Corrosion Resistance In Seawater Research Articles

Tailoring the corrosion behavior and mechanism of AZ31 magnesium alloys by different Ca contents for marine application

The microstructure of AZ31 magnesium alloy was modified by Ca addition. AZ31-Ca alloys with refined microstructure exhibited significantly enhanced corrosion resistance in artificial seawater. AZ31–0.5Ca showed the lowest corrosion rate of 0.716 ± 0.186 mm y−1, which was about 7.4 times lower than that of AZ31 alloy (5.326 ± 0.652 mm y−1). The dominant role in the reduced corrosion rates of AZ31-Ca alloys gradually changed from the compact corrosion products film containing Al2O3 and CaCO3 to the corrosion barriers consisting of net-like (Mg, Al)2Ca phases as the Ca content increased from 0.1 wt% to 1.5 wt%.

Structure and tribological behavior of CrAlCN coating in artificial seawater

This study examined the tribological behavior of CrAlCN coatings on 316 l stainless steel and TC4 alloy sliding against Si3N4 ball in seawater. The coatings were systematically investigated by XRD, XPS, SEM, TEM and EDS. The mechanical and tribological properties were analyzed by nano indentation test and tribometer, respectively. The results showed that the coating contained CrN, CrC, AlN and amorphous (α–C) phases. The nanocrystalline was surrounded by α–C phases. The hardness of CrAlCN coatings on both substrates was about 21 GPa. The CrAlCN coating on TC4 had the highest Open Circuit Potential, lowest corrosive current density and wear rate, indicating that it had the best wear resistance and corrosion resistance in seawater.

Influence of Annealing Treatments on Welded CuNi Sheets on the Corrosion Behaviour in Sea Water

Due to their good corrosion resistance in seawater, tubes, rods, and forgings made from copper-nickel alloys (Cu-Ni) are widely used in ship building, offshore platforms, desalination plants, and numerous other applications. Welding is a major technology for joining this material. Since the microstructures of base material, weld seam, and heat affected zone may be quite different, the consequences with respect to corrosion must be considered. In this study the influence of microstructure on corrosion behaviour was investigated using welded test coupons of CuNi10Fe1.6 Mn, as-welded and after heat-treatment, by metallographic examination and electrochemical corrosion tests in synthetic seawater.

Characterization of ta-C film on micro arc oxidation coated titanium alloy in simulated seawater

The harsh marine environment puts forward higher performance requirements for titanium alloy parts, and it is urgent to develop advanced surface protection technology. In this paper, micro arc oxidation (MAO)/tetrahedral amorphous carbon (ta-C) composite coatings were fabricated via MAO processing and filtered cathodic vacuum arc (FCVA) system on TC4 titanium alloy. The surface morphologies, tribological properties and corrosion resistance in simulated seawater of the coatings were investigated. The results showed that, compared with the monolayer of MAO coating or ta-C film, the MAO/ta-C composite coating still showed porous characteristics and had an improved bonding force. Due to compact oxide ceramic coating of MAO coating and self-lubrication of ta-C film, the MAO/ta-C composite coating had the lowest friction coefficient (0.13) and width of wear scar (356.84 um) in all samples. The lowest corrosion current density (8.321 × 10−9 A/cm2) and highest corrosion potential (−0.012 V) in the simulated seawater solution confirmed the most effective corrosion protection provided by the MAO/ta-C coating. These research results could provide important support for promoting the application of titanium.

