Purpose The poor corrosion resistance of the ferrite-pearlite steel limits its application in marine engineering because of the enhanced galvanic effect caused by continuously accumulated cementite. Cr as one principal alloying element is commonly used to improve the corrosion resistance of steels. This paper aims to study the effect of Cr on corrosion behaviors of ferrite-pearlite steels in an acidic environment. Design/methodology/approach The tested steels were immersed in a simulated solution of 10 Wt.% NaCl with pH 0.85 for 72 h to evaluate the corrosion rate. After the immersion test, the corrosion morphologies and products were tested by scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. Meanwhile, an electrochemical workstation was used to study the electrochemical behaviors of samples. Findings At the initial corrosion stage, the corrosion rate increased in the sequence of Cr0, Cr0.5 and Cr1 steels, which was because of the competitive effect between the area ratio and the driving force caused by alloyed Cr. However, Cr1 steel exhibited the best corrosion resistance after a 72-h immersion test. This was because the alloyed Cr promoted the formation of protective Fe2O3 and FeCr2O4, which suppressed the preferential dissolution of ferrite and, thus, reduced the accumulation rate of carbides, resulting in the weakened galvanic corrosion. Originality/value This paper reports the role that Cr plays in the galvanic corrosion of ferrite-pearlite steels, which is important for the engineering application of ferrite-pearlite steels in marine environment.

Purpose The purpose of this paper is to study the cavitation erosion stages of AA5083 by electrochemical noise (EN). Design/methodology/approach EN technology including noise resistance and fast Fourier transform were used to characterize the electrochemical process during the cavitation erosion process. Findings AA5083 suffers from uniform corrosion during the cavitation erosion process. The whole cavitation erosion process can be divided into three stages: incubation stage, acceleration stage and steady-state stage. EN signals showed obvious differences in different stages of cavitation erosion. Originality/value EN technique is a suitable method that can be used to study cavitation erosion mechanism and identify cavitation erosion stages.

Purpose The purpose of this paper is to study the interaction of main marine organisms on localized corrosion of 316L stainless steel in the Dalian Sea area. Design/methodology/approach The steel plate was immersed in the Dalian Sea area for nine months to observe the biofouling and localized corrosion. The local potential distribution on the steel plate covered by marine organisms was measured. The local electrochemical measurements were performed to facilitate understanding the interfacial status under different biofouling conditions. The local surface morphologies and corrosion products were characterized. Findings The localized corrosion of stainless steel is mainly induced by the attachment of barnacles on the steel. The mussels have no influence on the localized corrosion. The cover of sea squirts could mitigate the localized corrosion induced by barnacles. Both crevice corrosion and pitting corrosion were found beneath the barnacle without the covering of sea squirts. The pitting damage was more serious than the crevice corrosion in the Dalian Sea area. The probing of sulfur element indicates that the potential growth of sulfate-reducing bacteria at barnacle center. Originality/value The above findings revealed that the interaction of marine organisms has significant influences on the localized corrosion of stainless steel. The influences of macro-fouling and micro-fouling on localized corrosion are discussed.

Purpose The purpose of this study is to modify cerium dioxide with fumaric acid (CeO2-f) to improve its compatibility and dispersibility in epoxy resin and to investigate the effect of the content on the coating performance. Design/methodology/approach To investigate whether CeO2-f reacts with epoxy resin by ring opening, CeO2-f and epoxy resin-treated CeO2-f (Ce CeO2-f/EP) were analyzed by infrared radiation (IR), X-ray diffraction (XRD) and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis). To reveal the effect of different content on coatings properties, neutral salt spray test (NSST) and electrochemical test were performed. Findings The results of IR, XRD, X-ray photoelectron spectroscopy and UV-Vis indicated that fumaric acid attached to the CeO2 surface by chemical bonding and underwent a ring-opening reaction with epoxy resin, thus, improving the compatibility of CeO2 in epoxy resin. NSST and electrochemical impedance spectroscopy results showed that the coatings containing 5% CeO2-f exhibited the optimal corrosion resistance. The reason is that a dense conversion film was established on the substrate surface. Originality/value The epoxy coatings using CeO2-f as fillers with synergistic inhibition ability are promising for the protection of carbon steel.

