Some consequences of the partial crystallographic coherence between nanocrystalline domains in Ti–Al–N and Ti–Al–Si–N coatings

Formation of partially coherent nanocrystalline domains, development of intrinsic residual stresses and the relationship between the partial coherence of crystallites and the hardness of vacuum-arc-deposited Ti–Al–N and Ti–Al–Si–N nanocomposites were investigated for different chemical compositions of the nanocomposites using a combination of the electron probe microanalysis, X-ray diffraction, transmission electron microscopy with high resolution and hardness measurement. Partial coherence of nanocrystalline domains was found to be a very important microstructural feature, which is strongly related to the correlated orientation of neighbouring crystallites and to the atomic ordering at the crystallite boundaries. Appropriate mutual orientation of neighbouring crystallites and suitable atomic ordering at the crystallite boundaries facilitate the development of intrinsic residual stresses, which influence directly the hardness of the nanocomposites.