Tribological Behaviors of Si3N4-hBN against PEEK with Precorrosion in Seawater

In this article, the tribological behaviors of Si3N4-hBN composites and polyether ether ketone (PEEK) materials with precorrosion were investigated in seawater and deionized water, respectively. Si3N4-hBN composite represented a good seawater corrosion resistance, and a low corrosion rate of 0.0037 g/(m2·h) was obtained for Si3N4-hBN composites in seawater. The seawater absorption rate of PEEK material was about 0.726%, and the surface became rougher with precorrosion. Si3N4-hBN/PEEK pairs presented friction coefficients of around 0.20, and some reactive products (e.g., SiO2 and H3BO3) formed on the surface. When the hBN content was equal to 10 wt%, more smooth worn surfaces were presented. In addition, the Si3N4-10% hBN/PEEK pair presented the lowest and most stable friction behavior. There were few changes in the Si3N4-hBN and PEEK materials before and after immersion in deionized water. The friction coefficients of the Si3N4-hBN/PEEK pair were all lowered than 0.1 in deionized water. The corresponding wear rates of pins and discs were all below the order of magnitude of 10−6 mm3/Nm. The excellent tribological characteristics were attributed to ultrasmooth surfaces (originated from the tribochemical reaction).

Influence of Non-metallic Inclusions on Corrosive Properties of Polar Steel

Polar steel requires excellent toughness and corrosion resistance for breaking icy surfaces in low-temperature seawater environments. In this study, the effect of inclusions on the corrosion resistance of polar steel was examined. In the experiments conducted, the composition and morphology of the inclusions in steel were controlled using different deoxidation methods during steel refining. The morphology and composition of the corrosion-resistant active inclusions were analyzed using scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of polar steel was determined by measuring the saturation current density of the anodic dissolution of steel in a corrosive medium via an electrochemical method. The corrosion resistance under simulated seawater was also investigated under laboratory conditions. It was found that as the ratio of Al/Mg approaches the stoichiometric composition of the spinel (2.3–2.5), the inclusions become less active; as the ratio increases further, the corrosion-resistant activity increases due to the formation of MgAl2O4⋅CaO complexes, leading to an increase in local stress around the inclusions. If steel is deoxidized with Zr–Ti, small Zr–Ti complex oxides form in the steel, providing nucleation particles for the precipitation of spheroidized and uniformly distributed MnS. Therefore, steel deoxidized with Zr–Ti has better seawater corrosion resistance than Al-deoxidized steel.

Influence of Processing Technology on Electrochemical Corrosion Behavior of Ti-6Al-4V Alloys

Ti-6Al-4V alloys are typically used for biomedical implants, aerospace components, and offshore equipment, where corrosion resistance is critical. In the present paper, the electrochemical corrosion behaviors of Ti-6Al-4V alloys made by different traditional processing and 3D printing technologies in seawater, 3.5 wt% NaCl, 3.5 wt% HCl, 5 wt% HCl, and 10 wt% HCl solutions were studied through polarization curve and electrochemical impedance spectra analyses. The influences of microstructure and printing parameters on the corrosion behaviors of Ti-6Al-4V alloys were analyzed. In addition, the corrosion current density, film resistance, and charge transfer resistance of traditionally processed Ti-6Al-4V and 3D-printed Ti-6Al-4V in the five solutions were compared. The results show that Ti-6Al-4V possesses a better corrosion resistance in seawater than in 3.5 wt% NaCl, and that the corrosion rate increases with the HCl concentration. Besides, 3D printed Ti-6Al-4V shows a higher corrosion rate in comparison with traditionally processed Ti-6Al-4V because pores are effortless to enrich Cl−. Finally, the ratio of laser power to its scanning speed and the phase constituent composition of the alloy have slight influences on its electrochemical corrosion behavior. It is suggested that, for the 3D-printed alloy, the deterioration of mechanical properties induced by corrosion damage during servicing should be assessed and considered.

Microstructure and Corrosion Properties of La2Zr2O7/NiCoAlY Thermal Barrier Coatings Deposited on Inconel 718 Superalloy by Laser Cladding

In order to improve the seawater corrosion resistance of Inconel 718 superalloy, a La2Zr2O7/NiCoCrAlY thermal barrier coating corrosion resistant to 3.5 wt.% NaCl aqueous solution was prepared by laser cladding on Inconel 718 superalloy. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and electrochemical techniques were used to study the microstructure and the corrosion performance of the coating in 3.5 wt.% NaCl solution. The results show that the thermal barrier coating is mainly composed of primary La2Zr2O7 phase and γ + laves/δ phase eutectic structure. The corrosion potential and corrosion current of the coating in 3.5 wt.% NaCl solution are higher and lower than that of the Inconel 718 substrate, respectively, indicating that the corrosion performance of the coating is better than that of the Inconel 718 substrate. The presence of La2Zr2O7 phase in the thermal barrier coating is the main reason for its corrosion resistance to 3.5 wt.% NaCl solution.

