Superhard nc-TiN/a-BN and nc-TiN/a-TiBx/a-BN coatings prepared by plasma CVD and PVD: a comparative study of their properties

We present a comparative study of the preparation and properties of superhard ‘Ti–B–N’ coatings deposited by plasma CVD and by Vacuum Arc Evaporation (PVD) of Titanium combined with Plasma CVD of TiB2 and BN. Using high frequency plasma CVD at a total pressure of several mbar with TiCl4, BCl3, N2 and H2 as reactants, superhard (HV≈40–50 GPa) nanocomposite coatings were successfully and reproducibly deposited and characterized in terms of mechanical properties (indentation and scanning electron microscope (SEM)), phase composition (X-ray photoelectron spectroscopy and elastic recoil detection) and nanostructure (X-ray diffraction, SEM). Using reactive sputtering, several authors reported about the preparation of superhard TiN/TiB2 coatings with only a small fraction of BN. Efforts to increase the fraction of the BN phase resulted in soft films. In contrast, plasma CVD yields superhard nc-TiN/a-BN and nc-TiN/a-TiB2/a-BN coatings in a wide range of the fractions of BN and TiB2 phases. This is attributed to the high chemical activity of nitrogen under the conditions of plasma CVD. Industrial scale vacuum arc evaporation PVD in combination with plasma CVD is used for preparation of ‘Ti–B–N’ coatings. In the system nc-TiN1−x/a-TiB2 with a minor fraction of the a-BN phase superhard coatings with a very low fraction of microparticles and resultant low surface roughness of Rm≈0.15 μm were successfully prepared and those are intended for testing under a variety of cutting conditions.