The Effect of Sealing Treatment on the Corrosion and Erosion-corrosion of High-velocity Oxy-fuel Fe-based Amorphous Coating

Author:Liu Ming Ming

Supervisor:zheng yu gui hu hong xiang


Degree Year:2019





Coating protection is one of the most common methods of keeping metal materials from corrosion.However,it will inevitably introduce porosity and defects,which directly affect the coating’s properties.Therefore,it is necessary to seal coatings to improve their corrosion resistance.Sealing treatment refers to the method of soaking,brushing and so on to make the penetration of sealants into the coating porosity as deep as possible.It can reduce coating’s porosity and shield the corrosion medium,which can improve the corrosion resistance of the coatings.Fe-based amorphous coatings show particular attraction because of high strength,high hardness,good wear resistance and corrosion resistance,but the inevitable porosity defects directly affect their service lives.In this thesis,the Fe-based amorphous coating was taken as the representative of the coating with porosity defects.The corrosion and erosion-corrosion performances of the sealants,sealing technologies,et al.were systematically studied by means of electrochemical testing methods,scanning electron microscopy,electron probe micro-analyzer,Fourier transform infrared spectroscopy,etc..It is intended to guide the selection of the sealants and promote practical application of sealants.The main results of this study are summarized as follows:Three sealed coatings including sol-gel(SG)coating,sol-gel with cerium nitrate(SCN)coating and sol-gel with cerium tartrate(SCT)coating were applied on Fe-based amorphous coating.Their corrosion resistance was in order of SCT coating,SG coating and SCN coating.The SCT coating showed the best corrosion resistance among three sealed coatings.It was resulted from the higher shielding performance due to the low solubility of cerium tartrate as filler to sol-gel sealed coating.Moreover,a combined inhibition effect of cerium tartrate composed of cerium ions and tartrate groups also played an important role in increasing the coating’s corrosion resistance.A modified epoxy sealant loaded with the montmorillonite was successfully prepared.The filler montmorillonite was firstly modified by octadecylamine and then intercalated with 2-mercaptobenzimidazole(OMM).A comparison in the corrosion resistance between the blank epoxy sealant and the modified epoxy sealant was performed.The results showed that OMM-coating exhibited the best long-term corrosion resistance.It was attributed to the change of the polarity of the filler montmorillonite.And the layer spacing became larger with a thin layer structure which could improve the shielding performance of OMM-coating.In addtion,the corrosion inhibitor between the montmorillonite interlayer could be released by ion exchange and migrated to the corrosion active region for corrosion inhibition.Three sealing methods including conventional impregnation sealing(CIS),ultrasonic excitation sealing(UES)and vacuum sealing(VS)were employed to seal the Fe-based amorphous coatings.The results showed that the long-term corrosion resistance of three sealed coatings was UES coating>CIS coating>VS coating.Among them,UES coating showed the best long-term corrosion resistance,which was attributed that ultrasonic energy benefited the escape of the air in the pores,reduced the penetration reaction force of sealant,and further promoted the penetration of more sealants to the pores.The effects of epoxy sealing treatment,stearic acid sealing treatment,aluminum phosphate sealing treatment and cerium salt sealing treatment on the erosion-corrosion resistance of Fe-based amorphous coatings were evaluated by coating impedance,surface morphology and roughness.A home-made rotating disc instrument was employed to simulate the dynamic seawater environment.The results showed that aluminum phosphate sealed coating displayed the best erosion-corrosion property,followed by epoxy sealed coating,stearic acid sealed coating and cerium sealed coating.Aluminum phosphate sealant has the best sealing effect because of the high permeability depth of aluminum phosphate sealant and the high hardness of the sealed layer.