XRD and XPS study on reactive plasma sprayed titanium–titanium nitride coatings

Reactive plasma spraying of titanium in a nitrogen-containing plasma gas allows the formation of hard titanium composite coatings reinforced by in situ formed titanium nitrides (TiN and Ti2N). In the present study, the formation of titanium nitrides during the reactive spraying of titanium was studied by means of two different analysis techniques: X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The diffusion and solidification sequence predicted by the Ti-N phase diagram was consistent with the experimental results. The nitrogen retained in the coating was found mainly as titanium nitrides and not as interstitial nitrogen in the titanium lattice. It is hypothesised that the formation and direct solidification of TiN occurs during the flight of the sprayed particles. The presence of solid TiN constrains the thermal contraction of titanium splats upon solidification. The observed cell distortion of the residual α-Ti is thus attributed to tensile stresses arising from the solidification process.