Fracture toughness reinforcement on α‐cristobalite‐precipitated 3/2‐mullite

ABSTRACT In this study, it is attempted to improve the fracture toughness of 3/2‐mullite (3Al 2 O 3 2SiO 2 or Al 6 Si 2 O 13 ) by precipitating α‐cristobalite. All specimens were prepared from raw‐alumina (Al 2 O 3 ) and raw‐silica (SiO 2 ) powders using spark plasma sintering. Excess raw‐silica over the ideal composition of 3/2‐mullite was added to the powders to produce α‐cristobalite precipitated in the 3/2‐mullite matrix. The fracture toughness increased to a maximum of 2.60 MPa m 0.5 with 31 vol% α‐cristobalite. The precipitation reinforcement can be explained by an analogy to the residual stress effect based on the conventional crack‐tip shielding model in particle‐dispersed composite. This finding reinforces the fracture toughness based on the precipitated phase in the composite rather than using conventional additives.