Impact of CrAlN Coatings on Oxidation Behavior of K38G Alloy at 800 and 900°C

CrAlN coatings have been deposited on K38G alloy by Closed Filed Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The microstructure, surface and section morphology of CrAlN coatings before and after oxidation were analyzed by XRD and SEM. At the same time, the mechanical properties and oxidation resistance of CrAlN coating were also studied. The results indicate that the phases in the isometric crystal CrAlN coatings with a hardness of 3500 HV and a adhension of 20 N was the coexistence of CrN and AlN. Each element of CrAlN coatings still existed at 800 and 900°C, but it demonstrated better high-temperature oxidation resistance because of denser oxide scale at 800°C. Besides, internal oxidation occurred under the two temperatures.

Effects of Water Vapor on the Oxidation Behaviors of Cr-Al-N Coatings

Cr1-xAlxN coatings with different aluminum content were deposited on K38G alloy by reactive magnetron sputtering method. Oxidation behaviors of these coatings were investigated at 1000°C in air+10 vol.% water vapor. The surface morphologies and the microstructure of the oxide scales were analyzed by SEM and XRD, respectively. The results showed that the oxidation of the Cr1-xAlxN coatings in the wet air also obeyed the parabolic law; however, compared to that in the dry air, existing of 10 vol. % water vapor increased the parabolic rate constants of the coatings. It was believed that the accelerating of the oxidation rates was owing to easily outwards diffusion of Cr through the looser and coarser oxide scales formed on the surface of the coatings when oxidized in wet air.