THE EFFECT OF POSTDEPOSITION HEAT-TREATMENT ON REACTIVELY SPUTTERED CRNX AND CR(N, O) COATINGS

Chromium nitride-based coatings, 3 mum thick, were deposited by reactive sputter deposition on polished AISI 304 stainless steel substrates. By varying the reactive gas content it was possible to produce coatings of various compositions, namely CrN, CrN0.55, and Cr(N, O) coatings. The corrosion resistance of these coatings was evaluated by measuring the anodic polarization curves in 0.5M H2SO4. Compared to the uncoated substrate a decrease in corrosion current density for approximately two orders of magnitude is obtained on coated samples. Postdeposition heat-treatment at 450-degrees-C in an oxygen flow for 24 h had a beneficial effect on the corrosion characteristics of the nitride coatings. Auger electron spectroscopy depth profiles revealed that postdeposition treatment induced the partial transformation of nitride to Cr-oxide and Cr oxynitride layers on the surface. The thickness of the Cr-oxide layer formed is dependent on the composition of the underlying nitride coating, increasing with decreasing nitrogen content.