Coating of Ti-6Al-4V alloy substrates with TiN/Ti multi-layered
films by magnetron sputtering in Ar gas atmosphere was examined, aiming at
the application of the alloy to artificial heart valves, in order to improve
not only the adhesion between the deposited film and the alloy but also the
surface smoothness of titanium nitride coatings and thereby to improve the
blood compatibility as well as the biocompatibility of the alloy coated with
the titanium nitride film. The effects of the thickness of the TiN (titanium
nitride) layer on the surface morphology of the film were investigated, in
order to develop TiN coatings with higher blood compatibility. The
multi-layered films were deposited by sputtering in sequence pure titanium
and titanium nitride targets. The thickness of titanium nitride layer was
varied from 300 nm to 800 nm, while that of pure titanium was constantly
200 nm. Under visual observation, the obtained multi-layered films looked
yellow gold and appeared to be uniform and adhesive, while TiN monolithic
films deposited directly onto the alloy substrate under the same sputtering
conditions peeled off partly. Therefore it was found that the multi-layered
thin films were more adhesive to the alloy than the monolithic films.
According to AFM (Atomic Force Microscope) images for both of the films, the
surface morphology of each TiN layer observed under the scope of
nanometer-scaled area was rough with pits and bumps, while that under the
scope of micrometer-scaled area was smooth without such pits and bumps.
Furthermore based on the AFM, the surface roughness $\sigma_{\it RMS}$
measured under the area of nanometer scale was found to increase with the
increase of the thickness of the TiN layer in the multi-layered film,
although that measured under the area of micrometer scale was assumed to be
independent of the thickness of the TiN layer.