Surface Nanostructuring of Metallic Materials …
485
improvement in tribological behaviour of SMAT Ti. The fretting wear resistance of
SMAT Ti is also found to be much higher than untreated Ti [51].
The effect of SMAT on the corrosion behaviour of CP-Ti, Ti6Al4V and β-phase Ti
alloys in 3.5% NaCl and simulated body fluid (SBF) is studied by many researchers
[7, 16, 53, 54]. The corrosion resistance of untreated and SMAT CP-Ti in 3.5%
NaCl is evaluated by Fu et al. [16]. According to them, SPD induced during SMAT
increases the diffusion pathway and promotes permeation of a larger amount of
oxygen into the subsurface Ti. The higher oxygen content is expected to help in the
formation of an intact passive oxide layer. The grain refinement and an increase in
grain boundary density following the SPD induced by SMAT facilitate nucleation of
the passive oxide layer. The higher thickness of the stable passive oxide layer formed
on SMAT Ti is very effective in decreasing the permeation of the aggressive chloride
ions, which would otherwise cause pitting corrosion [16].
The corrosion resistance of untreated and SMAT Ti6Al4V alloy in Ringer’s solution (pH: 7.2, at 37 °C) is evaluated by Jelliti et al. [7]. The variation in open circuit
potential (OCP) of untreated and SMAT Ti6Al4V alloy in Ringer’s solution measured
as a function of time indicates that both of them are capable of forming an oxide
film, which is evident from the positive shift in OCP with time. However, when
compared to the oxide layer formed on the untreated alloy, the one formed on SMAT
Ti6Al4V appears to be effective. The anodic branch of the potentiodynamic polarization curve reveals passivation of both untreated and SMAT Ti6Al4V alloy with
no significant difference in the breakdown potentials between them. The E corr and
i corr of coarse-grained untreated Ti6Al4V alloy is −330 mV vs. SCE and 52 nA/cm
2 .
After SMAT using 2 mm and 3 mm Ø 100Cr6 balls for 15 and 20 min, respectively,
the E corr values exhibit a shift towards the noble direction to −275 mV vs. SCE and
−235 mV vs. SCE, respectively while the i corr values are decreased to 35 nA/cm
2
and 22 nA/cm
2 , respectively. However, EIS study clearly indicates the difference
in ability between them. The R ct of the coarse-grained untreated Ti6Al4V alloy is
10.56 k/cm
2 . However, after SMAT using 2 mm and 3 mm Ø 100Cr6 balls for 15
and 20 min, the R ct values increased to 763.41 and 1700 k/cm
2 , respectively. XPS
analysis of untreated and SMAT Ti6Al4V alloy reveals enrichment of oxygen for
the treated alloy, which supports easy amenability of the SMAT Ti6Al4V alloy to
form a stable passive oxide layer. XPS analysis performed on the passive oxide layer
formed on untreated and SMAT Ti6Al4V alloy after immersion in Ringer’s solution
for one weak indicate the presence of TiO 2 as the predominant species. Hence, it is
clear that SMAT is beneficial in improving the corrosion resistance of Ti6Al4V alloy
in Ringer’s solution.
The corrosion behavior of solution treated coarse-grained pure β phase Ti-25Nb3Mo-3Zr-2Sn alloy (TLM alloy), those subjected to SMAT using 2 mm Ø zirconia
balls at 50 Hz for 30 min and SMATed TLM alloy subjected to post-annealing at
200 °C for 10 h under vacuum (7.5 × 10
−4 Pa), in 0.9% NaCl and SBF, is evaluated
by Huang et al. [53]. The E corr and i corr of the solution treated TLM alloy are −
660 mV vs. SCE and 2.08 × 10
−6 A/cm
2 , respectively. SMAT has enabled a shift in
E corr towards noble direction from −660 mV vs. SCE to −410 mV vs. SCE and a onefold decrease in i corr from 2.08 × 10
−6 A/cm
2 to 1.28 × 10
−7 A/cm
2 . Post annealing
485
improvement in tribological behaviour of SMAT Ti. The fretting wear resistance of
SMAT Ti is also found to be much higher than untreated Ti [51].
