Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Wear-resistant Ti–B–N coatings have been deposited by reactive arc evaporation of Ti–TiB2 compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiBx phase mixture is observed at low N2 partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from -20 to -140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.