Si3N4/SiC MATERIALS BASED ON PRECERAMIC POLYMERS AND CERAMIC POWDER

A new way to manufacture Si3N4 ceramics is the combination of preceramic polymers with ceramic powder. Polycarbosilazane precursors can be used as an alternative binder which offers a high chemical purity, a homogeneous element distribution, flexible processing methods and a high ceramic yield. First, the Si3N4 powder is coated with the preceramic polymer and uniaxial pressed. Subsequent heat treatment converts the preceramic precursor into an amorphous SiCN ceramic. This new manufacturing process offers two unique possibilities: In contrast to the conventional fabrication processes for Si3N4, the precursor-powder-derived components exhibit a good mechanical stability even after pyrolysis at comparable low temperatures between 1000 and 1200 degrees C, when the ceramization of the precursor is completed. Thus, processing of various cost-efficient components are possible, if the thermal stability is more important for the application than high mechanical properties or low porosity. In this study, the mechanical stability of the specimens after pyrolysis at 1000 degrees C was investigated. Otherwise, if the thermal treatment is continued, subsequent gas pressure sintering leads to a dense Si3N4-ceramic. The low sinter shrinkage of the precursor-powder-derived ceramic reduces the hard machining effort and offers a better use of the space inside the sinter furnaces. Moreover, Raman spectroscopy showed, that silicon carbide was formed in the specimens. Consequently, further investigations on both the pyrolyzed and the sintered materials are necessary. Especially, investigations on the microstructure and the mechanical strength of the sintered Si3N4/SiC ceramic should clarify, if nano-or micro-scaled SiC segregations are formed during the sinter process and if they improve the fracture toughness of the Si3N4 ceramic.