230
Z. Wang et al.
the not change along the depth of the section. It can be seen that the microhardness
of the treated samples surface has improved to various degrees, and the maximum
microhardness of each group of samples is on the surface. Among them, the highest
value is 842.3 HV 0.3 at 1200 N, which is 12.8% higher than that of the untreated
sample. By comparing the surface microstructure of the samples at different static
loads (Fig. 18.6), it can be found that the value at 1200 N is higher than that of the other
group, since the surface of the sample can obtain a relatively finer microstructure,
the effect on the material refinement is the most significant at the this static load. At
1000 N static load, SURP has a slighter effect on the surface microstructure compared
with 1200 N, and the surface hardness is 831.4 HV 0.3 . When the static load is 800 and
600 N, although SURP has a certain refinement effect on the surface microstructure
of the samples, it is relatively limited. Compared with the 1200 N sample, the surface
microstructures of the above two groups of samples are coarser, the surface hardness
is 813.5 and 796.2 HV 0.3 , respectively. From the analysis above, it is can be known
that surface hardness of the material can be improved consistently by increasing the
static load in the range of 0–1200 N.
In addition, as the increase of static load within a certain range, the depth of
refined layer of the sample is also improved. The depth of the refined layer of the
600, 800 and 1000 N samples are 40, 80 and 100 μm, respectively. When the static
load increases to 1200 N, the depth of the refined layer is 100 μm, which is same
as the 1000 N sample. From the surface to 60 μm, the microhardness of the 1200 N
sample is higher than that of the 1000 N sample at the same depth; however when
the depth exceeds 60 μm, the two groups of samples share the same microhardness
at the same depth, so it cannot be proved that when the static load exceeds 1000 N,
the depth of the refined layer can be improved.
18.3.3 Surface Residual Compressive Stress
Figure 18.9 shows the residual compressive stress on the surface of the sample at
different static loads. The surface residual compressive stress of the untreated sample
is −191.3 MPa. As the static load increases, the value on the surface of the sample is
also improved. The value of the sample at static loads of 600, 800, 1000 and 1200 N
is −399.2, −493.6, −610.1 and −674.8 MPa, respectively. Among them, 1200 N
sample obtains the most significant growth of the residual compressive stress on the
surface. but there is no the marked gap of residual compressive stress between 1000 N
and 1200 N samples (only increased by −74.7 MPa). Although the nonuniform plastic
deformation in the treated area is improved during this process, a small number of
defects and micro-cracks appear on the surface of the 1200 N sample (Fig. 18.4d),
resulting in the release of a small amount of residual compressive stress [25].
In the SURP process, the nonuniform plastic deformation occurs on the surface of
the sample, which causes the lattice distortion of the surface microstructure, leading
to residual compressive stress, and the residual compressive stress on the surface of
the material can partially offset the stress on the working surface to improve the wear
Z. Wang et al.
the not change along the depth of the section. It can be seen that the microhardness
of the treated samples surface has improved to various degrees, and the maximum
microhardness of each group of samples is on the surface. Among them, the highest
value is 842.3 HV 0.3 at 1200 N, which is 12.8% higher than that of the untreated
sample. By comparing the surface microstructure of the samples at different static
loads (Fig. 18.6), it can be found that the value at 1200 N is higher than that of the other
group, since the surface of the sample can obtain a relatively finer microstructure,
the effect on the material refinement is the most significant at the this static load. At
1000 N static load, SURP has a slighter effect on the surface microstructure compared
with 1200 N, and the surface hardness is 831.4 HV 0.3 . When the static load is 800 and
600 N, although SURP has a certain refinement effect on the surface microstructure
of the samples, it is relatively limited. Compared with the 1200 N sample, the surface
microstructures of the above two groups of samples are coarser, the surface hardness
is 813.5 and 796.2 HV 0.3 , respectively. From the analysis above, it is can be known
that surface hardness of the material can be improved consistently by increasing the
static load in the range of 0–1200 N.
In addition, as the increase of static load within a certain range, the depth of
refined layer of the sample is also improved. The depth of the refined layer of the
600, 800 and 1000 N samples are 40, 80 and 100 μm, respectively. When the static
load increases to 1200 N, the depth of the refined layer is 100 μm, which is same
as the 1000 N sample. From the surface to 60 μm, the microhardness of the 1200 N
sample is higher than that of the 1000 N sample at the same depth; however when
the depth exceeds 60 μm, the two groups of samples share the same microhardness
at the same depth, so it cannot be proved that when the static load exceeds 1000 N,
the depth of the refined layer can be improved.
18.3.3 Surface Residual Compressive Stress
Figure 18.9 shows the residual compressive stress on the surface of the sample at
different static loads. The surface residual compressive stress of the untreated sample
is −191.3 MPa. As the static load increases, the value on the surface of the sample is
also improved. The value of the sample at static loads of 600, 800, 1000 and 1200 N
is −399.2, −493.6, −610.1 and −674.8 MPa, respectively. Among them, 1200 N
sample obtains the most significant growth of the residual compressive stress on the
surface. but there is no the marked gap of residual compressive stress between 1000 N
and 1200 N samples (only increased by −74.7 MPa). Although the nonuniform plastic
deformation in the treated area is improved during this process, a small number of
defects and micro-cracks appear on the surface of the 1200 N sample (Fig. 18.4d),
resulting in the release of a small amount of residual compressive stress [25].
In the SURP process, the nonuniform plastic deformation occurs on the surface of
the sample, which causes the lattice distortion of the surface microstructure, leading
to residual compressive stress, and the residual compressive stress on the surface of
the material can partially offset the stress on the working surface to improve the wear