This diploma thesis focuses on microstructure-related diffusion processes in selected arc evaporated face centered cubic (fcc) Ti-, fcc Cr- and hexagonal closed packed (hcp) Al-based nitride coatings, which are used as wear protective coatings for cutting processes. A comparative study of fcc Cr1-xAlxN (x=0, 0.7), fcc Ti1-xAlxN (x=0, 0.5, 0.6) and fcc TiCN coatings on cutting tools showed surprisingly superior wear behavior predominantly of the conventional coating systems, i.e. TiN and TiCN. The reason for that was found in diffusion processes at the elevated temperatures of cutting, contributing to degradation of the coating structure and thus to deteriorating cutting performance. In order to study diffusion processes in these coatings, coated high speed steel substrates were annealed at Ta=900, 1000, 1100, 1200 °C in vacuum for 3 hours and the elemental and phase composition of the coatings was subsequently studied by a combination of X-ray diffraction and backscattered electron imaging, elemental mapping with qualitative linescans and quantitative energy-dispersive X-ray spectroscopy. It is explained how diffusion processes are related to the decomposition routes of the metastable coatings, which are associated with the generation of diffusion paths promoting transport of elements through the coating. This is highly pronounced in metastable TiAlN, which decomposes to thermally stable hcp AlN and fcc TiN. Even much stronger diffusion is present in coatings undergoing two-step decomposition processes. This is typical for the metastable fcc CrAlN, which decomposes to thermally stable hcp AlN but unstable fcc CrN, which in turn decomposes further to Cr2N and Cr due to the release of weakly bonded N. This results in generation of efficient diffusion paths. On the other hand, the thermally stable TiN, TiCN or AlN represent effective diffusion barriers with only limited diffusion processes predominantly at the grain boundaries.