Purpose The purpose of this paper is to study the corrosion behavior of 316L stainless steel under cavitation condition in simulated seawater. Design/methodology/approach Electrochemical impedance spectroscopy and electrochemical noise analyses are used to characterize the electrochemical process during the cavitation erosion process. Findings Because of good corrosion resistance of this material, mechanical damage is the main cause of cavitation erosion. The alloy surface is in active dissolution state during the cavitation erosion process, and the corrosion rate is accelerated as time prolongs which is verified by electrochemical results. Originality/value Electrochemical noise is an effective way to study the corrosion under cavitation erosion process.

Purpose The purpose of this paper is to investigate the interfacial conductivity and corrosion resistance of the Ni–P/Ti4O7 composite coating that is deposited on a carbon steel substrate as bipolar plates for proton exchange membrane fuel cells. Design/methodology/approach The Ni–P/Ti4O7 coating was prepared by electroless plating. Scanning electron microscopy, white light interference, energy dispersive spectrometry and X-ray diffraction were used, respectively, to study the surface morphology, chemical composition and phase composition of coated samples. Electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization were used to test the electrochemical performance and corrosion behavior. The interfacial contact resistance (ICR) was measured via the standard method. Findings The surface of the Ni–P/Ti4O7 coating is complete and dense and without obvious defects. The electrochemical test results show that the Ni–P/Ti4O7 coating provides better corrosion resistance than the Ni–P coating and substrate. Compared with the Ni–P coating, the ICR of the Ni–P/Ti4O7 coating is lower by about 82.7%. This is because the coating has more conductive contact points. The more exciting thing is that the ICR of the Ni–P/Ti4O7 coating only increases to 12.38 mΩ·cm2 after 5 h of polarization. Originality/value This paper provides a method for achieving surface modification of metal bipolar plates. Introducing Ti4O7 particles in the Ni–P layer reduces the contact resistance before and after polarization while ensuring good corrosion resistance.

Purpose This paper aims to review the effect of traditional shot peening (SP), laser shock peening (LSP) and water jet cavitation peening (WJP) on microstructure evolution and corrosion behavior of austenitic stainless steels 316L and 304. Design/methodology/approach The effect of SP, LSP and WJP on corrosion behavior of 316L and 304 were discussed in terms of surface peening–induced change in surface roughness, stress state and grain size. Findings Residual compressive stress and grain refinement were introduced after SP, LSP and WJP treatment in 316L and 304 stainless steels. Superior corrosion resistance can be obtained by WJP compared with SP and LSP. Originality/value The relationship between SP-, LSP- and WJP-induced change in microstructure and stress state and corrosion resistance was summarized.

Purpose This paper aims to investigate the effects of Cr and Ta additions on the friction performance and corrosion-wear mechanism of Fe90-Al2O3 coating in 3.5% NaCl solution. Design/methodology/approach Cr and Ta reinforced Fe90-Al2O3 coatings were prepared on Q235 steel by laser cladding. The effects of Cr and Ta addition on the coefficient of friction (COF) and wear rate of Fe90-Al2O3 coating were investigated using a friction tester, and the wear model was established to discuss its corrosion-wear mechanism. Findings The average COFs of Fe90-Al2O3, Fe90-Al2O3-10%Cr and Fe90-Al2O3-10%Ta coatings in 3.5% NaCl solution are 0.57, 0.42 and 0.75, respectively, and the corresponding wear rates are 9.42 × 10−7, 5.31 × 10−7 and 7.02 × 10−7 mm3 s−1 N−1, respectively. The corrosion-wear resistance of Fe90-Al2O3-10%Cr coating is the best among the three kinds of coatings, in which the additions of Cr and Ta play a role in solid solution strengthening. Originality/value The Fe90-Al2O3 coating was strengthened by the additions of Cr and Ta to improve its corrosion-wear resistance in 3.5% NaCl solution.