The effect of SMAT on the corrosion behaviour of CP-Ti, Ti6Al4V and β-phase Ti
alloys in 3.5% NaCl and simulated body fluid (SBF) is studied by many researchers
[7, 16, 53, 54]. The corrosion resistance of untreated and SMAT CP-Ti in 3.5%
NaCl is evaluated by Fu et al. [16]. According to them, SPD induced during SMAT
increases the diffusion pathway and promotes permeation of a larger amount of
oxygen into the subsurface Ti. The higher oxygen content is expected to help in the
formation of an intact passive oxide layer. The grain refinement and an increase in
grain boundary density following the SPD induced by SMAT facilitate nucleation of
the passive oxide layer. The higher thickness of the stable passive oxide layer formed
on SMAT Ti is very effective in decreasing the permeation of the aggressive chloride
ions, which would otherwise cause pitting corrosion [16].
The corrosion resistance of untreated and SMAT Ti6Al4V alloy in Ringer’s solution (pH: 7.2, at 37 °C) is evaluated by Jelliti et al. [7]. The variation in open circuit
potential (OCP) of untreated and SMAT Ti6Al4V alloy in Ringer’s solution measured
as a function of time indicates that both of them are capable of forming an oxide
film, which is evident from the positive shift in OCP with time. However, when
compared to the oxide layer formed on the untreated alloy, the one formed on SMAT
Ti6Al4V appears to be effective. The anodic branch of the potentiodynamic polarization curve reveals passivation of both untreated and SMAT Ti6Al4V alloy with
no significant difference in the breakdown potentials between them. The E corr and
i corr of coarse-grained untreated Ti6Al4V alloy is −330 mV vs. SCE and 52 nA/cm
2 .
After SMAT using 2 mm and 3 mm Ø 100Cr6 balls for 15 and 20 min, respectively,
the E corr values exhibit a shift towards the noble direction to −275 mV vs. SCE and
−235 mV vs. SCE, respectively while the i corr values are decreased to 35 nA/cm
2
and 22 nA/cm
2 , respectively. However, EIS study clearly indicates the difference
in ability between them. The R ct of the coarse-grained untreated Ti6Al4V alloy is
10.56 k/cm
2 . However, after SMAT using 2 mm and 3 mm Ø 100Cr6 balls for 15
and 20 min, the R ct values increased to 763.41 and 1700 k/cm
2 , respectively. XPS
analysis of untreated and SMAT Ti6Al4V alloy reveals enrichment of oxygen for
the treated alloy, which supports easy amenability of the SMAT Ti6Al4V alloy to
form a stable passive oxide layer. XPS analysis performed on the passive oxide layer
formed on untreated and SMAT Ti6Al4V alloy after immersion in Ringer’s solution
for one weak indicate the presence of TiO 2 as the predominant species. Hence, it is
clear that SMAT is beneficial in improving the corrosion resistance of Ti6Al4V alloy
in Ringer’s solution.
The corrosion behavior of solution treated coarse-grained pure β phase Ti-25Nb3Mo-3Zr-2Sn alloy (TLM alloy), those subjected to SMAT using 2 mm Ø zirconia
balls at 50 Hz for 30 min and SMATed TLM alloy subjected to post-annealing at
200 °C for 10 h under vacuum (7.5 × 10
−4 Pa), in 0.9% NaCl and SBF, is evaluated
by Huang et al. [53]. The E corr and i corr of the solution treated TLM alloy are −
660 mV vs. SCE and 2.08 × 10
−6 A/cm
2 , respectively. SMAT has enabled a shift in
E corr towards noble direction from −660 mV vs. SCE to −410 mV vs. SCE and a onefold decrease in i corr from 2.08 × 10
−6 A/cm
2 to 1.28 × 10
−7 A/cm
2 . Post annealing