Fabrication of Ni–Co–P Alloy Coatings Using Jet Electrodeposition with Varying Reciprocating Sweep Speeds and Jet Gaps to Improve Wear and Seawater Corrosion Resistance

Type 45 steel substrate surfaces were coated with Ni–Co–P alloy coatings using jet electrodeposition in varying reciprocating sweep speed and jet gap to improve the wear and seawater polarization resistance of the substrate surface. The properties of the deposited coatings were analyzed and characterized. The results showed that the morphologies of the cross-section, thickness, and chemical composition of coatings were affected by reciprocating sweep speed and jet gap variation. At a reciprocating sweep speed of 175 mm·s−1 coupled with a jet gap of 2.0 mm, the content of Co element in the deposit attained the highest value of 47.66 wt.%. Reciprocating sweep speed and jet gap variation exhibited no significant influence on either the phase structure or the peak intensities of deposited Ni–Co–P coatings, but an obvious preferred orientation was evident in the (111) plane. Further increase in reciprocating sweep speed and jet gap caused an initial increase in the microhardness of Ni–Co–P alloy coatings followed by a decrease, where the highest value attained was 635 HV0.1. At a jet gap of 2.0 mm and a reciprocating sweep speed of 175 mm·s−1, Ni–Co–P alloy coatings reached a minimum wear scar width value of 460 µm. Electrochemical tests showed that the seawater corrosion resistance of coatings exhibited an observable change with increased reciprocating sweep speed and jet gap. The Ni–Co–P alloy coatings exhibited the highest polarization resistance (Rp) of 28.32 kΩ·cm−2 when the reciprocating sweep speed was 175 mm·s−1 and the jet gap was 2.0 mm, which indicated that the coatings had better seawater corrosion resistance.

Freeze-thaw resistance and seawater corrosion resistance of optimized tannery sludge/metakaolin-based geopolymer

In this study, tannery sludge was used to synthesize a geopolymer with optimum mixing proportions of raw material determined using Design-Expert. Compressive strength and total chromium leaching concentration were considered as markers for evaluating the performance of the geopolymer as a building material. The durability of the geopolymer in terms of freeze-thaw resistance under sulfate attack and seawater corrosion resistance was also studied. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests were performed for the micro-analysis. The results demonstrate that the geopolymer exhibited optimal performance when metakaolin, tannery sludge, sodium silicate, and sodium hydroxide used for the synthesis were mixed in the ratios 50.34%, 13.48%, 28.95%, and 7.23% (weight%), respectively (deionized water was added in a liquid-solid ratio (L/S) of 1:10 (mL/g)). For these mix proportions, the compressive strength of the geopolymer reached 50.37 MPa, while the total chromium leaching concentration was 2.440 mg/L (the chromium retention rate was 97.93%) at 7 days. Meanwhile, the geopolymer exhibited good resistance to seawater corrosion and certain anti-sulfate attack-freeze-thaw coupling ability. After 21 days of seawater corrosion test and 14 cycles of sulfate attack-freeze-thaw test, the compressive strength of the geopolymer was 32.64 MPa and 19.48 MPa, respectively. Thus, the geopolymer has potential as a building material in cold coastal environments.

