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Tribological properties
of ceramics such as Si3N4,
SiC, Al2O3 and ZrO2
were investigated in various environments, and surface
modification by metallic coatings was made to these
ceramics in order to improve the wear resistance
at high temperatures. The results obtained are summarized
as follows.
The frictional coefficients
of these ceramics at high temperatures up to 1,000℃
were found to be within a range of 0.5 to 1.1, while
the sliding pair of SiC/SiC showed a low friction
at the beginning of the test. The wear rate of these
ceramics except Al2O3 increased
to an order of 10|3mm/(N¥m) with increasing
atmospheric temperature to 1,000℃.
In aqueous H2SO4
solution, the wear rate of Si3N4
showed the maximum at a concentration around 20
wt“ of H2SO4, resulting from
the grain boundary corrosion. In distilled water,
very low friction corresponding to a coefficient
of 0.01 was realized with SiC and Si3N4
after "running-in", i.e., forming a very smooth
surface. Similar results were also obtained in organic
solutions with functional group such as alcohol
and caprylic acid. Appropriate metallic film coatings
for individual ceramics were found to remarkably
reduce the wear rates at higher temperatures.
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