Surface Nanostructuring of Metallic Materials …
477
The corrosion behavior of untreated and SMATed AISI 316L stainless steel in
0.1 M NaCl is evaluated by Hao et al. [32]. According to them, the formation of a
nanocrystalline surface (19 nm) has led to a decrease in corrosion resistance. The
increase in grain boundary density, structural inhomogeneity and transformation of
the austenite to α’-martensite phase are considered responsible for the decrease in
corrosion resistance. However, annealing of the SMATed 316L stainless steel at 300–
380 °C promotes the diffusion of Cr from the matrix to the surface, which facilitates
the formation of the passive film and improves the corrosion resistance.
Balusamy et al. [10, 29] have evaluated the corrosion resistance of untreated
AISI 304 stainless steel and those subjected to SMAT using 2, 5 and 8 mm Ø 316L
stainless steel balls for 15–60 min, in 0.6 M NaCl as well as in Ringer’s solution.
An improvement in corrosion resistance is observed only for 304 stainless steels
treated using 2 mm Ø balls. In contrast, SMAT using 5 and 8 mm Ø balls has led
to a decrease in corrosion resistance. Many factors could influence the corrosion
behavior of SMAT 304 stainless steels. Establishing a direct correlation between the
corrosion behavior of the treated 304 stainless steel and the factors influencing it is
quite complex. In most instances, the corrosion resistance is influenced by more than
one factor. All of these factors, either individually or in combination could influence
the corrosion resistance of the treated 304 stainless steel. The increase in surface
roughness, a transformation of the austenite to α’-martensite phase, higher extent of
deformation and presence of a larger number of defects/dislocations are responsible
for the observed decrease in corrosion resistance of 304 SS treated using 5 and 8 mm
Ø balls when compared to the untreated one in Ringer’s solution as well as 0.6 M
NaCl. The grain refinement, surface nanocrystallization, selective dissolution of Fe
and enrichment of Cr at the surface have increased the number of nucleation sites
and promotes the formation of an intact and highly protective passive oxide layer on
304 stainless steel treated using 2 mm Ø balls when compared to the untreated one,
in Ringer’s solution as well as 0.6 M NaCl. The defects induced during SMAT and
the increase is surface roughness should be limited which would otherwise cause a
deleterious influence on the corrosion resistance.
The corrosion behavior of untreated 301 stainless steel and those subjected to
SMAT using 2 mm Ø 304 stainless steel balls for 5 to 20 min, in 0.6 M NaCl
is evaluated by Olugbade et al. [33]. The formation of a nanostructured surface has
offered an improvement in the corrosion resistance for SMAT 301 stainless steel when
compared to its untreated counterpart. The shift in corrosion potential (E corr ) towards
more noble values, decrease in corrosion current density (i corr ), higher charge transfer
resistance (R ct ) and a higher phase angle validates the inference. The improvement
in corrosion resistance of SMAT 301 stainless steel is due to its ability to facilitate
diffusion of Cr to the surface, thus enabling the formation of a strong passive oxide
layer.
Mechanical failure of metallic biomaterials is often related to corrosion fatigue
phenomena. Pitting corrosion is often considered to be the active mechanism through
which fatigue cracks initiate. Microstructural aspects are closely related to the corrosion fatigue strength of biomedical alloys. The mechanism of corrosion fatigue of
biomedical metallic alloys and the ways of mitigation is reviewed by Antunes and de
477
The corrosion behavior of untreated and SMATed AISI 316L stainless steel in
0.1 M NaCl is evaluated by Hao et al. [32]. According to them, the formation of a
nanocrystalline surface (19 nm) has led to a decrease in corrosion resistance. The
increase in grain boundary density, structural inhomogeneity and transformation of
the austenite to α’-martensite phase are considered responsible for the decrease in
corrosion resistance. However, annealing of the SMATed 316L stainless steel at 300–
380 °C promotes the diffusion of Cr from the matrix to the surface, which facilitates
the formation of the passive film and improves the corrosion resistance.
Balusamy et al. [10, 29] have evaluated the corrosion resistance of untreated
AISI 304 stainless steel and those subjected to SMAT using 2, 5 and 8 mm Ø 316L
stainless steel balls for 15–60 min, in 0.6 M NaCl as well as in Ringer’s solution.
An improvement in corrosion resistance is observed only for 304 stainless steels
treated using 2 mm Ø balls. In contrast, SMAT using 5 and 8 mm Ø balls has led
to a decrease in corrosion resistance. Many factors could influence the corrosion
behavior of SMAT 304 stainless steels. Establishing a direct correlation between the
corrosion behavior of the treated 304 stainless steel and the factors influencing it is
quite complex. In most instances, the corrosion resistance is influenced by more than
one factor. All of these factors, either individually or in combination could influence
the corrosion resistance of the treated 304 stainless steel. The increase in surface
roughness, a transformation of the austenite to α’-martensite phase, higher extent of
deformation and presence of a larger number of defects/dislocations are responsible
for the observed decrease in corrosion resistance of 304 SS treated using 5 and 8 mm
Ø balls when compared to the untreated one in Ringer’s solution as well as 0.6 M
NaCl. The grain refinement, surface nanocrystallization, selective dissolution of Fe
and enrichment of Cr at the surface have increased the number of nucleation sites
and promotes the formation of an intact and highly protective passive oxide layer on
304 stainless steel treated using 2 mm Ø balls when compared to the untreated one,
in Ringer’s solution as well as 0.6 M NaCl. The defects induced during SMAT and
the increase is surface roughness should be limited which would otherwise cause a
deleterious influence on the corrosion resistance.
The corrosion behavior of untreated 301 stainless steel and those subjected to
SMAT using 2 mm Ø 304 stainless steel balls for 5 to 20 min, in 0.6 M NaCl
is evaluated by Olugbade et al. [33]. The formation of a nanostructured surface has
offered an improvement in the corrosion resistance for SMAT 301 stainless steel when
compared to its untreated counterpart. The shift in corrosion potential (E corr ) towards
more noble values, decrease in corrosion current density (i corr ), higher charge transfer
resistance (R ct ) and a higher phase angle validates the inference. The improvement
in corrosion resistance of SMAT 301 stainless steel is due to its ability to facilitate
diffusion of Cr to the surface, thus enabling the formation of a strong passive oxide
layer.
Mechanical failure of metallic biomaterials is often related to corrosion fatigue
phenomena. Pitting corrosion is often considered to be the active mechanism through
which fatigue cracks initiate. Microstructural aspects are closely related to the corrosion fatigue strength of biomedical alloys. The mechanism of corrosion fatigue of
biomedical metallic alloys and the ways of mitigation is reviewed by Antunes and de