Microstructure and tribological properties of AlCrFe2Ni2W0.2Mo0.75 high-entropy alloy coating prepared by laser cladding in seawater, NaCl solution and deionized water

Ocean engineering equipment frequently undergoes tribological impacts during service, resulting in an accelerated deterioration of ocean materials. Thus an effective strategy by introducing high entropy alloy coating was proposed to protect ocean engineering equipment. Accordingly, a new wear-resistant AlCrFe2Ni2W0.2Mo0.75 high entropy alloy coating was designed and deposited on Q235 steel by laser cladding. The corresponding microstructure, microhardness, corrosion resistance and tribological properties in artificial seawater, 3.5 wt% NaCl solution and deionized water were investigated deeply. The microstructure of coating presents a weave-like morphology and consists of BCC and ordered B2 phases. Its hardness is approximately 630.88 HV, which is almost 4.6 times than that of substrate. In addition, the coating exhibits better tribological properties than Q235 steel substrate and SUS304 in NaCl solution and seawater. And the friction and wear of coating in seawater are the mildest among all environments. It is mainly due to the lubrication effect of Mg(OH)2, CaCO3 and Ca(OH)2, as well as the formation of other metal hydroxides and oxides on worn surface of coating, which isolates and reduces wear and friction, resulting in a decrease in friction coefficient and wear rate. Besides, the coating has better corrosion resistance than Q235 substrate and SUS304 in seawater. These suggest that the AlCrFe2Ni2W0.2Mo0.75 coating is a promising material for surface protection of ocean engineering equipment.

Study on the Wear and Seawater Corrosion Resistance of Ni–Co–P Alloy Coatings with Jet Electrodeposition in Different Jet Voltages and Temperatures of Plating Solution

In order to improve the wear and seawater corrosion resistance of metals, Ni–Co–P alloy coatings were fabricated on 45 steel substrates with jet electrodeposition in different jet voltages and temperatures of plating solution. The cross-section morphology, chemical composition, crystalline structure, microhardness, wear, and seawater corrosion resistance of the samples were analyzed and characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness tester, friction wear tester, and electrochemical workstation, respectively. The results showed that the contents of Co in Ni–Co–P alloy coatings changed with the variation of jet voltages and temperature of plating solution. The content of Co in Ni–Co–P alloy coatings reached a maximum value of 47.46 wt·% when the jet voltage was 12 V and the temperature of the plating solution was 60 °C. The XRD patterns of Ni–Co–P alloy coatings showed that there was an obvious preferred orientation in the (111) plane. With an increase in the jet voltages and temperature of the plating solution, the microhardness of Ni–Co–P alloy coatings first increased and then decreased, with the maximum value obtained being 634.9 HV0.1. When the jet voltage was 12 V and the temperature of the plating solution was 60 °C, the wear scar width of the Ni–Co–P alloy coatings reached a minimum value of 463.4 µm. In addition, the polarization curves in the electrochemical test indicated that the samples deposited at 60 °C and 12 V exhibited the lowest corrosion current density (Icorr) of 1.72 µA/cm2 and highest polarization resistance (Rp) of 19.61 kΩ·cm−2, which indicated that the coatings had better seawater corrosion resistance.

Preparation of graphene/Fe3O4 composite varnish with excellent corrosion-resistant and electromagnetic shielding properties

In this work, a novel 3D graphene/Fe3O4 (G-Fe3O4) nanocomposite was prepared by a facile one-pot hydrothermal process used to be adulterated into the varnish as an anticorrosive and electromagnetic shielding paint. It is confirmed that the skeleton structure of graphene can effectively inhibit Fe3O4 agglomeration by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) technique, and the G-Fe3O4 nanocomposites can be well dispersed in the varnish for a longtime without settling. The graphene/Fe3O4 composite varnish shows excellent corrosion resistance both in city water and seawater, besides its corrosion resistance is also superior to that of ordinary anti-rust paint. Moreover, the electromagnetic shielding test confirms that the as-prepared composite varnish shows well electromagnetic shielding performance. This new type of composite varnish has a broad application prospect to be used as urban exterior wall and ships paint.

