84
A. Meher and M. M. Mahapatra
respectively. For the magnesium alloy (RZ5), for an initial sliding distance of 1000 m
the wear loss was 306.87 mg, whereas for the next 1000 m sliding distance the wear
loss was 152.30 mg, followed by 109.33 mg for another 1000 m. This indicates
that due to continuous sliding of the chosen materials for a longer distance, the rate
of wear gradually decreases. This is because of the formation and presence of a
protective oxide layer due to frictional heating. As the test sample slides over the
abrasive surface, the material wears out and generates wear debris. Gradually, the
debris gets deposited in the wear groove and forms oxide debris due to frictional
heating. A continuous deposition of debris on the contact surface forms a protective
oxide layer, which acts as a resistance against wear [31, 32]. For the magnesium alloy
composite [RZ5/10 wt.% TiB 2 ], the rate of wear gradually decreases with an increase
in the sliding distance and this may be due to the similar effect of the formation of an
oxide layer. The wear loss behavior shows a similar trend for an applied load of 20 N
and 30 N as shown in Fig. 4c, e, respectively. It is also observed that due to frictional
heating the occurrence of thermal softening of the base magnesium alloy, which
tends to decrease the reinforcement-matrix interfacial bonding. Due to friction with
the abrasive surface the ceramic particles tend to be removed. However, the presence
of ceramic particulates does contribute to inhibiting the thermal softening of the
materials [33].
For a specific applied load condition, coefficient of friction (COF) increases with
increase in sliding distance as indicated in Fig. 4b, d, f. The coefficient of friction
values lies in the range of 0.470–0.573 for the magnesium alloy (RZ5) for the different
applied loads and for sliding distances of 1000, 2000 and 3000 m. Whereas, for the
magnesium alloy composite [RZ5/10 wt.% TiB 2 ] the coefficient of friction values lie
between 0.391 and 0.439. While comparing the three graphs, it is also observed that
the coefficient of friction of the materials decreases with an increase in applied load
for a particular sliding distance. Aatthisugan and co-workers noticed that coefficient
of friction increases with an increase in sliding distance for both the magnesium
alloy (AZ91D), the magnesium alloy composite [AZ91D/B 4 C] and the magnesium
alloy graphite hybrid composites [AZ91D/B 4 C-Graphite] for the different loading
conditions [23].
Surface Morphology and Microstructure of the Wear Surface
Wear occurs due to friction between the test sample and the counterface materials
with or without the presence of abrasive particles. Due to friction, plastic deformation
of material at the surface occurs and a thin layer of the material tends to delaminate
from the contact surface and releases itself in the form of chips [34]. The chips
generated due to delamination are either in the form of flakes or equiaxed debris. The
delamination of materials forms wear grooves on the contact surface and as the rate of
delamination gradually increases the depth and width of the grooves also increases.
Figure 5a, b The delamination of the magnesium alloy composite [RZ5/10 wt.%
TiB 2 ] at the different loading conditions is evident from the field emission scanning
A. Meher and M. M. Mahapatra
respectively. For the magnesium alloy (RZ5), for an initial sliding distance of 1000 m
the wear loss was 306.87 mg, whereas for the next 1000 m sliding distance the wear
loss was 152.30 mg, followed by 109.33 mg for another 1000 m. This indicates
that due to continuous sliding of the chosen materials for a longer distance, the rate
of wear gradually decreases. This is because of the formation and presence of a
protective oxide layer due to frictional heating. As the test sample slides over the
abrasive surface, the material wears out and generates wear debris. Gradually, the
debris gets deposited in the wear groove and forms oxide debris due to frictional
heating. A continuous deposition of debris on the contact surface forms a protective
oxide layer, which acts as a resistance against wear [31, 32]. For the magnesium alloy
composite [RZ5/10 wt.% TiB 2 ], the rate of wear gradually decreases with an increase
in the sliding distance and this may be due to the similar effect of the formation of an
oxide layer. The wear loss behavior shows a similar trend for an applied load of 20 N
and 30 N as shown in Fig. 4c, e, respectively. It is also observed that due to frictional
heating the occurrence of thermal softening of the base magnesium alloy, which
tends to decrease the reinforcement-matrix interfacial bonding. Due to friction with
the abrasive surface the ceramic particles tend to be removed. However, the presence
of ceramic particulates does contribute to inhibiting the thermal softening of the
materials [33].
For a specific applied load condition, coefficient of friction (COF) increases with
increase in sliding distance as indicated in Fig. 4b, d, f. The coefficient of friction
values lies in the range of 0.470–0.573 for the magnesium alloy (RZ5) for the different
applied loads and for sliding distances of 1000, 2000 and 3000 m. Whereas, for the
magnesium alloy composite [RZ5/10 wt.% TiB 2 ] the coefficient of friction values lie
between 0.391 and 0.439. While comparing the three graphs, it is also observed that
the coefficient of friction of the materials decreases with an increase in applied load
for a particular sliding distance. Aatthisugan and co-workers noticed that coefficient
of friction increases with an increase in sliding distance for both the magnesium
alloy (AZ91D), the magnesium alloy composite [AZ91D/B 4 C] and the magnesium
alloy graphite hybrid composites [AZ91D/B 4 C-Graphite] for the different loading
conditions [23].
Surface Morphology and Microstructure of the Wear Surface
Wear occurs due to friction between the test sample and the counterface materials
with or without the presence of abrasive particles. Due to friction, plastic deformation
of material at the surface occurs and a thin layer of the material tends to delaminate
from the contact surface and releases itself in the form of chips [34]. The chips
generated due to delamination are either in the form of flakes or equiaxed debris. The
delamination of materials forms wear grooves on the contact surface and as the rate of
delamination gradually increases the depth and width of the grooves also increases.
Figure 5a, b The delamination of the magnesium alloy composite [RZ5/10 wt.%
TiB 2 ] at the different loading conditions is evident from the field emission scanning