Oxidation resistance of Cr1−xAlxN (0.18 ≤ x ≤ 0.47) coatings on K38G superalloy at 1000–1100 °C in air

Cr1−xAlxN coatings (0.18 ≤ x ≤ 0.47) were deposited on a Ni-based superalloy (K38G) by reactive sputtering method. High-temperature oxidation behavior of the coatings was investigated at 1000–1100 °C in air. The results indicated that the parabolic rate constants of Cr1−xAlxN coatings were much lower than that of the bare K38G alloy and the degree depended on the aluminum content of the coatings, demonstrating that this kind of coatings can effectively provide oxidation protection to superalloys in the temperature range of 1000 °C–1100 °C. The oxide scales consisted of a solid solution of (Cr,Al)2O3 and pure Cr2O3 grains dispersedly distributed in the outer oxide layer. Au marker experiments revealed that the oxidation of Cr1−xAlxN coatings proceeded mainly by inward diffusion of oxygen through (Cr,Al)2O3 scales. Meanwhile, outward diffusion of Cr ions also took place through short diffusion paths in the scales, resulting in formation of pure Cr2O3 grains on the outer layer of oxide scales.