Investigation On Preparation And Anticorrosion/Antifouling Properties Of Thermal Sprayed Aluminium-based Composite Coatings

With the rapid development of the marine industry,marine corrosion and biofouling have drawn attentions of researchers.Surface treatment is one of the effective protection methods,including painting,electroplating,hot-dipping,thermal spraying,etc.Among these technologies,thermal spraying can provide a long-term protection for marine steel structures,and is thought to be one of the most competitive methods.Thermal sprayed aluminium?Al?coatings present good corrosion resistance due to their active chemical properties compared to marine steel structures.Therefore,thermal sprayed Al-based coatings can provide a cathodic protection for the steel structures.Meanwhile,the Al coatings can inhibit microbial adhesion through modifying the topological structures and chemical compositions of the surfaces of the coatings,thereby alleviating biofouling.However,thermal sprayed coatings also have its intrinsic defect,which is relative high porosity of coatings.Seawater can penetrate into the interface between coating and substrate through pores,thereby causing galvanic corrosion.Sealing is one of the commonly used methods due to low cost and easy operation.However,sealants always change the preset topological structures and chemical properties of the surfaces,finally damage the antifouling performances of the coatings.Therefore,new anticorrosion/antifouling coatings are expected for the marine environment.In this investigation,Al-polymer composite coatings were prepared using cored wires arc spraying.The microstructure evolution and corrosion resistance of the composite coatings were explored.The results show that three types of particles were formed during spraying:separated Al or UHMWPE particles,UHMWPE particles attached by Al particles and core-shell composite particles.The UHMWPE particles and UHMWPE particles attached by Al particles were completely melted and transformed to laminar structures distributed at the Al-Al interfaces.These laminar structures benefitted to improve the corrosion resistance of the Al-based coatings.The UHMWPE in the core-shell composite particles was protected by the external Al shell,and then remained the incompletely melted state in the coatings.These structures were lack of anticorrosion performances.Based on the above research,Cu nanoparticles?Cu NPs?were added into the Al-PMMA self-sealing coatings using cored wire arc spraying.The anticorrosion and antifouling performances of the composite coatings were investigated.The results show that the composite coatings presented an improved antifouling performance,and two antifouling mechanisms were explored.First,Cu²⁺were released into seawater and killed the bacteria.Meanwhile,oxidation of Al was accelerated due to Cu-Al galvanic reaction,and the needle-like corrosion products were formed,which pierced the cell membrane and killed the bacteria.The effects of dynamic adhesion and apoptosis processes of the bacteria on the electrochemical properties of the coatings were also evaluated.The results show that the dynamic adhesion and apoptosis behaviors of the bacteria enhanced the corrosion resistance of the coatings.Cold sprayed Al coatings present dense structures,thereby are able to used in the marine environment without sealing.However,cold sprayed Al coatings are lack of antifouling performances.Therefore,Ag nanowires?Ag NWs?fabricated using a hydro-thermal method were added in cold sprayed Al coatings.The effects of Ag NWs on the corrosion resistance and antifouling performances of the coatings were investigated.The results show that Ag NWs remained on the Al particles during spraying and deposited in the coatings due to van der Waals force.Ag NWs could effectively inhibit the formation of biofilm on the surfaces of the coatings,while not deteriorate the corrosion resistance of the coatings.