SiC-platelet orientation in a liquid phase sintered silicon carbide composite formed by thermoplastic forming techniques

Thermoplastic forming techniques were used to study the alignement of the platelets (d50 = 14 mm, 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 alignement of the platelets corresponding to the flow of the mixtures was observed. In some shapes there was a perfect alignement of the platelets preventing the formation of a platelet framework and resulting in high sintering densities of > 97 percent th.D. with 20 percent platelet co ntent. This essentially demonstrates the opportunity of making dense platelet reinforced composites by pressureless sintering.