TITANIUM NITRIDE AND DIAMOND LIKE CARBON COATINGS FOR CARDIOVASCULAR APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 680

Figure 21.4. Wear surface topography of UHMWPE (initial surface fi nish 0.15 μ m Ra typical)
against bare metal and coated counter faces: (a) Wear contour plot (b) Wear tracks generated
by Ti6Al4V pin (c) Wear track generated by TiN coated Ti6Al4V pin (d) Wear track generated
by DLC-coated Ti pin. The average surface roughness of wear tracks are less when the pin is
coated. Titanium nitride counter face generates the smoothest wear tracks and hence could
result in minimum wear debris formation. (See color insert.)
21.7.4 Coating Adhesion Studies
The coating adhesion studies were carried out using a micro scratch test system
(Micro—Combi Tester, M/s. CSM Instruments, USA). Scratch testing is a compre-
hensive method of quantifying the adhesion properties of coatings. The technique
involves generating a controlled scratch with a diamond tip on the sample under
test. The tip, either a Rockwell C diamond or a sharp metal tip, is drawn across the
coated surface under either a constant or progressive load. At a certain critical
load, the coating will start to fail. The critical loads are used to quantify the adhe-
sive properties of different fi lm-substrate combinations. These parameters consti-
tute a unique signature of the coating system under test.
The test conditions are chosen to ensure that reproducible scratch maps are
obtained for the coating under investigation [see Table 21.6]. The critical loads are