Biomedical Engineering Reference
In-Depth Information
image of the modulated contrast is shown in Figure 9.10b. This modulated con-
trast occurs at a highly refi ned scale in this material (
50 nm as seen in Figure
9.10b). While the origin of this modulated contrast is the subject of ongoing inves-
tigations, based on its appearance it can be speculated that this contrast is arising
from a highly-refi ned dendritic solidifi cation of this alloy. Such refi ned scale den-
drites are likely in LENS™ deposited alloys due to the rapid solidifi cation rates
inherent to the process [3,24].
<
9.3.3.4 Corrosion Resistance of LENS™ Deposited Ti-Nb-Zr-Ta
Alloys.
Anodic polarization tests were carried out on LENS™ deposited TNZT,
CP Ti and Ti-6Al-4V ELI samples and also on the boride reinforced TNZT sam-
ples. The specimens used were in the form of discs with a diameter of 15 mm and
were polished to a surface fi nish of 0.3
m. The samples were then cleaned ultra-
sonically and were employed as the working electrode in the test cell. The tests
were carried out in two different media, 0.1 N HCl and a simulated body solution
known as the Ringers Solution. The Ringers solution has a composition of NaCl
9 g/l, KCl 0.43 g/l, CaCl
2
0.24 g/l, NaHCO
3
0.2 g/l [34] . The anodic polarization test
was performed from an initial potential of
μ
1.5 Volts to 5V at room temperature
at a scan rate of 0.166 mV/s and the current density was recorded continuously.
A saturated calomel electrode was used as a reference electrode and a platinum
wire as a counter electrode. The tests were repeated to ensure the reproducibility
of the data obtained. A detailed spectroscopic analysis using X-Ray photoelec-
tron spectroscopy was performed on the corrosion product (oxide layer) formed
on the TNZT alloy.
Anodic polarization plots for the three materials in 0.1 N HCL, LENS™
deposited TNZT, CP Ti and Ti-6Al-4V are shown in Figure 9.11. All the three
−
Polarization Curve-0.1 N HCI
6
CP Ti
Ti-6A1-4V
TNZT
5
4
3
2
1
0
-1
-2
0.00001
0.0001
0.001
0.01
0.1
1
10
100
Current Density A/m^2
Figure 9.11.
Anodic Polarization curve for CP-Ti, Ti-6Al-4V ELI and TNZT in 0.1 N HCl. [Sonia
Samuel, (M.S. Thesis, Dept of Mater. Sci. and Eng., University of North Texas, 2007)]
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