| Seawater is a very corrosive medium in nature,and most metal materials will corrode to varying degrees in it.However,titanium alloys have strong corrosion resistance in seawater due to their passivation characteristics.In recent years,the domestic shipbuilding industry and marine engineering have developed rapidly,and an increasing number of metal materials have begun to be used in ships and marine engineering,resulting in direct contact between various metal materials and titanium alloys,which has led to the serious galvanic corrosion occurred in low-potential metals.Therefore,it is of great significance to the long-term development of the shipbuilding industry to research the galvanic corrosion behavior between titanium alloys and other metals,and propose corresponding protection strategies to provide technical support for the design and application of dissimilar metal materials in ships.In view of the technical needs of metal materials for the development of marine ships in the future,this paper selected titanium alloy materials（Ti80）with good application prospects,representative marine pipeline materials（copper-nickel alloy B10）and hull structural materials（921A steel）as research targets.Electrochemical testing techniques such as polarization curve,electrochemical impedance spectroscopy,galvanic corrosion measurement and electrochemical noise were used to research the galvanic corrosion behaviors of titanium alloy/copper-nickel alloy（Ti80/B10）and titanium alloy/structural steel（Ti80/921A）couples in simulated seawater,and effect of different cathode/anode area ratios on galvanic corrosion.Meanwhile,scanning electron microscope（SEM）,X-ray energy dispersive spectroscopy（EDS）and X-ray photoelectron spectroscopy（XPS）were used to analyze the corrosion morphology and corrosion products.Based on the above results,the influence mechanism of Ti80 on the galvanic corrosion behaviors of B10 and 921A was researched and clarified.On this basis,according to the needs of galvanic corrosion protection,anodizing treatment and insulating coating were applied to the surface of titanium alloy,respectively.Scanning electron microscopy（SEM）,energy dispersive X-ray analysis（EDS）,X-ray diffraction analysis（XRD）,raman spectra and thermogravimetric testing（TGA）were used to characterize the coatings microscopically;Electrochemical test methods were used to evaluate its inhibitory effect and protective effect on galvanic corrosion of Ti80/B10 and Ti80/921A.The main research contents and findings were as follows:1.After being immersed in seawater for 2.5 hours,a dense film would be formed on the surface of Ti80,which increased the potential of Ti80.After that,Ti80 exhibited obvious galvanic corrosion acceleration effect on B10.For the Ti80/B10 couple,Ti80 significantly accelerated the corrosion rate of B10,and the degree of corrosion acceleration increased with the increase of Ti80/B10 area ratio.On the 28th day of corrosion time,When the area ratio of Ti80/B10 was（1/1）,（3/1）and（5/1）,the average galvanic current density was 3.6μA·cm-2,7.0μA·cm-2,8.5μA·cm-2,respectively;Whether B10 was coupled to Ti80 or not,its corrosion discipline was roughly similar.They all experienced the trend that the corrosion rate first decreased and then increased,and gradually stabilized in the later stage,and the corrosion current density of B10 was 3.3μA·cm-2;Coupling Ti80did not change the corrosion trend of B10.In the early stage of corrosion,the pitting corrosion trend of B10 was high,and with the increase of immersion time,the pitting corrosion trend decreased first and then increased.The corrosion product composition analysis on the surface of B10 by XPS showed that in the later stage,the surface corrosion products of B10 were composed of cuprous oxide and part of divalent copper,while in the deep layer,all of them were composed of cuprous oxide.The deep layer film had an excellent protective effect on B10.2.In the process of immersion in seawater,Ti80 always showed obvious galvanic corrosion acceleration effect on 921A steel.For the Ti80/921A steel couple,Ti80 significantly accelerated the corrosion rate of921A steel,and it also showed an obvious accelerated corrosion effect in the later stage,and the degree of corrosion acceleration increased with the increase of Ti80/B10 area ratio.On the 28th day of corrosion time,the area ratio of Ti80/921A steel was（1/1）,（3/1）and（5/1）,the average galvanic current densities were 1.8×101μA·cm-2,6.8×101μA·cm-2,7.0×101μA·cm-2,respectively.Whether 921A steel was coupled to Ti80 or not,its corrosion discipline was roughly similar.They all experienced the trend of increasing corrosion rate,and gradually became stable in the later stage,the corrosion current density of 921A was 1.25×101μA·cm-2;Coupling Ti80 did not change the corrosion trend of 921A steel,921A steel was uniformly corroded during the immersion period;Elemental analysis of 921A steel by EDS showed that the content of O and Cl elements on the surface of921A steel increased,indicating that the surface corrosion products were mainly iron oxides and chlorides,which could not effectively protect 921A steel.3.The surface of Ti80 was anodized to form an anodized film,and its inhibitory effect and protective effect on galvanic corrosion of Ti80/B10and Ti80/921A were studied.The results showed that when the anodic oxidation voltage was 50V,the current density of the anodic polarization curve(3.98×10-3μA·cm-2)of Ti80 was the lowest,the impedance modulus value（492.5MΩ·cm2）was the highest,and the surface had good barrier and protective performance;The galvanic current densities of anodized Ti80/B10 and Ti80/921A were 3.7×10-2μA·cm-2 and 2.7×10-1μA·cm-2,respectively,while the galvanic current densities corresponding to the unanodized Ti80/B10 and Ti80/921A couples were 2.6μA·cm-2 and8.5μA·cm-2,which were reduced by 70 and 31 times,respectively,indicating that the anodized Ti80 effectively reduced the galvanic current density between the couples,showing a certain galvanic corrosion inhibition and protection effect.4.Polydopamine-modified hexagonal boron nitride（h-BN@PDA）was added to epoxy resin coatings to manufacture insulating and anti-corrosion coatings.SEM scanning electron microscope and EDS elemental analysis showed that polydopamine was successfully coated on the surface of hexagonal boron nitride,which showed that the surface of h-BN became rough and the ratio of C element and O element increased;Raman spectroscopy analysis also verified this point of view,the new peak position of h-BN@PDA was caused by the deformation of catechol hydroxyl groups in polydopamine;Thermogravimetric analysis showed that the mass ratio of polydopamine in h-BN@PDA was 12%.The adhesion of the coating on the surface of Ti80 was 6.47MPa and the impact resistance was more than 50kg·cm2,which showed great comprehensive and mechanical properties.30-day salt spray corrosion test and electrochemical impedance spectroscopy results showed that surface corrosion product content of 0.5%（wt.%）h-BN@PDA epoxy coating was the lowest,and the impedance modulus value consistently exceeded1.4×1010Ω·cm2 during immersion,indicating that the coating had the best barrier and protective properties;The galvanic current densities of Ti80/B10 and Ti80/921A after coating were 3.9×10-2μA·cm-2 and 1.9×10-1μA·cm-2,respectively,compared to unanodized Ti80/B10 and Ti80/921A,which were reduced by 67 times and 44 times,respectively,indicating that the insulating anti-corrosion coating could effectively inhibit galvanic corrosion. |
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