Biomedical Engineering Reference
In-Depth Information
Figure 5.23
Potentiodynamic corrosion curves for lat Ti-45S5 (a) and
porous Ti-45S5 (b) nanocomposites, etched in 1M H
3
PO
4
+
2% HF at 10 V for 30 min [16].
Another example of the porous nanomaterial is Ti-6Al-4V
alloy prepared by mechanical alloying and powder metallurgical
processes [15]. Jakubowicz and Adamek investigated corrosion
resistance of the nanocrystalline Ti-6Al-4V alloy before and after
anodic oxidation [15]. They compared the results to microcrystalline
counterpart. The corrosion resistance was investigated in simulated
body luids using potentiodynamic method (Fig. 5.24, Table 5.6). The
results are surprising, because the authors expected improvement
of the corrosion resistance due to the anodic oxidation, as was in the
case of pure porous Ti [14]. The polarization curves clearly shows,
that the lowest corrosion current has microcrystalline bulk alloy
(curve a). Etching of this sample results in increasing the corrosion
current (curve b). Corrosion resistance of the nanocrystalline
alloy (curve c) is signiicantly lower than the microcrystalline bulk
counterpart. After nanoparticles sintering, the sample has large
volume of the grain boundaries and density of about 90% of the
theoretical value, which means that the alloy has some pores inside,
which is normal after sintering. This structure and larger volume
of the grain boundaries are responsible for the total current low
during the corrosion test, different than for the bulk microcrystalline
sample. After additional electrochemical treatment, the sample is
etched through the grain boundaries, and anodic pores formation
take place. The density decreases to 80% of the theoretical value,
