Combining thermal spraying and PVD technologies: A new approach of duplex surface engineering for Ti alloys

Abstract

There is a rapid growth in demand for improved surface performance in many priority industrial sectors. There have also been rapid developments in methods of surface engineering and in tribological understanding. There is accordingly an exciting opportunity for cost effective industrial exploitation of materials with desirable properties. Among these materials, titanium and its alloys occupy an important place: they are very promising candidates for an increasing number of industrial applications, provided some weak points are solved, as tribological performances.The present work aims at overcoming the above-mentioned limitations by developing an innovative surface treatment, consisting of two consecutive phases: deposition by reactive plasma spraying (RPS) of a thick (hundreds of micrometres) composite Ti/TiN coating on the titanium based substrate and deposition by physical vapour deposition (PVD) of a thin, hard, TiN coating, on the already deposited thick coating.With the proposed coating system, the deposition of the Ti/TiN interlayer can limit the deformation of the system, reducing the abrupt change in properties at the substrate/coating interface, minimising the effects due to the mechanical response. The low friction TiN coating used as top layer not only increases the wear resistance but also decreases interfacial shear stress, reducing the probability of debonding.The present work is divided in three parts: in the first one already published results on the duplex RPS+PVD coating setting up will be resumed; in the second one, original results on the tribological behaviour of such a coating will be presented; finally, the coating and testing of a real component will be shown.