Purpose The corrosion problem of the tank bottom plate is growing more and more obvious as the usage period of the tank increases. The purpose of this study is to explore the specific effects of various factors on the potential distribution of the tank bottom plate and propose reasonable cathodic protection measures for tanks through simulation and indoor tests. Design/methodology/approach In this paper, several aspects (such as anode conditions, soil resistivity and so on) impacting the potential distribution of the tank bottom plate are explored by means of indoor tests and MATLAB software simulations, and the related results are presented using Origin software plots. Findings The results show that the potential value of the tank bottom plate is positively shifted with the increase of anode well depth and distance and the decrease of output current, and the overall potential distribution uniformity is higher; the anodic well output current has the greatest influence on potential distribution; to set up regional cathodic protection in the multitank area, the anodic well should be arranged in the central position between multiple tanks. Regional cathodic protection potential distribution for multiple anodes is more uniform, but a reasonable number of anodes should be selected, usually 2–3 anodes. Originality/value This paper provides solid theoretical and technical support for the future establishment of cathodic protection systems in station yards, as well as the renewal and transformation of cathodic protection systems in old tanks, by investigating the influencing factors on the potential distribution of tank bottom plate and verifying them through indoor experiments.

Purpose This paper aims to focus the synchronous chemical conversion technology–based titanium/zirconium composite on 6061, 7075 aluminum alloys and galvanized steel. Design/methodology/approach The effects of pH, temperature, reaction time and other process parameters on the corrosion resistance of the three metal surface coatings were investigated by copper sulfate drop and electrochemical corrosion performance tests under a certain content of H2TiF6 and H2ZrF6. The surface morphology and element distribution of the conversion coating were analyzed by scanning electron microscope and X-ray photoelectron spectroscopy. Findings The results show that the optimal synchronization chemical conversion conditions of 6061/7075 aluminum alloys/galvanized steel are controlled as follows: H2TiF6 2.2 mL/L, H2ZrF6 1 mL/L, pH 3.9, conversion temperature 35°C and conversion time 120 s. Originality/value Multi-metals chemical conversion coating can be obtained simultaneously with uniform corrosion resistance and surface morphology. The presence of microdomain features in multiple metals facilitates simultaneous chemical conversion into coatings.

Purpose The purpose of the present study is to investigate the effects of strain-induced martensite (SIM) and its reversal on metastable austenitic stainless steel (MASSs) through the analysis of metallurgical and sensitisation behaviour. Design/methodology/approach In the present investigation, the samples of Cr-Mn ASS (also known as MASSs) including 15%, 30% and 50% cold worked, solution annealed samples with and without thermal ageing (at 700°C for 3 h) were analysed with the help of X-ray diffraction analysis, microstructure examination and electrochemical behaviour. The scanning electron microscope (SEMJOEL 6380 A) was used to examine the microstructure of the sample, and the double-loop electrochemical potentiokinetic reactivation test was used to determine the degree of sensitisation (DOS) in the samples. The cold worked solution annealed samples without thermal ageing are named as CR15, CR30 and CR50, respectively, and the samples with thermal ageing are named as CR15_TA, CR30_TA and CR50_TA, respectively. Findings In CR15, CR30 and CR50 samples, the DOS increased with increase in the extent of cold working, which was attributable to passivation deterioration. Because of the high degree of passivation at the grain boundaries, the DOS of CR15_TA and CR30_TA were practically identical. The DOS in the CR50_TA sample, on the other hand, was lowered due to SIM recovery in the austenite. Originality/value The present study sheds light on how to choose the right cold working percentage to avoid sensitisation in MASSs during the fabrication of metal forming components.

Purpose In line with current research efforts to develop eco-friendly strategies for corrosion mitigation, the purpose of this study is to appraise the anti-corrosion potential of selected amino acids on magnesium corrosion in sodium chloride solutions. Design/methodology/approach The corrosion inhibition of magnesium in aqueous solutions in the presence of benign, eco-friendly and readily available amino acids (alanine, arginine, histidine, lysine, proline) were evaluated using electrochemical methods. Findings Amino acids suppressed magnesium corrosion rate in aqueous sodium chloride solutions. The order of inhibition efficiency (%IE) was as follows: alanine < arginine < histidine < lysine < proline. The open circuit potential shift with respect to the blank was less than 0.085 VSCE, indicating that the amino acids are mixed-type corrosion inhibitors. In addition, the %IE of the amino acids was inversely proportional to the molecular weight. The results obtained indicate that the amino acids can serve as sustainable eco-friendly corrosion inhibitors for magnesium with the best inhibition efficiency attributed to proline with an efficiency of 85.1%. Originality/value New information on the application of amino acids as green sustainable corrosion inhibitors is provided herein.

