PROGRESS IN THE FABRICATION OF SI3N4 TURB INE ROTORS BY PRESSURE SLIPCASTING

The fabrication of silicon nitride components by pressure slip casting has been studied. Simple as well as more complicated shapes such as s pin test discs, with homogeneous microstructure, were produced using t his technique. Prior to casting in a full-scale pressure casting machi ne, fundamental studies of the casting behaviour of the slips were con ducted using filter pressing experiments. Due to the coarse pore struc ture of the polymeric mould material used special attention was given to the slip proper ties in order to avoid slip penetration into the mo uld and to obtain an adequate consolidation. Parameters like the degre e of particle interaction and solid content as well as the pressure sc hedule were investigated. Partially flocculated slips were found to gi ve considerably faster castings and the obtained bodies sintered to ne arly full density without deformations In pressure casting of spin tes t discs with stabilized slips, optimization of the pressure schedule w as required to avoid cracking caused by stress gradients.