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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 α‐sialon modification in mixed α/β‐sialon materials is beneficial. The fracture toughness can be raised by promoting growth of elongated grains. It can be done either by achieving higher β‐sialon fractions in mixed α/β‐sialon ceramics or by sintering with an excess of additive in pure α‐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.