484
T. Balusamy et al.
and UTS (29.1%) of Ti after SMAT. The elongation to failure of untreated coarsegrained Ti is 21.7% whereas it improves to 39.1% for SMAT Ti. The mechanical
properties of coarse-grained untreated Ti6Al4V alloy and those subjected to SMAT
using 5 mm Ø SAE 52100 steel balls at 50 Hz for 30 and 60 min are studied by
Anand Kumar et al. [45]. According to them, only a slight increase in the YS (from
1063 to 1070 MPa) and UTS (from 1142 to 1173 MPa) of the Ti6Al4V alloy could
be observed after 30 min treatment. In contrast, an increase in treatment time from 30
to 60 min facilitated a good increase in YS (from 1063 to 1143 MPa) and UTS (from
1142 to 1268 MPa) of the Ti6Al4V alloy due to the higher level of work hardening
at the surface and near the surface. The formation of a nanocrystalline layer and high
dislocation densities induced by strain hardening during SMAT is considered as the
major factors responsible for the observed improvement in mechanical properties of
Ti and Ti6Al4V alloy after SMAT.
Anand Kumar et al. [45] have evaluated the fatigue life of untreated Ti6Al4V
alloy and those subjected to SMAT using 5 mm Ø SAE 52100 steel balls at 50 Hz
for 30 and 60 min. When compared to the coarse-grained untreated Ti6Al4V alloy,
the fatigue life of the alloy treated for 30 min is significantly improved. The fatigue
life is influenced by surface roughness, compressive residual stress, nanostructured
surface layer and work hardening. Higher surface roughness, which is commonly
observed for samples treated by SMAT, is likely to exert a deleterious influence on
fatigue life. In contrast, the compressive residual stress, formation of a nanostructured
surface layer and work hardening would exert a beneficial influence on the fatigue
life. Hence, the increase in fatigue life of Ti6Al4V alloy after SMAT for 30 min is due
to the beneficial effect of compressive residual stress, work hardening and surface
nanostructuring that could outweigh the negative effect of higher surface roughness.
The inferior fatigue life of the Ti6Al4V alloy after SMAT for 60 min is due to
the severe surface damage, resulting in the generation of numerous microcracks,
which are much deeper. The low ductility of the Ti6Al4V alloy is considered to be
responsible for the severe surface damage when the treatment time is increased from
30 to 60 min. The severe surface damage could have served as potential stress raisers
and aided a quicker initiation of a fatigue crack.
The tribological behavior of coarse-grained untreated Ti and those subjected to
SMAT using 8 mm Ø stainless steel balls at 50 Hz for 60 min under different loads
and dry sliding conditions was studied by Zhao et al. [44]. When mated against a
6 mm Ø AISI 52100 steel ball (HRC: 60), SMAT Ti displayed a low coefficient of
friction and wear volume. The improvement in wear resistance of SMAT Ti is due to
the grain refinement and higher hardness induced by SMAT. The wear mechanism
of SMAT Ti is governed by abrasive wear under 1 and 5 N, and a combination of
both abrasive and adhesive wear under 2 N. In contrast, the wear mechanism of
coarse-grained untreated Ti is governed by both abrasive and adhesive wear at 1 to
2 N while abrasive wear predominates at 5 N. Alikhani Chamgordanis et al. [15]
have also studied the tribological behavior of Ti before and after SMAT. According
to them, SMAT has decreased the coefficient of friction of Ti by 66%. The wear
rate of Ti is also decreased by about 60%. The refinement in grain size from 70 μm
to ~12 nm and a 2.8 times increase in hardness is considered responsible for the
T. Balusamy et al.
and UTS (29.1%) of Ti after SMAT. The elongation to failure of untreated coarsegrained Ti is 21.7% whereas it improves to 39.1% for SMAT Ti. The mechanical
properties of coarse-grained untreated Ti6Al4V alloy and those subjected to SMAT
using 5 mm Ø SAE 52100 steel balls at 50 Hz for 30 and 60 min are studied by
Anand Kumar et al. [45]. According to them, only a slight increase in the YS (from
1063 to 1070 MPa) and UTS (from 1142 to 1173 MPa) of the Ti6Al4V alloy could
be observed after 30 min treatment. In contrast, an increase in treatment time from 30
to 60 min facilitated a good increase in YS (from 1063 to 1143 MPa) and UTS (from
1142 to 1268 MPa) of the Ti6Al4V alloy due to the higher level of work hardening
at the surface and near the surface. The formation of a nanocrystalline layer and high
dislocation densities induced by strain hardening during SMAT is considered as the
major factors responsible for the observed improvement in mechanical properties of
Ti and Ti6Al4V alloy after SMAT.
Anand Kumar et al. [45] have evaluated the fatigue life of untreated Ti6Al4V
alloy and those subjected to SMAT using 5 mm Ø SAE 52100 steel balls at 50 Hz
for 30 and 60 min. When compared to the coarse-grained untreated Ti6Al4V alloy,
the fatigue life of the alloy treated for 30 min is significantly improved. The fatigue
life is influenced by surface roughness, compressive residual stress, nanostructured
surface layer and work hardening. Higher surface roughness, which is commonly
observed for samples treated by SMAT, is likely to exert a deleterious influence on
fatigue life. In contrast, the compressive residual stress, formation of a nanostructured
surface layer and work hardening would exert a beneficial influence on the fatigue
life. Hence, the increase in fatigue life of Ti6Al4V alloy after SMAT for 30 min is due
to the beneficial effect of compressive residual stress, work hardening and surface
nanostructuring that could outweigh the negative effect of higher surface roughness.
The inferior fatigue life of the Ti6Al4V alloy after SMAT for 60 min is due to
the severe surface damage, resulting in the generation of numerous microcracks,
which are much deeper. The low ductility of the Ti6Al4V alloy is considered to be
responsible for the severe surface damage when the treatment time is increased from
30 to 60 min. The severe surface damage could have served as potential stress raisers
and aided a quicker initiation of a fatigue crack.
The tribological behavior of coarse-grained untreated Ti and those subjected to
SMAT using 8 mm Ø stainless steel balls at 50 Hz for 60 min under different loads
and dry sliding conditions was studied by Zhao et al. [44]. When mated against a
6 mm Ø AISI 52100 steel ball (HRC: 60), SMAT Ti displayed a low coefficient of
friction and wear volume. The improvement in wear resistance of SMAT Ti is due to
the grain refinement and higher hardness induced by SMAT. The wear mechanism
of SMAT Ti is governed by abrasive wear under 1 and 5 N, and a combination of
both abrasive and adhesive wear under 2 N. In contrast, the wear mechanism of
coarse-grained untreated Ti is governed by both abrasive and adhesive wear at 1 to
2 N while abrasive wear predominates at 5 N. Alikhani Chamgordanis et al. [15]
have also studied the tribological behavior of Ti before and after SMAT. According
to them, SMAT has decreased the coefficient of friction of Ti by 66%. The wear
rate of Ti is also decreased by about 60%. The refinement in grain size from 70 μm
to ~12 nm and a 2.8 times increase in hardness is considered responsible for the