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

Reactive plasma spraying of titanium in a nitrogen-containing plasma gas al lows the formation of hard titanium composite coatings reinforced by in sit u formed titanium nitrides (TiN and Ti2N). In the present study, the format ion of titanium nitrides during the reactive spraying of titanium was studi ed by means of two different analysis techniques: X-ray diffraction (XRD) a nd X-ray photoelectron spectroscopy (XPS). The diffusion and solidification sequence predicted by the Ti-N phase diagram was consistent with the exper imental results. The nitrogen retained in the coating was found mainly as t itanium nitrides and not as interstitial nitrogen in the titanium lattice. It is hypothesised that the formation and direct solidification of TiN occu rs during the flight of the sprayed particles. The presence of solid TiN co nstrains the thermal contraction of titanium splats upon solidification. Th e observed cell distortion of the residual alpha -Ti is thus attributed to tensile stresses arising from the solidification process. (C) 2001 Elsevier Science B.V. All rights reserved.