Surface modification of type 304 stainless steel with duplex coatings for corrosion resistance in sea water environments

An attempt was made to improve the localised corrosion resistance of AISI type 304 stainless steel by modifying the surface with duplex coating (titania over ceria). Simple chemical immersion method was adopted for ceria coating, whereas sol-gel route with dip coating method was followed for titania coating. The adherence of the coating was evaluated by ASTM D3359 standard, and the composition of the duplex coatings was evaluated by X-ray photoelectron spectroscopy. The experimental parameters, namely, bath composition, temperature, immersion time and withdrawal speed of the specimens, were optimised to get homogeneous adherent coating. The localised corrosion resistance of ceria, titania and duplex coatings in sea water was studied by potentiodynamic anodic polarisation experiments. These coatings were characterised also by optical and scannning electron microscopes for analysing their pit morphologies. Duplex coated 304 SS exhibited superior corrosion resistance, and the probable reason for the improvement is discussed in detail in this investigation.