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 . 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.