Effect of plasma nitriding on hydrogen behavior in electroplated chromium coating

The phase composition and hydrogen behavior in coatings produced on Armco i ron by electrochemical deposition of chromium (Cr) and subsequent plasma-as sisted nitriding were investigated. At cathodic Cr deposition, no hydrogen charging of the iron substrate occurs. The amount of hydrogen absorption wi thin the Cr coating (50 mum thick) was measured as high as 450 ppm. Plasma- assisted nitriding of a galvanic Cr coating caused the formation of a surfa ce layer consisting of compact nitrides (Cr2N + CrN) and precipitates of ni tride within the bulk of the Cr coating and a (Cr,Fe) alloy layer between t he chromium coating and the steel substrate. The compact nitride layer prev ented hydrogen escape from the Cr coating. The nitride precipitates served as hydrogen traps, and thus hampered hydrogen desorption. Hydrogen-assisted phase transformations in nitrided electroplated Cr coating were observed a nd are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.