High temperature oxidation behavior of CrN/AlN superlattice films

Abstract

The oxidation behavior of CrN/AlN superlattice films with different bilayer periods (Λ), Al/(Cr + Al) ratios, and crystal structures of the AlN layer was investigated. The films were deposited using a pulsed dc closed field unbalanced magnetron sputtering system. The oxidation tests were carried out in the ambient air at elevated temperatures from 700 to 1100 °C for 1 h. The changes in the crystal phase, microstructure and hardness of the films after the oxidation tests were characterized using X-ray diffraction, scanning electron microscopy and nanoindentation, respectively. When both CrN and AlN layers were in the NaCl cubic structure, the film with Λ = 3.8 nm and an Al/(Cr + Al) ratio of 0.6 exhibited a superior oxidation resistance than the film with Λ = 12.4 nm and an Al/(Cr + Al) ratio of 0.19. The film with Λ = 3.8 nm maintained the nanolayered structure with an oxidation temperature up to 1000 °C by the protection of a thin and dense X-ray amorphous oxide layer. In contrast, when the AlN layers were in the Wurzite hexagonal structure, the film with Λ = 22.5 nm and an Al/(Cr + Al) ratio of 0.67 exhibited poor oxidation resistance. The film lost the superlattice structure at 800 °C and was completely oxidized at 1000 °C due to the formation of a porous crystalline oxide layer on the surface.