PREPARATION AND CHARACTERIZATION OF FUSED SILICA BASED CERAMIC CORES USED IN SUPERALLOY CASTING

Fused silica based ceramic core samples with different compositions were formed by injection molding and sintered at 1550 degrees C for 1 h Compositions were altered by addition of ZrO2 in either calcined form or stabilized form with 3mol % yttria The effects of crystalline phase content, sintering conditions and grain size on flexural strength porosity and liquid metal interactions of ceramic samples have been investigated The experimental work revealed that the optimal composition for ceramic cores is fused silica with 17 wt% stabilized ZrO2 Increase in fracture strength low shrinkage and low thermal expansion coefficient were the reasons for this selection When tested for metal interaction, the selected ceramic showed no sign of a reaction with metal When penetrated into metal ceramic cracked due to differential densification during sintering differental thermal expansion coefficients loss of adherence between the grains and phase transformation of ZrO2 upon cooling