Nowadays a variety of different hard coatings are commercially available, t
he most widely used ones are TiN, TiC, TiCN, TiAlN, CrN, Al2O3, and combina
tions 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 biolo
gical behaviour or a better thermal stability in different environments, im
proved and application adapted coatings are developed. The different proper
ties of a coating can be tuned to a desired value by alloying with suitable
elements. Composite materials such as multilayer coatings and isotropic na
nocomposite coatings, having structures in the nanometer range, can even sh
ow 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 coat
ings.