Effect of residual porosity and pore structure on the mechanical strength of SiC-Al₂O₃-Y₂O₃

Effect of residual porosity on the flexural strength of sintered α-SiC ceramic with Al₂O₃ and Y₂O₃ as sintering aids was investigated. The flexural strength (σ)-porosity (p) behaviour of the SiC ceramics was experimentally derived based on the minimum solid area approach. Both the data from the present work and those available in the literature can be simply and well-expressed by an exponential function at a correlation coefficient as good as r² ≃ 0.90: σ = 915exp(-9.0p)MPa The value of the exponent constant (9.0) agrees reasonably with that theoretically predicted by using the approach for an extreme of idealized oblate spheroids. The pore structure appeared to have little or no influence on the exponential σ-p behaviour, except for the presence of surface pores which act as fracture flaws leading to a major deterioration of mechanical strength compared to the predicted one.