MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 81

0.6

CP Titanium

0.5

Ti-13Nb-13Zr

Ti-6Al-4V

0.4

Co-28Cr-6Mo

0.3

Ti-5Al-2.5Fe

0.2

0.1

0.0

0 2000 4000 6000

No. of cycles

8000 10000

Figure 3.13. Comparative plot, showing the evolution of coeffi cient of friction (COF) with
number of fretting cycles for potential orthopedic implant materials against steel at 10 N load,
10 Hz frequency, and 80

m displacement stroke 100 .

μ

and the Ni : Cr ratio in the tissues adjacent to stainless steel implants is greater in
infected cases than that in non-infected cases. Thus, infection as a cause of allergy
has to be considered.
As a result, using a different alloy (other than steel) for metal implants was
tested. Williams and Clark 103 compared the corrosion of cobalt in aqueous media
both with and without the presence of the protein serum albumin, using a number
of experimental techniques. The corrosion rate was found to increase signifi cantly
in the presence of albumin. Although the effect was related to albumin concentra-
tion to a certain extent, there was no equivalence between the metal ions released
and the albumin present. It was believed that the effect was due to a catalytic
process, where the albumin reversibly bound cobalt during the corrosion process.
Spriano et al. 104 characterized the samples of Ti-6Al-7Nb alloy with surfaces
presenting a different chemical and mechanical state. Their results show that the
Ti-6Al-7Nb alloy presents bioactive ability and good corrosion resistance after an
appropriate surface treatment, which consists of a two-step chemical etching and
heat treatment.
In evaluating the corrosion behavior of Ti based alloys in Hank's solution,
Choubey et al. 105 compared electrochemical and corrosion behavior results for
four different types of alloys: Ti - 6Al - 4V, Ti - 6Al - 4Nb, Ti - 6Al - 4Fe and Ti - 5Al -
2.5Fe. The passivation parameters of breakdown potential (E b ), passive current
density (i pass ), and the passive range (E b -ZCP) were estimated from the polariza-
tion curves; these are tabulated in Table 3.6.
The zero current potential (ZCP) of all Ti-alloys was in the range of

− 276 to

− 585 mV vs. SCE. The passive current densities were obtained around the middle

of the passive range (Table 3.6). The passive current densities of the alloys inves-