Use of lubricious, high-temperature-capable ceramic-piston-rings may r
educe frictional losses in engines. Silicon nitride (Si3N4) rings with
a functional gradient of titanium nitride (TiN) towards the ring outs
ide diameter (OD) were fabricated by centrifugal spinning of a ceramic
slurry followed by nitriding. A 10 volume percent (v/o) TiN-silicon s
lurry resulted in a greater concentration of TiN (and higher microhard
ness) near the ring OD (compared to 20 v/o TiN). Unlubricated pin-on-d
isk tests of a 10 v/o TiN/Si3N4 pin vs. a 30 v/o TiC/Si3N4 disk in air
exhibited coefficients of friction (COF) of about 0.65 that were inde
pendent of temperature (20-800 degrees C). Wear tests were also perfor
med in which boron nitride (BN) powder was added between the ceramic p
in and ceramic disk materials, which subsequently reduced COF to <0.2
for temperatures less than or equal to 300 degrees C.