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ma ich 0-C n (X when compared to single layer nitride coatings [1–7]. top of films [13–15]. As a result, thermal stability plays an important role in the performance of coated tools operated at CrN [18]. This study was mainly focused on the thermal CrN and multilayered CrN/AlN coatings with different modulation periods were deposited on silicon substrates by m and aluminum Thin Solid Films 494 (200elevated temperature in either vacuum or air. CrN films,Although multilayer coatings can possess high hardness at an ambient temperature, heat treatment at elevated tempera-tures in vacuum has been reported to degrade the strength of multilayer coatings leading to failure. This is a critical issue which is caused by the disappearance of the nano-layered structure due to the inter-diffusion of atoms [8–12]. It was also found that when annealed in air, the hardness of the multilayer coatings was reduced even below the hardness of the rule of mixtures because of significant oxidation on the stability of CrN and CrN/AlN coatings with modulation periods of 4 nm and 20 nm in both vacuum and air environments. Comparison between coatings at vacuum and air will be discussed. The microstructure of CrN and CrN/ AlN coatings were analyzed by X-ray diffraction, SEM and TEM. Nanoindentation tests were used to investigate the hardness of the films deposited under various conditions. 2. Experimentalcoatings was better than that of CrN coating. The hardness degradation ratio of CrN/AlN coating with modulation period of 4 nm was only 8.1 % at 700-C, which was superior to that of a simple CrN coating