Purpose This study aims to develop a sol-gel-based coating to provide a long-lasting corrosion protection on AZ31 Mg alloy. Silane-based sol-gel coatings have been successfully applied to Mg alloys for corrosion protection. However, the micro or nano defects formed during condensation and solidification will cause the coating failure during a long-lasting immersion in a saline solution. More durable corrosion-protective sol-gel coatings are needed. Design/methodology/approach A sol-gel-based coating was modified on AZ31 Mg alloy by levodopa (DOPA). The long-lasting corrosion protection mechanism was studied by multiple electrochemical testing methods and surface characterization techniques. Findings Long-term testing by electrochemical impedance spectroscopy in aqueous 0.1 M NaCl indicated that the modified DOPA@sol-gel coating exhibited significant corrosion protection performance (>14 days). In comparison, the DOPA-free sol-gel coating failed only after three days of testing. The improved corrosion protection is attributed to the self-polymerized DOPA filling to the micro or nano defects in the glassy cross-linked networks of the sol-gel coating, which greatly improves the compactness of the coating. Originality/value The method of this study is simple and easy to process, the raw materials are green and the protective effect is excellent, which is of significance for the study of magnesium alloy corrosion protection.

Purpose This paper aims to verify weather atmospheric plasma spray (APS) in situ remelting posttreatment is effective for densifying the porous FeCoCrMoCBY amorphous alloy (FAA) coating and improving the antiabrasion and anticorrosion performances or not. Design/methodology/approach APS was used to deposit and in situ densify FAA coating on the 40Cr substrate. Scanning electron microscope, X-ray diffractometer, energy dispersive spectroscopy, neutral salt spray, hardness and wear behavior test were used to evaluate the densifying effects. Findings APS remelting technology can effectively improve the hardness of the coating by reducing the porosity. After remelting at 30 kW power, the hardness of the coating increased by about 260 HV0.2 and the porosity decreased to 2.78%. The amorphous content of the coating is 93.9%, which is about 3.5% lower than original powders. The electrochemical impedance spectrum and neutral salt spray test results show that APS remelting can reduce the corrosion rate by about 62.7%. Originality/value APS remelting method is firstly proposed in this work to replace laser remelting or laser cladding methods. APS remelting method can effectively improve the corrosion and abrasion resistance of the FAA coating by increasing the densification with much low recrystallization, which is big progress for application of FAA coatings.

Purpose This study aims to control the oxidation resistance of Co-based deformed superalloys by adding trace elements Hf and Si. Design/methodology/approach The effects and mechanism of trace elements Hf and Si on the oxidation behavior of Co-Ni-Al-W-based forged superalloys were investigated by cyclic oxidation at 900°C. Findings The results show that the addition of trace elements Hf and Si does not affect the type of surface oxides of Co-Ni-based superalloys, and the oxidation layers of the alloys are TiO2, spinel, Cr2O3, TaTiO4, Al2O3 and TiN from outside to inside. However, the addition of elements can affect the activity of Cr and Ti elements; decrease the formation of TiO2 and TaTiO4 layers, which are harmful to the oxidation performance; and then improve the oxidation resistance of the alloy. Originality/value The relevant research results can not only optimize the microalloying element content of Co-Ni-Al-W-based superalloys, but also provide a new perspective for the composition optimization design of superalloys.

Purpose This study aims to report the oxidation behaviors of the T91 ferritic/martensitic steel (T91 steel) and 304 austenitic stainless steel (304 steel) in supercritical water (SCW) at 600°C. Design/methodology/approach The microstructure, elemental distribution and phase structure of the oxidation layers derived from the corrosion of the T91 steel and 304 steel were analyzed by scanning electron microscopy, Oxford Instrument X-ray spectroscopy, electron scattered diffraction and transmission electron microscopy. Findings The oxidation layers on the T91 steel and 304 steel have duplex structure. The two steels all suffer internal oxidation, and the phase of the internal oxidation layers are indexed as Fe-Cr spinel, although their morphologies are different. The formation of a continuous Cr-rich layer is not detected because of the relatively low Cr content of the steels, which is attributed to the corrosion property. Originality/value The accelerated corrosion and corrosion mechanism of the T91 steel and 304 steel with low Cr occurring in SCW at 600°C was clarified.

