CORROSION BEHAVIOR OF CHROMIUM NITRIDE FILMS PRODUCED BY REACTIVE ION PLATING IN SULFURIC-ACID-SOLUTION

Chromium nitride films were deposited on glass substrates by r. f. reactive ion plating, and the deposition rate, the structure and the corrosion resistance of the films were investigated. The deposition rate increased, but the nitrogen content of the nitride film tended to decrease with increasing the current of electron beam for evaporating chromium at a constant nitrogen pressure. X-ray diffraction showed that the film was a solid-solution of Cr and N (alpha-Cr) at the current of 100 mA, a mixture of Cr2N and CrN at 60 mA, and a single phase of CrN at 10 approximately 50 mA. The decrease in current led to a transformation in the film structure; a structured film changed to a nearly amorphous, dense film with a smooth surface, and a great improvement in the corrosion resistance. The Cr and alpha-Cr film were rapidly corroded in 1 kmol.m-3 H2SO4 at 373 K, while the single phase of CrN hardly corroded. On the mixture of Cr2N and CrN, the Cr2N was selectively corroded and the amount of dissolved chromium was about two orders of magnitude larger than that for the single phase of CrN. The films deposited with low electron beam current were bent due to the difference in the thermal expansion between the film and the substrate, and some of them were peeled off during the corrosion test.