LASER PROCESSING OF ORTHOPEDIC BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 307

and 0.17 out to 80 m sliding distance for Ti-6Al-4V ELI and the TNZT + 2B,
respectively. These are very low friction coeffi cients typically exhibited for oxi-
dized titanium materials [45]. In addition, these friction coeffi cients show much
less fl uctuations compared to their as-synthesized state, suggesting a more stable
sliding interface without debris in the contact. The values are also consistent with
the corresponding wear track morphologies shown in Figures 9.25 and 9.26 .
Based on these SEM images, both wear track morphologies exhibit a change
in mechanism to mild oxidative wear, which suppresses the previous plastically
dominated wear mechanisms shown for the as-synthesized alloys. The toughened

(a)

200 μ m

(b)

30 μ m

Figure 9.25. (a) Lower magnifi cation and (b) higher magnifi cation secondary SEM images of
wear tracks on the surface of oxidized Ti-6Al-4V ELI after friction studies using Si 3 N 4 counter-
face balls. [Sonia Samuel et al. Wear Resistance of Laser Deposited Boride Reinforced Ti - Nb - Zr -
Ta Alloy Composites for Orthopedic Implants (to appear in Mater. Sci. Eng. C, 2007)]