High toughness in laminated SiC ceramics from aqueous tape casting

Toughness as high as 9.5 MPa · m^1/2 was achieved in a SiC material prepared from aqueous tape casting, laminating and hot pressing. The increased toughness is related to the formation of second phase at triple pockets, YAlO₃, which was different from the composition of sintering additives Al₂O₃ and Y₂O₃ (Y₃Al₅O₁₂). The extra Al₂O ₃ was found at thin amorphous films covering most grain boundaries where Y₂O₃ was absent. A similar difference between the initial additive composition and the final second phase was found in another SiC material with lower toughness. It is proposed that the presence of thermal residual stress at second phase is responsible for the improvement in fracture toughness.