Study of seawater corrosion resistance of ordinary Portland cement–aluminate cement–gypsum mortar containing slag

A repair material for use in the marine environment is developed. The ternary cementitious system (TCS), which contains ordinary Portland cement, calcium aluminate cement and gypsum, causes rapid hardening and displays high strength, and hence can be used as a building repair material. However, the hydration products of the TCS contain a large amount of ettringite, calcium hydroxide and calcium aluminate hydrate, which can be easily corroded by the inorganic ions in seawater. Owing to its pozzolanic activity and ability to bind chloride, slag is added to the TCS. The content of slag in the TCS is a critical factor; hence, the effects of 0–35 wt% slag on the compressive strength, mass change, apparent porosity, and free and total chloride content of TCS immersed in seawater are investigated. The systems with slag show a higher compressive strength than the TCS in seawater, and the reduction in compressive strength of the system with 25 wt% slag is only 14·14% after 180 d. Also, the addition of slag significantly reduces the free and total chloride content of the TCS immersed in seawater. The optimum amount of slag in the TCS is determined to be about 25 wt%.

Reliability analysis of wood-plastic composites in simulated seawater conditions: Effect of iron oxide pigments

The objective of this work was to assess and verify the potential loss in composite structure, surface properties, structural strength, and thermal stability of pigmented wood-plastic composites under seawater corrosion conditions. For this purpose, three types of inorganic pigments were utilized and incorporated into a wheat straw fiber-reinforced polyvinyl chloride (PVC) composite. These pigments are: an iron oxide red, an iron oxide yellow, and an iron oxide blue (i.e., three fine-arts primary colors). An artificial seawater accelerated corrosion experiment was carried out. The results show that wheat straw fiber-reinforced PVC composites pigmented with iron oxide pigment have better seawater corrosion resistance, including better fiber/matrix interfacial interaction, lower total discoloration, and higher surface hydrophobicity, mechanical properties, and thermal stability. From these results, positive relationships between inorganic pigments and service reliability are confirmed for wood-plastic composites under seawater corrosion conditions.

Corrosion Resistance and Microstructure of Welded Duplex Stainless Steel Surface Layers on Gray Cast Iron

The degradation of pump components by corrosion and complex, simultaneous damage mechanisms, e.g., erosion–corrosion and cavitation–corrosion leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, surface welding of duplex stainless steel on gray cast iron parts was performed using inert shielding gas metal arc surface welding (GMA-SW) and plasma transferred arc surface welding (PTA-SW). The thermal conductivity of the used shielding gas and the preheating temperature influenced the dilution of the surface layers, which had a major impact on the corrosion resistance and the microstructure. Lower cooling rates enhanced diffusion and lead to precipitation of carbides. High heat input and prolonged cooling times during surface welding resulted in high dilution and a carbide network. The corrosion resistance in artificial seawater of those surface layers was substantially reduced compared to surface layers with lower heat input and higher cooling rates. The corrosion of the surface layers in the potentiodynamic polarization test was driven by selective corrosion of the phase boundary between Cr–carbides and Cr–depleted austenite. Passive behavior was observed for surface layers with low dilution, which had homogeneous chromium distribution and no carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surface welding with duplex stainless steel. The corrosion resistance of the surface layers produced with PTA-SW with no preheating exceeded that of the surface layers produced with GMA-SW and came close to those of a commercially available duplex stainless steel used as reference material.

Structural, tribological and corrosion properties of plasma nitrided-chromized-316L stainless steel in air and artificial seawater

To improve the protective performance of 316L stainless steel surface in seawater, a series of modified layers on the 316L stainless steel were fabricated by plasma nitriding, vacuum solid powder chromizing and duplex surface treatment of nitriding-chromizing, respectively. The microstructure, mechanical properties, tribological properties and corrosion resistance of different modified layers were contrastively investigated. The results of x-ray diffraction (XRD) and transmission electron microscope (TEM) showed that the nitrided layer was mainly CrN and Fe4N phases, and the chromized layer was mainly Fe-Cr and Cr23C6 phases. The surface hardness of 316L stainless steel was improved to varying degrees by nitriding and chromizing due to the formation of hard phases such as CrN and Cr23C6 on the surface of 316L. The friction coefficient and wear rate can be obviously reduced by nitriding treatment. However, the nitriding treatment can cause the precipitation of Cr from the solid solution of 316L to form CrN, resulting in the decrease of corrosion resistance in seawater. In contrast, chromizing treatment can significantly improve the corrosion resistance of 316L by increasing the chromium content of stainless steel surface. The duplex surface treatment of nitriding and chromizing made the 316L stainless steel had the highest surface hardness and plastic deformation resistance and showed the excellent tribological properties in both atmosphere and seawater.

