Studies on a combined reactive plasma sprayed/arc deposited duplex coating for titanium alloys

A new type of duplex layered coating especially developed for titanium alloys is described in this paper. This coating comprises a combination of a graded thick TixNy-based coating and a thin TiN top coat. The graded coating was obtained by reactive plasma spray (RPS) deposition of a Ti–4,5Al–3V–2Mo–2Fe powder onto a Ti6Al4V alloy substrate under an N2 atmosphere. Such a coating consisted of a Ti matrix with dispersions of TixNy phases and the other elemental species contained in the powder alloy composition. The top thin film was deposited by a physical vapour deposition (PVD)-arc technique and it was comprised of stoichiometric TiN. verified by SEM studies that the porosity of the RPS coatings was drastically reduced after the PVD deposition. A study of the various steps of the coating system production process suggested that titanium oxynitrides were primarily responsible for the filling of the pores and that their formation was triggered by the energy of the metal ionic bombardment and the presence of oxygen inside the cavities of the RPS coatings. The resultant duplex coating has excellent mechanical and adhesion properties.