles and induce the nucleation of pitting corrosion inside crevice. In the solution containing TU, the specimen inside crevice is hardly corroded, however, the specimen outside crevice is still seriously corroded. In the solution with NaNO3 and TU, the TU could adsorb on metal surface and inhibit the pitting corrosion inside crevice, while the NaNO3 could promote the formation passive film and inhibit the corrosion of specimen outside crevice.
The corrosion behavior of crevice configurations composed of 316L stainless steel combined with the same steel, poly tetra fluoroethylene (PTFE) and nitrile butadiene rubber (NBR) respectively in seawater environment was investigated comprehensively by deep-sea exposure, simulation deep-sea testing and electrochemical technique. The results show that after 30 d of exposure in the deep-sea environment, in the crevice area of the couple of 316 stainless steels shows uniform corrosion thinning, but the depth of the corrosion pit is relatively shallow. However, the crevices composed of 316L stainless steel contacting with inert materials such as PTFE and NBR exhibit local corrosion mainly at the boundary of the crevice, showing a preferential trend of corrosion extending to the depth. The results of electrochemical tests show that the crevice corrosion sensitivity of different configurations is 316L-316L>316L-PTFE>316L-NBR. The deep-sea simulation test can reproduce the same corrosion phenomena as the deep-sea exposure test, but for the same test period, the crevice corrosion of samples in the real-sea environment is much more serious than that in the indoor simulation environment.
The corrosion resistance and aging mechanism of polyurethane topcoat on Al-alloy plates used for high-speed train were studied by electrochemical impedance spectroscopy (EIS), ultraviolet aging, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that the polyurethane topcoat presented post-curing phenomenon after immersing in 3.5wt.%NaCl solution for 240 h. The topcoat/Al-alloy interface was slightly corroded within the period of 384-1560 h, and the corrosion product film was formed on the surface of Al-alloy substrate within 1920-2160 h. During the ultraviolet (UV) aging test, holes gradually emerged on the surface of polyurethane topcoat, which then became loose and spalling, meanwhile its glossiness gradually decreased with increasing reduction of glossiness, as well as its color difference increased and then tended to be stable. It follows that the visible light degradation was the main degradation in the early stage of aging, and UV degradation was the main degradation in the late stage of aging.
The influence of main components of ammonia desulfurization slurry on the development stage of localized corrosion for 304 stainless steel was studied by means of constant voltage occlusion battery and long-term static pitting corrosion test aiming to simulate the real local corrosion, as well as XPS and UV-VIS spectroscopy to characterize corrosion products and solutions. The results showed that low concentration (NH4)2SO4 in ammonia desulfurization slurry can promote the effect on localized corrosion development of 304 stainless steel, while high concentration can inhibit it. With the increase of Cl- concentration, the localized corrosion was intensified. The complex compounds on the surface resulted from the interaction of F- and metal ions, while the competitive migration effect with Cl- made the presence of F- have a certain inhibitory effect on the localized corrosion of stainless steel.
By taking the three working loads into account, namely pressure, temperature and pressure/temperature coupling, several finite element models for pipe parts with different inner diameters were constructed respectively, and then the triaxial distribution of pipe stresses of the special acid-, temperature- and pressure-resistant brick and Asplit HB cement was analyzed by different inner diameters of pipe nozzle under three working conditions. The dangerous degree of different positions of the pipe nozzle during working process is clarified. The results show that for the special acid-, temperature- and pressure-resistant brick, the larger the radius of the pipe opening, the larger the maximum tensile stress in the radial and annular direction under the action of pressure load. Under the action of temperature load, the maximum tensile stress in radial and axial direction increases. Under the coupled pressure/temperature load, the maximum tensile stress in all three directions increases. For Asplit HB cement, the maximum axial tensile stress increases with the increase of the radius of the pipe mouth under pressure load. Under the action of temperature load, the maximum tensile stress in the annular direction increases with the increase of the tube orifice radius, while in the axial direction, the maximum tensile stress decreases with the increase of the tube orifice radius. Under the pressure/temperature coupling load, the maximum radial tensile stress increases with the increase of the orifice radius.
The coating failure of blades caused by low melting point silicate composed of CaO,MgO,Al2O3,SiO2 has been widely concerned for an aero-engine in service. Therefore, the spreading and corrosivity of CMAS melt on five ceramic materials, i.e. Y2O3,La2Ce2O7,Gd2Zr2O7,Al2O3 and 12YSHf, as candidate materials for thermal barrier coatings, was assessed in air at 1250 oC for 16 h, in comparison with 7YSZ, the commonly used ceramic material. It can be found that 12YSHf and Al2O3 show good effect in slowing down the spreading of CMAS melt. In addition, the high temperature reaction interfaces of CMAS/Al2O3 and CMAS/La2Ce2O7 are all thinner than the others, which means that Al2O3 and La2Ce2O7 have better resistance to CMAS. Overall, the effect of Al2O3 in retarding the spreading and corrosion of CMAS is the most outstanding.
The Zn-6%Al-3%Mg coated steel plates were subjected to post-heat treatments at 500 ℃-10 min and 700 ℃-10 min, respectively. Then the microstructure, phase composition and corrosion resistance of the Zn-6%Al-3%Mg coated steel plates before and after heat treatment were comparatively characterized by SEM, XRD and neutral salt spray test. The results show that the morphology, phase composition and corrosion products of Zn-6%Al-3%Mg coated steel plate after heat treatment at 500 ℃-10 min are similar to those without heat treated ones, their corrosion mass changes are basically the same. However after heat treatment at 700 ℃-10 min, the coating structure changes from single-layer of multiphase structure to multi-layer of multiphase structure, it is worth noting that there are more Fe oxides in the corrosion products, which are mainly formed by the iron-rich phase precipitated on the surface of the coating. After corrosion test, the zinc-rich surface coating on the steel substrate kept completely intact, while the corresponding corrosion mass gain is 3.2 times of the un-heat treated ones, on the other hand, the corrosion mass loss is 2.2 times of the un-heat treated ones.
The hot corrosion behavior of Co-based alloys Co-9Al-9.5W-xNi (x=5, 15, 20, atomic fraction, %) beneath a film of molten salts mixture of 75% Na2SO4+25% NaCl in air at 900 °C were investigated by means of mass change measurement, SEM with EDS and XRD. The focus of the research is on the influence of Ni on hot corrosion resistance of the alloy Co-9Al-9.5W and the morphology and composition of the formed corrosion products. The results showed that the hot corrosion of the alloys may be characterized by both sulfidation and oxidation; with the increase of Ni content, the hot corrosion resistance of the alloy could be notably improved. The corrosion products scales on the three Co-based alloys were most composed of NiO, CoO, Al2S3 and CoNiO2. Finally, the hot corrosion mechanism of the Co-based alloy in the presence of 75% Na2SO4 and 25% NaCl deposits is also discussed.