By deposition of very different kinds of materials, the components (like Ti, Cr, Al in the first group, and Si in the other) are not mixed completely, and 2 phases are created. The nanocrystalline TiAlN- or AlCrN-grains become embedded in the amorphous Si3N4-matrix and the nano-composite structure develops.
Silicon increases the toughness and decreases the internal residual stress of the coating. The increasing of the hardness is generated by the structure only, the SiN matrix enwraps the hard grains and avoids growing of their size.
With the help of silicon the heat stability of Nanocomposites is extremely high, up to 1200 °C.