Properties of superhard nc-TiN/a-BN and nc-TiN/a-BN/a-TiB2 nanocomposite coatings prepared by plasma induced chemical vapor deposition

Using high frequency plasma chemical vapor deposition (P CVD) at a total pressure of several mbar with TiCl4, BCl3, N2 and H2 as reactants, superhard nanocomposite nc-TiN/a-BN and nc-TiN/a-BN/a-TiB2 coatings with hardness of 40–50 GPa were reproducibly deposited and characterized in terms of their phase composition, nanostructure, thermal stability, oxidation resistance and mechanical properties. By analogy with earlier studied systems nc-MnN/a-Si3N4 (M=Ti, W, V) and nc-TiN/a-Si3N4/a- and nc-TiSi2, the maximum hardness of the nc-TiN/a-BN and nc-TiN/a-BN/a-TiB2 coatings was obtained at the percolation threshold when there is about one monolayer of thin continuous tissue of a-BN between the TiN nanocrystals. It was shown that the thermal stability and oxidation resistance of these coatings is fairly high but lower than that of the nc-TiN/a-Si3N4 and nc-TiN/a-Si3N4/a-TiSi2 coatings.