Recent developments in the deposition of c-BN coatings

Cubic boron nitride, c-BN, due to the high strength of its covalent inter-atomic bond, small bond distance, and high coordination number, is the second hardest (HV ≈ 50 GPa) material (the first is diamond with HV ≈ 70 – 90 GPa) available as single crystal. The fact that c-BN does not react readily with ferrous metals, cobalt and nickel; can be deposited in thin film form under standard conditions (1 bar, 298 K); and has a high resistance to oxidation in air to high temperatures of 1000°C, makes it very attractive for tool applications. Unfortunately c-BN films due to high compressive stress, which can reach values up to 25 GPa and poor adhesion strength of the interface, still reveal themselves to be poor adherent to almost every substrate material