was used. Testing velocity and sliding distance were set to 1 m/s
and 600 m, respectively. Each test was repeated three times.
During the abrasion tests, the effective power consumption was
measured by means of a high-resolution power module installed
in the test rig. With this data, the friction power PF [W] was
obtained by subtracting the idle power from the effective power
signal. The friction energy EF [J] was then calculated using the
friction power and the testing time tt as follows:
E Pt F = F t ( ) 1
The specific wear energy Ew [J/mm3
] was finally obtained from
the ratio of the friction energy to the volumetric loss VW of the
worn test specimens
E EV w FW = / ( ) 2
The influence of static oxidation on the wear rates obtained
from elevated temperature experiments was accounted for by
conducting a series of tests in which the specimens were heated
up to the desired temperature for the same duration (10 min) as
the abrasion tests but without any relative movement. The
objective of these tests was to quantify the weight gain due to
oxidation that occurs and to compensate the mass loss data using
these values. The oxidation was quantified by weighing the samples
before and after the static oxidation tests and the measured
value was subtracted from the mass loss values. The weight gain of
the materials due to oxidation is given in Table 3.
The mass loss was measured gravimetrically and volume loss
was calculated using the density of the materials. Finally, the
specific wear rate (SWR) of the specimens was calculated using
SWR / = VF S N ( ) 3
where V is the volume worn away in mm3
, FN is the normal load in
N and S is the sliding distance in m. The presence of embedded
abrasive particles on the surface of the samples was also taken into
account for the mass loss calculations. The mass of the embedded
particles (mEP) [7] was estimated using the following equation:
m A hc EP WT = ρA L ( ) 4
AWT is the wear track area. The density of the abrasive particles
(SiO2) ρA was taken as 2650 kg/m3
. The thickness of the layers (hL)
was considered as the average of 5 measurements at different
positions throughout the cross section of the wear track. The
quantitative analysis of the surface covered by abrasive particles
(c) was obtained using a Nikon Eclipse MA 200 optical microscope.
A series of 3 images for each testing parameter were randomly
taken from the worn surfaces of the specimens in a way that the
silica particles were easily distinguished from the metallic surface
(see Fig. 3(a)). The software NIS Elements was used to post-process
the obtained images. For each image, the observed phases were
manually determined to be silica particles or metallic material.
Colours were assigned to the phases i.e. blue to the silica particles
and grey to the metallic material (Fig. 3(b)). The pixels of each
phase were classified and counted. Finally the fraction area covered
by each phase was calculated.