Structure, hardness and thermal stability of TiAlBN coatings grown by alternating deposition of TiAlN and BN

Hardness and thermal stability of TiAlBN coatings prepared by alternating deposition of TiAlN and BN with high rotation speed of substrate holder (∼7 rpm) have been investigated. The TiAlN and BN were deposited by reactive sputtering of Ti0.5Al0.5 and BN targets with N2 and Ar reactive gases, respectively. Despite alternating deposition, the TiAlBN coating did not show layered structure due to high rotation speed of substrate holder. By TEM analysis, the TiAlBN coating was observed to be nanocomposite with grain less than 10 nm in size. Compared to TiAlN coating, the TiAlBN nanocomposite coating showed superior hardness. Furthermore, the hardness of the coating increased after the heat-treatment in N2 atmosphere up to 800 °C. By comparison with TiAlN/BN nanoscale multilayered coating prepared by the same deposition method except the lower rotation speed of substrate holder (∼1 rpm), the hardness enhancement after annealing, 'self-hardening', of the TiAlBN nanocomposite coating is believed to be due to the sharpness in chemical composition at the interface between TiAlN and BN phase.