Ceramic coatings by physical vapour deposition

The surface properties of a component can now be tailored to be independent of those of the bulk material by the use of surface engineering. This paper reviews a number of the deposition techniques available for the laying down of ceramic coatings, and describes in some detail physical vapor deposition (PVD) methods which are divided into two broad classes: sputtering and evaporation dependent processes. The basic principles on which each class of process is based are reviewed and the general subject area of PVD technology is discussed in terms of the commercially available equipment and the critical process parameters which can often influence end-user applications. The ability to deposit high-quality ceramic coatings by a range of techniques has led to the development of methods for characterizing the basic properties of the coating/substrate system. Of these hardness, residual stress and adhesion are most relevant to a wide range of applications, and progress in the measurement of these fundamental properties of the coating/substrate system is reviewed and the application areas for thin ceramic coatings discussed. The paper concludes by highlighting the key areas where further research is needed, both in terms of process technology and in the development of new coating compositions and formulations. These requirements are judged against titanium nitride, which is the accepted benchmark for many tribological applications.