Cubic Boron Nitride Based Metastable Coatings
and Nanocomposites
J. Ye, S. Ulrich, M. Stüber, C. Ziebert,
The 36th International Conference on Metallurgical
Coatings and Thin Films,
Carbon and Nitride Materials: Synthesis-Structure-Property Relationships
Boron Nitride and Carbon Nitride and Group-III (
Various PVD and plasma-assisted CVD methods presently used for the deposition
of cubic boron nitride (c-BN) thin films demand adequate conditions relating to
ion bombardment of growing films, growth temperature, film stoichiometry
etc. The ion-bombardment conditions, often appearing rather apparatus-specific,
can be however well categorized according to the fundamental parameters of
bombarding ions as well as condensing neutral particles, namely their energy
and flux density. In terms of these fundamental parameters, the mechanisms for
the c-BN formation are briefly discussed, along with an evaluation of the
available growth models. Due to intensive ion bombardment during deposition,
c-BN films are known for their extremely high compressive stress and poor
adhesion. The present study focuses then on the magnetron-sputtered, c-BN-based
metastable films and nanocomposite
films. Under suitable and wellcontrolled growth
parameters, the deposited films exhibit microstructures dominated by c-BN
phase, while on the other side show considerably reduced internal stresses in
comparison to conventional c-BN films. Some examples will be shown,
particularly c-BN/a-C nanocomposite and c-BN:O metastable films, including
their deposition details, structure and composition characterization (HRTEM,
SEM, XRD, XPS, AES, FTIR, etc.), and corresponding mechanical properties
(hardness, E-modulus, stress). A film design concept will also be demonstrated
as well as its successful realization for well-adherent films consisting of an
adhesion promoting base layer, a graded cubic-phase nucleation, and a low-stress,
superhard, above 2 μm
thick, c-BN-dominated top-layer.