From alloying to nanocomposites—improved performance of hard coatings

Nowadays a variety of different hard coatings are commercially available, the most widely used ones are TiN, TiC, TiCN, TiAlN, CrN, Al₂O₃, and combinations thereof, as well as some coatings with lubricating properties such as diamond-like carbon (DLC), WC/C or MoS₂. To fulfil the industrial demands for improved coatings, a lower friction, a longer lifetime, a desired biological behavior or a better thermal stability in different environments, improved and application adapted coatings are developed. The different properties of a coating can be tuned to a desired value by alloying with suitable elements. Composite materials such as multilayer coatings and isotropic nanocomposite coatings, having structures in the nanometer range, can even show properties which can not be obtained by a single coating material alone. The authors review research and development work on the improvement of the overall coating performance. It mainly addresses alloying, the development of multilayer systems and the recently emerged field of nanocomposite coatings.