Biomedical Engineering Reference
In-Depth Information
times lower (170 ± 10 HV0.2). It can be concluded that strength-
ening is due to nitrogen absorption process. Strengthening due to
HA addition need more detailed studies.
Table 6.5 summarizes also results of corrosion tests in Ringer's
solution performed at temperature 37
o
C. In Ringer's solution tests,
the corrosion current,
I
corr
, in the case of starting composition:
Fe
54
Cr
24
Mn
21
Mo
1
N is 6.9 × 10
-6
A/cm
2
and is associated with the
corrosion potential of -263 mV. The comparison of the values
E
corr
and
I
corr
indicates that addition of HA resulted in the shift of
the corrosion potential to a more negative value and appreciable
decrease in the corrosion current density. When the addition of
5% of HA results in small decrease of the corrosion current to
2.8 × 10
-6
A/cm
2
, the corresponding value in case of 10% addition
of HA is appreciable lower — one order of magnitude. Measured
values are considerably improved compared to widely used in
medicine 316L microcrystalline stainless steel. Comparison of the
corrosion current of the same sample (Fe
54
Cr
24
Mn
21
Mo
1
+ 5% HA)
before and after nitrogen absorption treatment emphasizes the
inluence of this process on the corrosion resistance — the difference
is two orders of magnitude. The polarization resistance values,
R
p
, calculated from the potentiodynamic curve were 14385 and
28143 Ohm/cm
2
for nanocomposites with 5% and 10% of HA,
respectively, which compared to 3747 Ohm/cm
2
for nickel-free
austenitic stainless steel also indicates huge impact of HA on
corrosion resistance of obtained nanocomposites. Calculated
corrosion rates for Fe
54
Cr
24
Mn
21
Mo
1
N/HA composites show
that corrosion rate is two (Fe
54
Cr
24
Mn
21
Mo
1
N + 5% HA) to eight
(Fe
54
Cr
24
Mn
21
Mo
1
N + 10% HA) times lower than in alloy without
HA content. Composite without nitrogen content (Fe
54
Cr
24
Mn
21
Mo
1
+ 5% HA) even with the addition of 5% HA shows unacceptable
corrosion rate of 1.420 mm/year, which conirms necessity of
nitrogen absorption treatment. From further research point of view,
Fe
54
Cr
24
Mn
21
Mo
1
N + 10% HA composite have the most promising
results of corrosion resistance (lowest corrosion rate combined
with lowest corrosion current).
Both nitrogen absorption treatment and the presence of HA
contribute to the higher corrosion resistance in Ringer's solution.
While pure nickel-free stainless steel with nanostructure has
signiicantly better corrosion properties and microhardness
compared to conventional 316L stainless steel, introduction of
