AVS 49th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE+NS-TuM

Invited Paper SE+NS-TuM3
Nanocomposite and Nanolayered Hard Coatings

Tuesday, November 5, 2002, 9:00 am, Room C-111B

Session: Nanocomposite and Nanolayered Coatings
Presenter: J. Patscheider, EMPA, Switzerland
Authors: J. Patscheider, EMPA, Switzerland
T. Zehnder, EMPA, Switzerland
J.C. Cancio, EMPA, Switzerland
Correspondent: Click to Email
Nanostructuring of hard coatings, which is achieved by combining two phases with atomically sharp interfaces, opens up new possibilities to improve conventional coatings with respect to their hardness, limited temperature stability and their frictional behavior. The best known combinations of well-separated phases for increased hardness are multilayered superlattices as well as nanocomposite coatings. Nanocomposite coatings proved successful in promoting hardness, oxidation resistance, improved wear behavior and other properties relevant for protective coatings. Such coatings are composed of nano-crystalline grains of transition metal nitrides or carbides, which are surrounded by amorphous hard matrices. Most nanocomposite hard coatings show typically a maximum of the hardness, which can range from 30 GPa to reported values above 60 GPa, as the composition is changed from the pure crystalline phase (no amorphous component) to compositions dominated by the amorphous phase. At the hardness maximum the domain size of the nanocrystalline phase is below 10 nm and the amorphous layer separating the nanocrystals, is only a few atomic bond lengths thin. A comparison to hadness-enhanced superlattices show that the critical dimensions necessary to obtain this effect are of the same order, i.e. the domain size in hard nanocomposites and the single layer thickness in superlattices are both below 10 nm. Due to the absence of dislocation activity, deformation of nanocomposites will be only due to grain boundary sliding. This process requires more energy than deformation by dislocation movement, which is synonymous to increased hardness. In some cases the amorphous phase can act as a solid lubricant (a-C or a-C:H) or as diffusion barriers (Si@sub 3@N@sub 4@) for improved thermal stability. The amorphous phases in nanocomposites thus cause, apart from the enhanced hardness, additional effects that are beneficial for the performance of these new wear-protective coatings.