Development of sialon ceramics for lubricated sliding applications

Microstructural design and characterization of mechanical as well as
tribological. properties of sialon ceramics are the aim of this work. A
potential application for these materials are fuel injection pumps for
gasoline engines. The currently used metal parts face severe
tribological damage with increasing pumping pressures and thus a
replacement is needed. Sialon ceramics offer a wide variety of
compositional parameters which allow to tailor microstructure and
mechanical properties in order to meet the tribological requirements.
Since phase boundaries in the sialon system shift depending on the
additive elements used, investigations of the phase relations have been
performed for two different sintering additives in order to gain
informations about reasonable starting compositions. Then, the ratio of
the sialon modifications, the amount of grain boundary phase and the
grain morphologies have been correlated with the initial composition
and the amount of sintering additives. For high hardness values an
increase of the fraction of the alpha-sialon modification in mixed
alpha/beta-sialon materials is beneficial. The fracture toughness can
... mehr
be raised by promoting growth of elongated grains. It can be done
either by achieving higher beta-sialon fractions in mixed
alpha/beta-sialon ceramics or by sintering with an excess of additive
in pure alpha-sialon materials. Under lubricated sliding with
isooctane, sialon ceramics showed a more advantageous behaviour with
regard to friction coefficients and wear than commercial silicon
nitride and coarse-grained alumina.