Coatings of c-BN, c-BN-based metastable
materials and c-BN- based nanocomposites
S. Ulrich, J. Ye, M. Stüber, H. Leiste,
Forschungszentrum Karlsruhe, IMF I, Postfach 3640, D-76021 Karlsruhe,
Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen
eingeladener
Vortrag, 6th HIPIMS Conference 2009, Sheffield, UK, 01.-02.07.2009
Improvement
of tools and diverse mechanical parts by means of wear-protective hard surface
coatings has become in the past years an indispensable industrialized routine
of enormous economical and ecological significance. High-performance surface
coatings, often demanded in sophisticated profiles with respect to their
physical and/or chemical properties, are now ever more anticipated by
industries. A powerful hard coating has thus to exhibit together with its
outstanding hardness an optimized spectrum of other properties dictated by
individual applications. The anticipated coating properties may typically
include: (a) good toughness, (b) excellent wear resistance, (c) thermal and
chemical stability, (d) good adhesion on the substrate, and so forth. To
realize these manifold, sometimes even appearing conflicting requirements, a
proper design of coating constitution, often scaling down to nanometer scales,
is obligatory. For resistance against abrasive-wear, covalent-bond dominated
superhard materials are particularly suitable which diamond and cubic boron
nitride (c-BN) belong to [1]. c-BN outperforms in comparison with diamond,
especially in many harsh service conditions, on account of its good oxidation
resistance, thermal stability, as well as chemical inertness with respect to
ferrous alloys for temperatures up to 1000°C. As with diamond, the high thermal
conductivity of c-BN enables an effective dissipation of heat as generated
during service of tools and mechanical parts. This paper reviews the
fundamental parameters that are critical to the nucleation and growth of c-BN.
Various surface kinetic processes and their consequences are discussed, in
particular with reference to the resulting film phases and stress. Individual
mechanisms are then summarized aiming at the reduction of detrimental film
stress. Furthermore, available techniques useful for the growth of thick c-BN
films (> 1 µm) are described and commented. Experimental results from
authors laboratory are presented regarding the deposition and characterization
of c-BN based nanocomposites (c-BN/a-C) as well as metastable c-BN:O films. Also
illustrated is a specially designed growth scheme for realization of adherent,
2 µm thick, superhard c-BN:O films on silicon substrates. Its advantages as well as upscale
capability are discussed.