Metastable cubic (c) AlCrN coatings decompose during thermal annealing into their stable phases Cr and hexagonal (h) AlN under the release of N 2. We show that the onset temperature To and amount of N2 release depend on the ambient atmosphere. For c-Al 0.56Cr0.44N only a partial dissociation into h-AlN and h-Cr2N with To ∼ 1180°C occurs during annealing in N2 up to 1450°C. Experiments in synthetic air to 1450°C yield a complete oxidation to (Al0.56Cr0.44) 2O3. © 2008 IOP Publishing Ltd.