Using a hot filament chemical vapour deposition reactor, diamond films
of approximately 2-3 mum in thickness were deposited on tool steel
specimens with three different interlayer systems, namely CrN, Si and
borided steel. The morphology, defect densities and residual stresses
of the diamond films were strongly governed by the type of interlayer
used. Electrochemical potentiodynamic polarisation studies have been
carried out on the diamond deposited tool steel specimens in NaCl
solutions of two different concentrations, 0.01 M and 0.50 M,
respectively. The type of interlayer used for diamond coating on tool
steel has a strong influence on the corrosion potential. The maximum
shift in the equilibrium corrosion potential is observed for the
silicon interlayer. However, it leads to selective dissolution of the
carbide phase upon anodic polarisation. A near total resistance to
pitting of the CrN coated tool steel specimens is observed with the
introduction of a very thin diamond layer of 2 - 3 mum. With increasing
chloride ion concentration in the electrolyte, reverse trends in the
shift of EO, are observed for the blank tool steels in comparison to
the diamond-coated specimens. Detailed SEM characterisation of the
corrosion-tested specimens indicates the possible operating
mechanisms.