The effect of powder type and CaO additive on properties of sintered SiC by pressureless sintering in additive system of Al2O3-Y2O3-CaO

In this study, the effect of two types of SiC powders consist of SiC-1 (β-SiC) and SiC-2 (β-SiC+α-SiC) and also different values of CaO additive consist of 0, 0.4 and 0.8 weight percent on sintering behavior of sintered SiC with pressureless technique in Al2O3-Y2O3-CaO additive system  was investigated. In all specimens, Al2O3:Y2O3 molar ratio was equal to 3:2 and all amounts of additive were equal to 9 weight percent. Specimens were sintered at 1900ºC for 1 hour in argon atmosphere. Results show that relative density, elastic modulus, micro hardness and fracture toughness of specimens sintered with SiC-2 is higher than specimens sintered with SiC-1. Also results showed that by adding CaO to 0.4 weight percent in both SiC powder types, sinterability increased and by increasing CaO amount to 0.8 weight percent, sinterability decreased. Maximum value of relative density and elastic modulus in specimens sintered with SiC-1 were respectively 80.86 % and 273.99±11 GPa and in specimens sintered with SiC-2 were respectively 92.34 % and 344.55±8.4 GPa. Also maximum amounts of micro hardness and fracture toughness in specimens sintered with SiC-2 powder and 0.4 weight percent of CaO were obtained 19.5± 0.82 GPa and 4.7± 0.5 MPa.   respectively.