Characterisation of reactively sputtered Ti–B–N and Ti–B–O coatings

The effect of oxygen or nitrogen incorporation into sputtered titanium–boron based coatings was investigated. The coatings are deposited by reactive magnetron sputtering of a TiB2 target in Ar–N2 or Ar–O2 mixtures. The composition, structure, hardness and electrical resistivity of these films were compared. Ti–B–N films crystallise in a TiB2-like structure at low nitrogen flow rate (Q(N2)) and in a TiN one at high Q(N2). Whatever Q(N2), BN bonds are detected by Fourier transform infrared spectroscopy. Then, Ti–B–N films are nanocomposite coatings: nc-TiB2/a-BN and nc-TiN/a-BN vs. Q(N2). On the other hand, grazing angle X-ray diffraction and X-ray photoelectron spectroscopy analyses show that Ti–B–O films are nanocomposite coatings at low oxygen flow rate (i.e. nc-TiB2/a-oxides) and become amorphous for higher oxygen content. For both systems, the hardness of the films decreases when the reactive gas flow rate increases. Highly oxygenated Ti–B–O films are electrical insulators whereas highly nitrided Ti–B–N films conserve their metallic character.