ELECTROCHEMICAL AND LONG-TERM CORROSION STUDIES OF SEVERAL ALLOYS IN BARE CONDITION AND PLASMA SPRAYED WITH CR2O3

The corrosion resistances of 13 alloys including several 300 series stainless steels, with and without a chromium oxide coating deposited by plasma spray, were evaluated in chloride-containing aqueous environments. Short-term electrochemical tests were used to evaluate the pitting corrosion resistance of bare alloys and the crevice corrosion resistance of the alloys with the coating. Salt spray immersion tests were conducted to evaluate the long-term corrosion behavior. The coated samples used in this study were not sealed. Results of the short-term electrochemical corrosion tests were found to be very consistent with the long-term corrosion data. All 300 series stainless steels together with several other alloys were found to be susceptible to pitting and crevice corrosion. Stainless steels such as Ferralium 225R, 20Mo-6TM and 7-Mo Plus(TM) were found to have good resistance to crevice corrosion. (Ferralium 255 is a registered trademark of Haynes International, Inc. 20Mo-6 and 7-Mo Plus are trademarks of Carpenter Technology, Inc.) The Inconel 625 (IN 625) and Ti-6Al-4V alloys were found to have the highest corrosion resistances of all the alloys evaluated. The chromium oxide coating did not show any significant corrosion.