High temperature oxidation of ion-plated CrN films
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The high-temperature oxidation of CrN films which were deposited onto stainless steel substrates using an arc ion plating apparatus was studied at temperatures ranging from 1023 to 1173 K for 0.6 to 480 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. Formed oxide layers were analyzed by XRD, SEM, and SAM. An activation energy of the oxidation of CrN was slightly lower than that of the self-diffusion coefficient of Cr ion in Cr 2 O 3 . It is concluded that the oxidation of CrN is controlled by the outward diffusion of Cr ions through the Cr 2 O 3 layer formed on each CrN grain.
I. INTRODUCTION The metallic nitride films such as titanium nitride have high hardness strengths and wear resistance. Therefore, these films have been applied extensively as the coatings on cutting tools, die molds, and so on. The performance of coated parts depends on not only mechanical properties such as hardness and friction coefficients, but also corrosion resistance of coated film. TiN and TiCN coatings deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) have been successfully applied in industrial usage for wear resistance, but they suffer from a limited oxidation resistance. To improve the high-temperature corrosion properties of TiN coating, Miinz,1 Freller and Haessler,2 and Ichimura and Kawana3 have studied the T i - A l - N films. They reported that oxidation resistance of T i - A l - N films increased with Al contents, 13 and the wear resistance by means of a drilling test was improved by Al incorporation.2'3 Ichimura and co-authors reported that the CrN film has high wear and corrosion resistance, which compared with TiN film.4'5 Recently, Navinsek and Panjan6 reported that the CrN coating has higher oxidation resistance compared with NiCr alloy and electrolytic hard chrome coating. However, the high-temperature oxidation mechanism of CrN is not clear yet. The purpose of this paper is to present the oxidation behavior of CrN film and to discuss the mechanism of the oxidation reaction.
a pressure of 10 5 Torr. The substrates were treated by metal ion bombardment to heat and remove the surface oxide layer. Chiba et al.4 reported that the phase of chromium nitride film deposited by arc ion plating varied with nitrogen gas pressure and substrate bias voltage. To prepare the single phase of CrN, nitrogen was introduced to maintain a chamber pressure at 50 mTorr during deposition. CrN films were deposited at the negative bias voltage of 300 V and the substrate temperature at about 600 K. The film thickness for oxidation kinetic experiments was kept about 4 ^ m by adjusting the coating time. The oxidation test was conducted as follows: the specimen was kept in a platinum basket and set in the electric furnace with an air flow of 500 cm 3 /min. The samples were heated at temperatures ranging from 923 to 1173 K for 0.6 to 480 ks. After each oxidation period, samples were taken from the furnace and the weight change was measured
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