Purpose The purpose of this paper is to identify corrosion types and corrosion transitions by a novel electrochemical noise analysis method based on Adaboost. Design/methodology/approach The corrosion behavior of Q235 steel was investigated in typical passivation, uniform corrosion and pitting solution by electrochemical noise. Nine feature parameters were extracted from the electrochemical noise data based on statistical analysis and shot noise theory. The feature parameters were analysis by Adaboost to train model and identify corrosion types. The trained Adaboost model was used to identify corrosion type transitions. Findings Adaboost algorithm can accurately identify the corrosion type, and the accuracy rate is 99.25%. The identification results of Adaboost for the corrosion type are consistent with corroded morphology analysis. Compared with other machine learning, Adaboost can identify corrosion types more accurately. For corrosion type transition, Adaboost can effectively identify the transition from passivation to uniform corrosion and from passivation to pitting corrosion consistent with corroded morphology analysis. Originality/value Adaboost is a suitable method for prediction of corrosion type and transitions. Adaboost can establish the classification model of metal corrosion, which can more conveniently and accurately explore the corrosion types. Adaboost provides important reference for corrosion prediction and protection.

Purpose This paper aims to reveal the corrosion mechanism and corrosion development regulation of marine engineering structural steel in the marine environment and provide constructive suggestions for marine immersed tunnel engineering. Design/methodology/approach In this study, marine engineering structural steel’s behavior and corrosion prediction were carried out under the conditions of no cathodic protection and under-protection by artificially adding dissolved oxygen in a simulated seawater solution as a depolarizing agent. Findings Marine resources are rich in China. With the development of the economy and the improvement of engineering technology, marine engineering structural steel is used more and more widely. Engineering structural steel has a great risk of corrosion failure for long-term service in seawater, as seawater is a kind of corrosive medium containing various salts. At present, there are few projects and research studies available on the corrosion in the seawater environment of Q390C engineering structural steel, which is used in the Shenzhen–Zhongshan Link immersed tunnel steel shell at home and abroad. It cannot guide the corrosion of immersed tunnel steel shells in the ocean. Originality/value In this paper, the corrosion mechanism and corrosion development regulation of marine engineering structural steel in the marine environment are studied by accelerated corrosion test in the laboratory, which is of great significance to ensure the long-life durability of the immersed tunnel in marine engineering.

Purpose This study aims to enhance to corrosion protection of NiZn-plated steel by electroplating multilayer coating. Design/methodology/approach The multilayer coating consists of three layers on mild steel substrate, such as Cr3+ chromate conversion layer (CCC), electrodeposited nanosilica zinc-nickel composite layer (ZnNiSi) and electrodeposited zinc-nickel alloy layer (ZnNi). Its morphology, composition and corrosion behaviour were investigated by various methods. Findings Polarization curves indicated that polarization resistance and corrosion current density of CCC/ZnNiSi/ZnNi/Fe (6.956 kO.cm2; 2.56 µA.cm−2) were two times higher and five times lower than that of ZnNiSi/ZnNi/Fe (3.42 kO.cm2; 12.52 µA.cm−2), respectively. From electrochemical impedance spectroscopy data, charge transfer resistances were 1.344, 2.550 and 2.312 kO.cm2 for ZnNi, ZnNiSi/ZnNi and CCC/ZnNiSi/ZnNi, respectively. Salt spray test indicated that after 48 h, surface of ZnNi and ZnNiSi was covered by white rust, whereas no white rust was observed on surface of CCC/ZnNiSi/ZnNi. After 600 h, there were red rust spots (1% surface coverage) on surface of Zn-Ni, whereas only white rust was observed on both ZnNiSi/ZnNi (100% surface coverage) and CCC/ZnNiSi/ZnNi (10% surface coverage). Originality/value Multilayer coating enhanced significantly the corrosion protection for steel, as compared to the single-layer coating.

Purpose The purpose of this paper is to review the application of digital holography in studies of the corrosion of metallic materials. Design/methodology/approach Digital holography is used for in situ observation of the dynamic processes at the electrode | electrolyte interface and on the electrode surface during the corrosion dissolution of metallic materials. Findings Digital holography is an effect method to in situ observe the corrosion processes, and it can provide a direct experimental foundation for studying the corrosion mechanism. Originality/value Even though there are several challenges, digital holography will play a significant role in studying corrosion processes.