SiC Platelet Orientation in a Liquid-phase-sintered Silicon Carbide Composite Formed by Thermoplastic Forming Techniques

Thermoplastic forming techniques were used to study the alignment of the platelets (d50 = 14 μm, aspect ratio 8-10) and the effect on densification of a liquid-phase-sintered silicon carbide composite. Several ceramic parts (test bars, tubes, discs, rings and balls) were manufactured by injection moulding, hot moulding (low-pressure injection moulding) and thermoplastic extrusion methods. Special binders for injection moulding/extrusion and hot moulding were developed. The feedstocks were characterized by torque rheometry in a sigma-blades kneader and by shear-stress-controlled rotation viscosimetry, respectively. The orientation of the platelets in the matrix material was studied by microscopy. An alignment of the platelets corresponding to the flow of the mixtures was observed. In some shapes there was a perfect alignment of the platelets preventing the formation of a platelet framework and resulting in high sintering densities of > 97% of theoretical with 20% platelet content. This essentially demonstrates the opportunity of making dense, platelet-reinforced composites by pressureless sintering. © 1996 Elsevier Science Limited.