Effect of Stress Ratio and Notch on Fatigue Strength of Commercial Pure Titanium

Titanium alloys such as Ti-6Al-4V are widely used in the aerospace domain worldwide; consequently, they have been extensively investigated, and the accumulated data has facilitated their use in the construction of structural members. In contrast, commercial pure (CP) Ti, which is cheaper than Ti alloys is widely used in the general industry, especially in the marine domain in Japan because it exhibits superior seawater corrosion resistance and biocompatibility. However, CP titanium has a strong anisotropy and consists of an hcp crystal structure; therefore, the strength data are insufficient owing to its short use history as a structural material, and some of its mechanical material properties remain unclear. Herein, the effect of mean stress and stress concentration on the fatigue strength of CP Grade 2 titanium was evaluated for the application range expansion of CP titanium. The results indicated that the fatigue limit in the longitudinal direction was 80–84% that in the transverse direction for smooth specimens. However, no significant difference was noted in the fatigue limit in both the directions for notched specimens. Furthermore, it was noted that it is necessary to apply at least Sa-0.5Su line to design the safe side in CP Grade 2 titanium.

Preparation of (3-mercaptopropyl)trimethoxylsilane film on brass and its corrosion resistance in natural seawater

Preparation of 3-mercaptopropyl)trimethoxylsilane (PropS-SH) film on brass surface and its corrosion resistance performance were investigated by surface energy analysis, Fourier transform infrared reflection (FT-IR) spectroscopy and electrochemical measurements. The results indicated that the generation of PropS-SH sialne film on brass was based on spontaneous reactions to produce Cu-S, Zn-S bond and Si-O-Si bonds. When the brass substrate was covered with the prepared PropS-SH silane film, the dezincification coefficient of brass decreased from 4.45 to 0.47. The PropS-SH silane film was able to minimize the dissolution of both Cu and Zn, improving the corrosion resistance of brass in natural seawater.

Cavitation erosion mechanisms in Co-based coatings exposed to seawater.

The cavitation erosion (CE) of most materials in seawater is more serious than in fresh water due to the onset of corrosion; however, in a previous study we reported results that contradict this widely accepted trend. In this research our objective is to provide fundamental insight into the mechanisms that may be responsible for these earlier results. To accomplish this objective, two types of Co-based coatings, prepared by high velocity oxygen fuel (HVOF) spraying system, were used to further investigate the underlying corrosion-mitigating CE mechanism in seawater. Accordingly, the influence of spraying parameters on microstructure, composition and mechanical properties of the coatings was analyzed on the basis of SEM, XRD, Raman spectroscopy, Vicker's hardness and nano-indentation results. Electrochemical corrosion tests were used to evaluate the corrosion behavior of the Co-based coatings. Their CE performances in seawater and deionized water were comparatively studied by a vibratory apparatus. Results demonstrated that a higher flame temperature facilitated the oxides formation with associated improvements in compactness, hardness and toughness of the coatings. The presence of alumina in combination with the oxides formed in-situ facilitated the formation of an oxidation film on surfaces, and effectively enhanced the charge transfer resistance of the coating, thereby significantly improving the corrosion resistance in seawater. Metallic Co was not only more easily oxidized but also more readily corroded than the alloyed Co. Compactness was identified as an important factor affecting CE resistance of coatings in deionized water, because defects facilitate the nucleation and eventual collapse of bubbles. Moreover, bubble collapse produced a transient high temperature spike in excess of 600 °C that also caused Co and Cr elements to oxidize. Because the CE tests were carried out in seawater, additional Co3O4 and Cr2O3 were generated owing to corrosion that more effectively increased the surface compactness and mechanical properties of the coatings. This behavior was particular notable for coatings with metallic Co and Cr, which should be why seawater corrosion could weaken the CE of Co-based coatings.