Study On Anti-corrosion Properties Of Monel K-500 Alloy In The Sea

As one of significant marine materials,Monel K-500 alloys,were widely used as propellers,pump shafting,bolts and other components,of which corrosion mechanism were the foundation to guide its proper usage.As Monel K-500 mainly happened to erosion-corrosion and pitting corrosion in the marine environment,so four experiments ncluding pipe flow test,jet tst,micro-electrochemistry test and electrochemical test,were apopted to study the characteristics and influencing factors of those.Erosion-corrosion properity of Monel K-500 alloy at 3 m/s in the seawater with no sand was reserched through the tube test.It was found that the linear polarization method could be used as an in situ and rapid method monitoring the erosion-corrosion degree of the Monel K-500 alloy,and it was with good anti-corrosion properities combining with the composition and morphology results,of which corrsion rate was about 0.004 mm/a.XPS results showed that the passivation film was composed of Ni O,Cu₂O and Cu O,and Fe atoms could be dissolved into the Cu₂O vacancy,which further improved the passivation film density.It was indicated that the content of gravel was the main reason of the erosion-corrosion alloy,which had a more important effect on the properities of erosion-corrosion than the change of velocity.The impact angle had little effect on the character of erosion-corrosion and cutting effect of gravel was most harmful,for which easily forming a horseshoe pit in the surface of alloy and furrows.Distribution and variation of surface potential of Monel K-500 alloy in seawater were studied by micro-electrochemistry experiment.It was indicated that although pitting occurs in seawater,it grew relatively slowly,which was mainly related to the high self-repair capability of Monel K-500 alloy.After pitting initiation,the lowest potential value would transfer from the center of pitting to its boundary area,of which expansion rate declined even further in the depth direction.It was suggested that the pitting corrosion of Monel K-500 was related to the presence of Ti C,and the higher the content of Ti C,the weaker the pitting corrosion resistance.Through the electrochemical test,it was shown that the pitting corrosion tendency of the alloy increased with the increase of both chloride ion concentrationand temperature and the decrease of p H.Meanwhile,the logarithm of chloride ion concentration and the pitting potential basically met the linear relationship,and the temperature and the pitting potential basically followed the linear relationship.