TiO 2 particle-polymer composite coatings were applied to the surface of a 5083 aluminum alloy. After using a knife to create an artificial defect, polarization resistance was monitored in artificial seawater at a temperature of 30 8C. The polarization resistance of the specimen coated with the composite polymer containing 3 vol% TiO 2 particles increased significantly over time, suggesting that the composite coating had self-healing properties. A carbon-containing 2-mm thick film was found on the coated aluminum substrate at the site of the artificial defect. The formation of the film was related to the dissolution of bisphenol A (BPA), which is a chemical precursor of the polymer coating that behaved as an inhibiting agent.

Hydrogen absorption into steel under an atmospheric corrosion condition is considered to occur because of the H + ion is reduced to hydrogen atom (H ads ) receiving electron formed by rust that forms by the corrosion reaction on steels. Thus, we investigated whether it is possible to reduce the amount of hydrogen absorption into steels by adding elements that improve corrosion resistance and control the formation of rust to reduce corrosion reaction. It was discovered that the amount of hydrogen absorption into steels can be reduced by adding elements that improve corrosion resistance and control the formation of rust on the surface of steels.KEY WORDS: high strength steel; delayed fracture; hydrogen embrittlement; diffusible hydrogen; atmospheric corrosion; amorphous rust.

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The effect of Ta addition on the pitting corrosion resistance of duplex stainless steels was investigated in both cases without and with deoxidization/desulfurization by the addition of Al and Ca. The pitting corrosion resistance was improved by the addition of Ta with two proposed mechanisms. For steels without Al and Ca, the MnS inclusions which act as initiation sites of the pitting corrosion are modified to the electrochemically-stable (Ta,Mn) oxysulfides. For steels with Al and Ca, the pitting initiation sites (CaS and (Al,Ca)oxides) are coated with the stable Ta-containing nitrides resulting in the suppression of pitting corrosion propagation.

The inclusion control is essential for the development of duplex stainless steels with high local corrosion resistance. In this study, the effect of the inclusion control by Ta addition on the crevice corrosion resistance of the super duplex stainless steels was investigated. The Ta-bearing super duplex stainless steels exhibited the higher crevice corrosion resistance compared to the super duplex stainless steels without Ta. In the super duplex stainless steels without Ta, the dissolution of MnS was observed after the crevice corrosion test, indicating that MnS acts as the initiation of the crevice corrosion. In the Ta-bearing super duplex stainless steels, part of MnS was modified to the (Ta, Mn)-oxysulfide which did not dissolve after the same crevice corrosion test as was conducted for the base alloy without Ta. This demonstrates that (Ta, Mn)-oxysulfide is electrochemically-stable. Thus, Ta addition to the super duplex stainless steel improved the crevice corrosion resistance because of a decrease of MnS which was modified to the electrochemically-stable Ta-containing inclusions.