Structure–property–performance relations of high-rate reactive arc-evaporated Ti–B–N nanocomposite coatings

This study demonstrates the successful synthesis of hard and wear resistant nanocomposite Ti–B–N coatings by high-rate reactive arc-evaporation from Ti/B compound targets in a commercial industrial-sized deposition chamber. Morphological investigations by profilometry and scanning electron microscopy indicate that the coatings exhibit a lower droplet density as compared to a TiN reference as well as a compositionally graded multilayer structure. These results will be related to the previously reported microstructural characterization, which revealed a highly stressed nanocrystalline TiBN solid solution formed at lower N2 fractions and a stable TiN/(amorphous) BN dual-phase structure obtained at higher N2 partial pressures. Emphasis is further laid on mechanical and tribological characterization. A maximum hardness of 34.5 GPa is detected for the TiBN solid solution decreasing to 24 GPa for the coatings containing approximately 30–40 vol.% amorphous BN. The maximum in hardness coincides with the minimum in wear, while the coefficient of friction is fairly constant at 0.7–0.8.