Oxidation of arc ion-plated CrN coatings at elevated temperatures

Characterization of the CrN coatings oxidized in air at temperatures ranging from 300 to 800degreesC for 60 min was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Auger electron spectroscopy (AES). The CrN coatings were prepared by cathodic arc ion plating deposition on a type AISI 304 stainless steel with a Cr interlayer. XRD result shows that oxidation of the CrN-coated steel above 500degreesC produces two new phases, Cr(2)O(3) and beta-Cr(2)N, and the amount of both phases increases with the oxidation temperature. A noticeable change in the surface morphology of the coatings was observed by SEM in the specimens oxidized at temperature above 600degreesC. Cross-sectional TEM reveals that oxidation of the CrN-coated steel at high temperatures produces an oxide layer, Cr(2)O(3), on the coating surface, and the underlayer is a mixture of CrN and beta-Cr(2)N phases. Unlike the as-deposited specimen, the dual-phase layer in the oxidized specimens has an equiaxed grain structure and the average grain size of the layer increases with oxidation temperature. Auger depth profiling of the oxidized CrN coatings at various temperatures reveals the elemental distributions in the coatings and the thickness of the oxide layer near the free surface, from which the activation energy of oxidation for the CrN coatings is calculated to be 1.63 eV. (C) 2002 The Electrochemical Society.