Nano Si 3 N 4 composites with tailored microstructure were developed using fi ne ß-Si 3 N 4 powders. Their wear behaviour was investigated. Whereas pure Si 3 N 4 composites showed improved wear behaviour under dry rolling conditions with slip, TiN-reinforced nano Si 3 N 4 composites generate a self-lubricating behaviour under dry sliding conditions. After chemical treatment with hydrogen sulphide, the friction coeffi cient and wear rate was found to be signifi cantly decreased under dry sliding conditions. Additionally, the new composites possess higher fracture toughness than the pure nano Si 3 N 4 materials.

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The densification behaviors of two silicon nitride nanopowder mixtures based respectively on a-Si3N4 and ß-Si3N4 as the major phase constituent were studied by spark plasma sintering. Sintering conditions were established where a low viscous liquid not in equilibrium with the main crystalline constituent(s) stimulated the grain sliding yet did not activate the reprecipitation mechanism that unavoidably yields grain growth. By this way of dynamic grain sliding full densification of silicon nitride nanoceramics was achieved with no noticeable involvement of a- to ß-Si3N4 phase transformation and grain growth. This processing principle opens the way toward flexible and precise tailoring of the microstructures and properties of Si3N4 ceramics. The obtained silicon nitride nanoceramics showed improved wear resistance, particularly under higher Hertzian stresses

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