Deposition of cBN films was carried out in a R.F. diode sputtering apparatu
s with an auxiliary magnetic field using a boron carbide (B4C) target. Adhe
sion of the cBN films was vastly improved by a compositional gradient layer
which contains B, C and N. By employing this interlayer, the deposition of
thick (up to similar to 2 mum) and stable cBN films were enabled. The SIMS
depth profile measurements revealed that the gradient layer system started
with a boron carbide layer, which is the first layer on the substrate, and
had a composition approximately that of B,C. At the interface between the
B,C and the cBN layer, a step-like or continuous increase of N was clearly
visible while B and C decreased, respectively. From the IR spectra of each
gradient layer step, the B-C bonding was observed for the B,C layer and was
gradually replaced by sp(2) B-N as the N concentration was increased. The
gradient layer system exhibited relatively high plastic hardnesses ranging
from 24 to 30 GPa. The IR spectra of thick firms showed that these films co
ntain a high amount of cBN phase. The X-ray diffraction confirmed that the
film was predominately cBN and was [110] textured. The hardness measurement
s carried out by nano-indentation showed that these cBN layers have a hardn
ess of up to 60 GPa. The surface morphology was observed by AFM and the sur
face roughness increased with increasing coating thickness. Based on the re
sults of structural and mechanical property analysis, a primary mechanism f
or adhesion improvement will be proposed. (C) 2000 Elsevier Science B.V. Al
l rights reserved.