Arc-evaporated nanocomposite zirconium-based boronitride coatings

Nanocomposite nc-(Zr, Ti)(B, N)/a-BN coatings were deposited on AISI M2 HSS substrates by reactive arc evaporation of a composite target constituted of a Zr–ZrB2 (60–40 mol%) disc inserted into a conventional multiarc Ti target. The influence of the nitrogen flow rate and of the substrate bias voltage was investigated in relation to the chemical, structural, microstructural, mechanical and physicochemical features of the coating. It is shown that the coating hardness is a function of its composition, characterised by the (B + N)/(Zr + N) atomic ratio, and of the substrate bias which significantly modifies the nature of B–N bonds in the amorphous BN phase. Hence, coatings with about 50 GPa hardness and a low polar component of the surface energy (6.5 mJ m−2) can be deposited with intermediate nitrogen flow rate (15 sccm N2) and a significant bias of the substrate voltage (−200 V) which foreshadows future applications for anti-stick superhard coatings.