Shaping of si3n4 ceramics with wet methods

The production of complex shaped ceramic parts in many technological areas can be performed by green machining. This situation causes a high processing cost. Therefore, slurry based methods such as direct coagulation casting (DCC) and additive manufacturing have been developed. With these methods, it can be produced by little or no machining. In this thesis study, the production of high performance complex shaped Si3N4 ceramic parts by using DCC and robocasting methods was aimed. Within this scope, workable slurries with suitable fluidity were prepared by using Vesta powder (P95H 50 vol%) and Ube powder (SN-E10, 42 vol%) for the shaping with DCC method. The density, microstructure and mechanical properties of the ceramic parts shaped by coagulation using 2 vol% glycerol diacetate were investigated. In the DCC process, there is a possibility of air bubble residue in the microstructure, therefore, it is found that cold isostatic pressing is necessary for the product having reliable mechanical properties. In shaping with robocasting method, the yield point of stable colloidal suspension prepared with a 50 vol% solid content and 1 wt% polyethylenimine (Mw: 25 000 gr/mol) were investigated by using flocculating ammonium polyacrylate. It was observed that the slurries having a yield point range of 90-175 Pa can be successfully printed. When the sections of the sintered bodies were examined, it was determined that the adhesion between the layers of the parts was quite good and the density of the products printed by robocasting was found to be over 99%. It was revealed that DCC and robocasting methods can be used for the production of special complex shaped ceramic parts.