The following NanoTest results were obtained from a hydroxylapatite coating deposited on a titanium alloy. After an initial topography determination, 14 sequential friction measurements were carried out, with a topography measurement being performed between each one. For each scratch, a constant load of 75 mN was applied abruptly at the same point along the path of the stylus. A 120° conical diamond probe was used, with a tip radius of 25 µm.

For the scratched area, the three figures show: (1) the actual topography evolution with continued scratching; (2) a progressive increase in plastic depth with sequential scratching; and (3) the occurrence of a maximum frictional force during the scratching sequence.

The first two figures show a significant change in average wear rate with an increasing number of scratches. Essentially, this increased significantly after the first few passes, with the maximum rate corresponding to the maximum frictional force. The results are indicative of different wear mechanisms, such as initial film cohesion failure followed by adhesion failure.